Insolation

1 Introduction
2 Factors Affecting Insolation
3 Global Patterns of Insolation
4 Heating and Cooling of the Atmosphere
5 Heat Budget
6. Temperature – Introduction
7. Factors Affecting Temperature
8.Temperature Distribution
9. Adiabatic Heating and Cooling
10. Temperature Inversion
11. Temperature Anomaly

1 Introduction

• Solar irradiance (SI) is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
• The solar irradiance integrated over time is called solar irradiation, insolation, or solar exposure. However, insolation is often used interchangeably with irradiance in practice.
• The SI unit of irradiance is watt per square metre (W/m2).
• The earth’s surface receives only a part of this radiated energy (2 units out of 1,00,00,00,000 units of energy radiated by the sun).
• The energy received by the earth’s surface in the form of short waves is termed as Incoming Solar Radiation or Insolation.

• • Moreover, water vapour, dust particles, ozone and other gases present in the atmosphere absorb a small amount of solar radiation.
  • The solar radiation received at the top of the atmosphere varies slightly in a year due to the variations in the distance between the earth and the sun.
  • During the earth’s revolution around the sun, the earth is farthest from the sun on 4th July.
  • This position of the earth is called aphelion. On 3rd January, the earth is nearest to the sun. This position is called perihelion.
  • There are two basic laws which govern the nature and flow of radiation such as

(1) Wien’s displacement law: According to this law wavelength of the radiation is inversely proportional to the absolute temperature of the emitting body.

(ii) Stefan-Boltzman law: This law states that flow or influx, of radiation is proportional to the fourth power of the absolute temperature of radiating body.

Electromagnetic Radiation

EM radiation is classified by wavelength into radio, microwave, infrared, visible, ultraviolet, X-rays and gamma rays.

The electromagnetic radiation radiating from the outer surface of the sun, consisting of four spectrums which are as follows:

(i) The first spectrum includes Gama rays, hard x-rays, soft x- rays and ultraviolet rays. Measured in angstrom (1 (Y’ cm) and have short wavelengths.

(ii) The second spectrum consists of visible rays. It is measured in micron and ranges between 0.4 to 0.07 micron.

(iii) The third spectrum of electromagnetic waves covers infrared spectrum. It ranges between 0.7 to 300 microns.

(iv) The fourth spectrum consists of long waves which include microwaves, radar waves and radio waves. These waves are measured in cm and m.

2 Factors influencing Insolation

The amount of insolation received on the earth’s surface is not uniform everywhere. It varies according to the place and time. When the tropical regions receive maximum annual insolation, it gradually decreases towards the poles. Insolation is more in summers and less in winters. The major factors which influence the amount of insolation received are:

• The Angle of Incidence or the Inclination of the Sun’s Rays
• Duration of Sunshine
• Transparency of Atmosphere
• Land-Sea Differential
• Prevailing Winds
• Aspects of Slope
• Ocean Currents
• Altitude
• Earth’s Distance from Sun
• Sun’s Spot

The Angle of Sun’s Rays.

• Changes in the location of the Sun have a direct effect on the intensity of solar radiation.
• The intensity of solar radiation is largely a function of the angle of incidence, the angle at which the Sun’s rays strike the Earth’s surface.
• If the Sun is positioned directly overhead or 90° from the horizon, the incoming insolation strikes the surface of the Earth at right angles and is most intense.
• If the Sun is 45° above the horizon, the incoming insolation strikes the Earth’s surface at an angle. This causes the rays to be spread out over a larger surface area reducing the intensity of the radiation.

Figure models the effect of changing the angle of incidence from 90 to 45°. As illustrated, the lower Sun angle (45°) causes the radiation to be received over a much larger surface area. This surface area is approximately 40% greater than the area covered by an angle of 90°. The lower angle also reduces the intensity of the incoming rays by 30%.

Source: PhysicalGeography.net | FUNDAMENTALS eBOOK

We can also model the effect the angle of incidence has on insolation intensity with the following simple equation:

Intensity = SIN (A)

where, A is the angle of incidence and SIN is the sine function found on most calculators. Using this equation we can determine that an angle of 90° gives us a value of 1.00 or 100% (1.00 x 100). Let us compare this maximum value with values determined for other angles of incidence. Note the answers are expressed as a percentage of the potential maximum value.

SIN 80 = 0.98 or 98%
SIN 70 = 0.94 or 94%
SIN 60 = 0.87 or 87%
SIN 50 = 0.77 or 77%
SIN 40 = 0.64 or 64%
SIN 30 = 0.50 or 50%
SIN 20 = 0.34 or 34%
SIN 10 = 0.17 or 17%
SIN 0   = 0.00 or 00%

2. Sunshine Hours

• The yearly changes in the position of the Earth’s axis relative to the plane of the ecliptic also causes seasonal variations in day length to all locations outside of the equator.
• Longest days occur during the June solstice for locations north of the equator and on the December solstice for locations in the Southern Hemisphere.
• The equator experiences equal day and night on every day of the year. Day and night is also of equal length for all Earth locations on the September and March equinoxes.
• Figure suggests that days are longer than nights in the Northern Hemisphere from the March equinox to the September equinox.
• Between the September to March equinox days are shorter than nights in the Northern Hemisphere. The opposite is true in the Southern Hemisphere.
• The graph also shows that the seasonal (winter to summer) variation in day length increases with increasing latitude.

3. Transparency of Atmosphere

• The transparency of the atmosphere depends upon the cloud cover and its thickness, dust particles, water vapour, etc. They reflect, absorb or transmit insolation.
• Very small suspended particles in the troposphere scatter visible spectrum both to space and towards the earth’s surface. This process adds colour to the sky.
• The red colour of the rising and the setting sun and the blue colour of the sky are the results of scattering of the light within the atmosphere.

4. Land-Sea Differential

• Albedo of land is much greater than albedo of oceans and water bodies. Especially snow covered areas reflect up to 70%-90% of insolation.
• Average penetration of sunlight is more in water – up to 20 metres, than in land – where it is up to 1 metre only. Therefore, land cools or becomes hot more rapidly compared to oceans. In oceans, continuous convection cycle helps in heat exchange between layers keeping diurnal and annual temperature ranges low. (more while studying salinity and temperature distribution of oceans)
• The specific heat of water is 2.5 times higher than landmass, therefore water takes longer to get heated up and to cool down.

The annual range of temperature in the interior of the continents is high as compared to coastal areas. What is / are the reason / reasons?
1.Thermal difference between land and water
2.Variation in altitude between continents and oceans
3 .Presence of strong winds in the interior
4 Heavy rains in the interior as compared to coasts
Select the correct answer using the codes given below.
(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2, 3 and 4
Solution (a)

5. Aspects of Slope

• The direction of the slope and its angle control the amount of solar radiation received locally. Slopes more exposed to the sun receive more solar radiation than those away from the sun’s direct rays.
• Slopes that receive direct Sun’s rays are dry due to loss of moisture through excess evaporation. These slopes remain barren if irrigational facilities are absent. But slopes with good irrigational facilities are good for agriculture due to abundant sunlight available. They are occupied by dense human settlements.
• Slopes that are devoid of direct sunlight are usually well forested.

6. Altitude

• With increase in height, pressure falls, the effect of greenhouse gases decreases and hence temperature decreases (applicable only to troposphere).
• The normal lapse rate is roughly 1⁰ C for every 165 metres of ascent.

7. Distance between the earth and the sun:

The distance between the earth and the sun is not uniform throughout the year. It is nearest to the sun (147 million km) on 3t January and farthest (152 million km) on 4th July. It is mainly to the orbit of the earth which is elliptical in shape. When the earth is nearest to the sun it is called as perihelion and when farthest is called as aphelion.

8. Sunspots:

Sunspots created on the outer surface due to periodic disturbance and explosions. The number of sunspots varies from year to year. Its cycle is completed in every 1 1 years. The energy radiated from the sun increases. When the number of sunspots increases and therefore the amount of insolation received by the earth surface is also increases.

3. Global Patterns of Insolation

Patterns of insolation and net radiation which determine the location of plants, animals, climate, soils and other elements of our physical environment. From approximately 350N to 350S latitude there is a surplus of energy as incoming radiation exceeds outgoing. Pole wards from 350N & S latitude there is more outgoing energy than incoming, yielding a net loss of energy from the Earth’s surface. One might ask then why the middle to higher latitudes aren’t getting colder through time as a result of the net loss, and the subtropical to

equatorial regions getting constantly hotter due to the net gain. The reason is that the energy is redistributed by circulation of the atmosphere and oceans. Heat gained in the tropics is transported pole ward by the global circulation of air and warm ocean currents to heat higher latitude regions. Cooler air from the higher latitudes and cold ocean currents push equator ward to cool the lower latitudes. This process of redistributing energy in the Earth system helps maintain a long-term energy balance.

Insolation

the geographic distribution of insolation. For the Earth as a whole, particular patterns can be accounted for by variation in surface features that impact insolation. Insolation maxima are found in the tropical and subtropical deserts of the earth. Here, high sun angles and a lack of cloud cover in desert regions allow much solar radiation to the surface. Insolation decreases to a minimum at the poles where low sun angles and the fact that the Sun doesn’t rise above the horizon nearly half the year reduces annual insolation.

The three major heat zones based on the distance from the equal on the earth are temperate zone, the Torrid Zone and the Frigid Zone.

Torrid Zone (Tropical Zone)

This is the hottest zone of the earth. The region that lies from the Tropic of Cancer (23.5 °N), across equator (00) to the Tropic of Capricorn (23.5 °S) is considered as the Torrid Zone (Tropical Zone). The sun’s rays directly fall at least once a year in this region.

Frigid Zone

This is the coldest zone on the earth. This region lies to the north of Arctic circle (66.6 °N) and to the south of the Antarctic circle (66.5 °S) and is permanently frozen. There is no sunlight for most of the months in a year in this zone.

Temperate Zone

This is the habitable heat zone on the earth. There are two temperate zones lie in between 23 1/2° and 66 1/2° in both the hemisphere. These regions have moderate, tolerable temperature.

Over the course of a year, the most obvious pattern is seasonal changes in net radiation. Incoming sunlight increases in the hemisphere experiencing summer, which makes the energy imbalance strongly positive (more watts of energy coming in than going out). As the September equinox approaches, a zone of positive net radiation is nearly centered over the equator, and energy deficits lie over the poles. As the season changes into winter, the net radiation becomes negative across much of the Northern Hemisphere and positive in the Southern Hemisphere. The pattern reverses on the March equinox.

Over the course of a year, the most obvious pattern is seasonal changes in net radiation. Incoming sunlight increases in the hemisphere experiencing summer, which makes the energy imbalance strongly positive (more watts of energy coming in than going out). As the September equinox approaches, a zone of positive net radiation is nearly centered over the equator, and energy deficits lie over the poles. As the season changes into winter, the net radiation becomes negative across much of the Northern Hemisphere and positive in the Southern Hemisphere. The pattern reverses on the March equinox.

Averaged over the year, there is a net energy surplus at the equator and a net energy deficit at the poles. This equator-versus-pole energy imbalance is the fundamental driver of atmospheric and oceanic circulation.

The earth-atmosphere energy balance is achieved as the energy received from the Sun balances the energy lost by the Earth back into space. In this way, the Earth maintains a stable average temperature and therefore a stable climate. Using 100 units of energy from the sun as a baseline the energy balance.

4. Heating and Cooling of the Atmosphere

The heat energy from the solar radiation is received by the earth through three mechanisms Radiation

Heat transfer from one body to another without actual contact or movement. It is possible in relatively emptier space, for instance, from the sun to the earth through space. Conduction

Heat transfer through matter by molecular activity. Heat transfer in iron and other metals is by conduction. Generally, denser materials like water are good conductors and a lighter medium like air is a bad conductor of heat. Convection

Transfer of heat energy by actual transfer of matter or substance from one place to another. (heat transfer by convection cycles in atmosphere as well as oceans)

5. Heat Balance of the Earth

Albedo

The term albedo refers to the amount of solar energy that gets reflected off of the Earth and lands back in space. It is a reflection coefficient and has a value less than one. When the solar radiation passes through the atmosphere, some amount of it is reflected, scattered and absorbed. The reflected amount of radiation is called as the albedo of the earth.

Terrestrial albedo – Any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body. When seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4. The average albedo of Earth is about 0.3.  This is far higher than for the ocean primarily because of the contribution of clouds.

Sample albedos

Astronomical albedo – The albedos of planets, satellites and minor planets such as asteroids can be used to infer much about their properties. The study of albedos, their dependence on wavelength, lighting angle (“phase angle”), and variation in time composes a major part of the astronomical field of photometry. 

72.Consider the following statements:[2008]
l.Albedo of an object determines its visual brightness when viewed with reflected light. 2.Albedo of Mercury is much greater than the albedo of the Earth. Which of the statements given above is/are correct? (a)1 only (b)2 only (c)Both 1 and 2 (d)Neither 1 nor 2
Ans. 72.(a)Albedo is the fraction of the incident sunlight that is reflected. When an object reflects most of the light that hits it and looks bright then it has high albedo. Albedo of mercury is 0.1 and that of the earth is 0.30.
80.Which one of the following reflects back more sunlight as compared to other three?[2010] (a)Sand desert (b)Paddy crop (c)Land covered with fresh snow (d)Prairie land
Ans. d

6. Temperature – An Introduction

Theoretically, the coldest a system can be is when its temperature is absolute zero, at which point the thermal motion in matter would be zero. However, an actual physical system or object can never attain a temperature of absolute zero. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, and −459.67 °F on the Fahrenheit scale.

The dry-bulb temperature (DBT) is the temperature of air measured by a thermometer freely exposed to the air, but shielded from radiation and moisture.

The wet-bulb temperature (WBT) is the temperature read by a thermometer covered in water-soaked cloth (wet-bulb thermometer) over which air is passed. At 100% relative humidity, the wet-bulb temperature is equal to the air temperature (dry-bulb temperature) and it is lower at lower humidity.

7. Factors Affecting Temperature

The factors responsible for the uneven horizontal distribution of temperature are:

A. LATITUDE

In the previous article, we have studied that the angle of incidence of sun’s rays goes on decreasing from the equator towards the poles.

Higher the angle of incidence, higher is the temperature. Similarly, lower the angle of incidence, lower is the temperature.

This is why the temperature is higher near the tropical regions and decreases towards the poles.

B. ALTITUDE

As we all know, the temperature in the troposphere goes on decreasing with increase in height.

Temperature decreases at an average rate of nearly 6 degree Celsius per 1000 m altitude, which is known as Normal Lapse Rate.

C. LAND AND SEA CONTRAST

Compared to land, the sea gets heated slowly and loses heat slowly. Land heats up and cools down quickly.

As a result, the temperature is relatively higher on land during day time and it is higher in water during the night.

Also, the places situated near the sea come under the moderating influence of the sea and land breezes which moderates the temperature.

There are also seasonal variations in the temperature of land and sea. During summer, the air above land has a higher temperature than the oceans. But the air above oceans gets higher temperature than landmass in winter.

Notwithstanding the great contrast between land and water surfaces, there are differences in the rate of heating of different land surfaces. A snow-covered land as in polar areas warms very slowly because of a large amount of reflection of solar energy. A vegetation covered land does not get excessively heated because a great amount of insolation is used in evaporating water from the plants.

100.The annual range of temperature in the interior of the continents is high as compared to coastal areas.
What is/are the reason/reasons?[2013 – I]
1.Thermal difference between land and water 2.Variation in altitude between continents and oceans 3.Presence of strong winds in the interior 4.Heavy rains in the interior as compared to coasts Select the correct answer using the codes given below. (a)1 only
(b)1 and 2 only (c)2 and 3 only (d)1, 2, 3 and 4
Ans. 100.(a)The first statement is correct. One major factor affecting the distribution of the temperature of Earth is distribution of Land and Oceans. Since there is more land in Northern Hemisphere and more waters in Southern hemisphere and there is a big difference between the specific heat of land and water; the loss of heat from the continents is bigger than the oceans. The continents get heated faster and get cooled faster in comparison to the Oceans. This is the reason that the temperatures of the Oceans are moderate while that of continents is extreme. The moderating effect on temperature of the land due to proximity of the seas is called Maritime influence. The increasing effect on temperature of the land at interior of the continents is called Continental Influence.

D. OCEAN CURRENTS

Ocean Currents are of two types – warm and cold.

Warm currents make the coasts along which they flow warmer, while cold currents reduce the temperature of the coasts along which they flow.

The North-Western European Coasts do not freeze in winter due to the effect of North Atlantic Drift (a warm current), while the Quebec on the coast of Canada is frozen due to the Cold Labrador Current flowing along it, though the Quebec is situated in lower latitudes than the North-West European Coast.

E. AIR MASSES

Like the land and sea breezes, the passage of air masses also affects the temperature.

The places, which come under the influence of warm air masses experience higher temperature and the places that come under the influence of cold air masses experience low temperature.

F. VEGETATION COVER

Soil devoid of vegetation cover receives heat more rapidly than the soil under vegetation cover. Because vegetation cover absorbs much of sun’s heat and then prevents quick radiation from the earth whereas the former radiates it more rapidly.

Hence the temperature variations in densely forested areas are lower than those in desert areas.

7. Distribution of Temperature

A. Horizontal Distribution of Temperature:

The horizontal or latitudinal distribution of temperature is shown with the help of a map with isotherms (i.e., imaginary lines joining places having equal temperatures, reduced to sea level to eliminate the effects of altitude.) Isotherms have three general characteristics:

1. Isotherms tend east-west, generally following the parallels.

2. Isotherms take sudden bends where land- water contrasts are maximum.

3. The spacing of isotherms indicates the latitudinal thermal gradient i.e. steepness or slow gradual nature of temperature change. Thus, close spacing indicates a rapid change in the temperature and wide spacing means slow change.

General Isothermal Trend:

• Generally follow the parallels: Isotherms have close correspondence with the latitude parallels mainly because the same amount of insolation is received by all the points located on the same latitude.
• Sudden bends at ocean – continent boundaries: Due to differential heating of land and water, temperatures above the oceans and landmasses vary even on the same latitude. (we have seen how land sea differential effects temperature distribution)
• Narrow spacing between isotherms indicate rapid change in temperature (high thermal gradient).
• Wide spacing between isotherms indicate small or slow change in temperatures (low thermal gradient).

General Temperature Distribution

• The highest temperatures occur over tropics and sub-tropics (high insolation). The lowest temperatures occur in polar and sub polar regions. in continents due to the effect of continentiality.
• Diurnal and annual range of temperatures are highest in the interiors of continents due to the effect of continentiality (in continental interiors these will no moderating effect of oceans).
• Diurnal and annual range of temperatures are least in oceans. [high specific heat of water and mixing of water keep the range low]
• Low temperature gradients are observed over tropics (sun is almost overhead the entire year) and high temperature gradients over middle and higher latitudes (sun’s apparent path varies significantly from season to season).
• Temperature gradients are usually low over the eastern margins of continents. (This is because of warm ocean currents)
• Temperature gradients are usually high over the western margins of continents. (This is because of cold ocean currents)
• The isotherms are irregular over the northern hemisphere due to an enhanced land-sea contrast. Because of predominance of land over water in the north, the northern hemisphere is warmer. The thermal equator (ITCZ) lies generally to the north of geographical equator.
• The isotherms are irregular over the northern hemisphere due to an enhanced land-sea contrast. Because of predominance of land over water in the north, the northern hemisphere is warmer. The thermal equator (ITCZ) lies generally to the north of geographical equator.
• While passing through an area with warm ocean currents, the isotherms show a poleward shift. (North Atlantic Drift and Gulf Stream combined with westerlies in Northern Atlantic; Kurishino Current and North Pacific current combined with westerlies in Northern Pacific) (we will see about ocean currents in detail later.)
• Mountains also affect the horizontal distribution of temperature. For instance, the Rockies and the Andes stop the oceanic influence from going inwards into North and South America.

Seasonal Temperature Distribution

• The global distribution of temperature can well be understood by studying the temperature distribution in January and July.
• The temperature distribution is generally shown on the map with the help of isotherms. The Isotherms are lines joining places having equal temperature.
• In general the effect of the latitude on temperature is well pronounced on the map, as the isotherms are generally parallel to the latitude. The deviation from this general trend is more pronounced in January than in July, especially in the northern hemisphere.
• In the northern hemisphere the land surface area is much larger than in the southern hemisphere. Hence, the effects of land mass and the ocean currents are well pronounced.

Seasonal Temperature Distribution – January

• During January, it is winter in the northern hemisphere and summer in the southern hemisphere.
• The western margins of continents are warmer than their eastern counterparts, since the Westerlies are able to carry high temperature into the landmasses.
• The temperature gradient is close to the eastern margins of continents. The isotherms exhibit a more regular behavior in the southern hemisphere.

Northern Hemisphere

• The isotherms deviate to the north over the ocean and to the south over the continent. This can be seen on the North Atlantic Ocean.
• The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms show a poleward shift indicating that the oceans are warmer and are able to carry high temperatures poleward.
• An equator ward bend of the isotherms over the northern continents shows that the landmasses are overcooled and that polar cold winds are able to penetrate southwards, even in the interiors. It is much pronounced in the Siberian plain.
• Lowest temperatures are recorded over northern Siberia and Greenland.

Southern Hemisphere

• The effect of the ocean is well pronounced in the southern hemisphere. Here the isotherms are more or less parallel to the latitudes and the variation in temperature is more gradual than in the northern hemisphere.
• The high temperature belt runs in the southern hemisphere, somewhere along 30°S latitude.
• The thermal equator lies to the south of geographical equator (because the Intertropical Convergence Zone or ITCZ has shifted southwards with the apparent southward movement of the sun).

Seasonal Temperature Distribution – July

• During July, it is summer in the northern hemisphere and winter in the southern hemisphere. The isothermal behavior is the opposite of what it is in January.
• In July the isotherms generally run parallel to the latitudes. The equatorial oceans record warmer temperature, more than 27°C. Over the land more than 30°C is noticed in the subtropical continental region of Asia, along the 30° N latitude.

Northern Hemisphere

• The highest range of temperature is more than 60° C over the north-eastern part of Eurasian continent. This is due to continentality. The least range of temperature, 3°C, is found between 20° S and 15° N.
• Over the northern continents, a poleward bend of the isotherms indicates that the landmasses are overheated and the hot tropical winds are able to go far into the northern interiors.
• The isotherms over the northern oceans show an equator ward shift indicating that the oceans are cooler and are able to carry the moderating effect into tropical interiors. The lowest temperatures are experienced over Greenland.
• The highest temperature belt runs through northern Africa, west Asia, north-west India arid southeastern USA. The temperature gradient is irregular and follows a zig-zag path over the northern hemisphere.

Southern Hemisphere

• The gradient becomes regular over the southern hemisphere but shows a slight bend towards the equator at the edges of continents. Thermal equator now lies to the north of the geographical equator.

B. Vertical Distribution of Temperature:

The normal, lapse rate is uniform at a given level at all latitudes within the troposphere. At the tropopause, the lapse rate stops at zero i.e. there is no change in temperature there. In the lower stratosphere, the lapse rate remains constant for some height, while higher temperatures exist over the poles because this layer is closer to earth at the poles.

9. Adiabatic Heating and Cooling:

Adiabatic cooling is the process of reducing heat through a change in air pressure caused by volume expansion. In data centers and other facilities,adiabatic processes have enabled free cooling methods, which use freely available natural phenomena to regulate temperature.

10. Temperature Inversion:

Temperature inversion, a reversal of the normal behaviour of temperature in the troposphere (the region of the atmosphere nearest the Earth’s surface), in which a layer of cool air at the surface is overlain by a layer of warmer air. (Under normal conditions air temperature usually decreases with height.)

The sloping surface underneath makes them move towards the bottom where the cold layer settles down as a zone of low temperature while the upper layers are relatively warmer. This condition, opposite to normal vertical distribution of temperature, is known as Temperature Inversion. This phenomenon is specially observed in the intermontane valleys. In other words, the vertical temperature gets inverted during temperature inversion.

92.Normally, the temperature decreases with the increase in height from the Earth’s surface, because[2012 – I] 1.the atmosphere can be heated upwards only from the Earth’s surface 2.there is more moisture in the upper atmosphere 3.the air is less dense in the upper atmosphere Select the correct answer using the codes given below: (a)1 only (b)2 and 3 only (c)1 and 3 only (d)1, 2 and 3
Ans. 92.(c)Atmosphere is heated by infrared radiation, Moisture is more in lower atmosphere. In the upper atmosphere Air is less dense which hold less heat thus temperature is low.

Ideal Conditions for Temperature Inversion:

Temperature inversion takes place only under certain specific conditions.

These conditions are:

1. Long nights, so that the outgoing radiation is greater than the incoming radiation.

2. Clear skies, which allow unobstructed escape of radiation.

3. Calm and stable air, so that there is no vertical mixing at lower levels.

Types of Temperature Inversion:

Depending on the nature of underlying surface and reasons for the temperature contrast, there are four types of temperature inversion:

1. Air Drainage Type of Inversion:

This type of inversion occurs in a valley, where the dense, cold lower level air slides or drains down a slope to settle down at the bottom of the valley. As a result the valley floor has a lower temperature gradient than the upper layers, which are relatively warm.

2. Surface Temperature Inversion:

This is the most common type of temperature inversion and occurs even on relatively plain surfaces. A rapid radiation of heat occurs in places where the air is still, clear and

dry and the winter nights are long. The temperature, as a consequence, falls rapidly and temperature inversion takes place. This temperature inversion is not very deep and is destroyed as the sun rises.

3. Advectional type of Temperature Inversion:

There are places where many types of airmasses meet. The colder airmass, being heavy, settles down, while the warmer airmass, being light, rises over the colder airmass. This creates temperature inversion. This types of inversion is unstable and is destroyed as the weather changes.

4. Upper Surface Temperature Inversion:

Sometimes massive upper layers descend and press the layers below them. As a result the upper layers get warmed up and settle over the cold layers, and temperature inversion takes place. This keeps the atmosphere stable for a long time. Such a condition exists in dry atmosphere. In the winters of mid-latitudinal continental areas, stable high pressure conditions are created, as mentioned above, and create temperature inversion. This temperature inversion is called upper surface temperature inversion because it takes place in the upper parts of the atmosphere.

11. Temperature Anomaly

The difference between the mean temperature of a place and the mean temperature of its parallel (latitude) is called the temperature anomaly or thermal anomaly. It expresses deviation from the normal. The temperature variation along a latitude varies on account of altitude, land-water contrasts, prevailing winds and ocean currents.

The largest anomalies occur in the northern hemisphere and the smallest in the southern hemisphere. The anomaly is said to be negative when the temperature at a place is less than the expected temperature of the latitude. Conversely, the anomaly is positive when the temperature at a place is more than the expected temperature of the latitude. For the year as a whole, the anomalies are negative over the continents from about 40° latitude towards the poles and positive towards the equator. Over the oceans, the anomalies are positive pole-ward from about 40° latitude and negative towards the equator.

97.Consider the following pairs:[2013 – I]
1.Electromagnetic radiation 2.Geothermal energy 3.Gravitational force 4.Plate movements 5.Rotation of the earth 6.Revolution of the earth
Which of the above are responsible for bringing dynamic changes on the surface of the earth?
(a)1, 2, 3 and 4 only (b)1, 3, 5 and 6 only (c)2, 4, 5 and 6 only (d)1, 2, 3, 4, 5 and 6
Ans. 97.(d)From electromagnetic radiation to revolution of the earth, everything is responsible for bringing dynamic changes on the surface of the earth. For example: Electromagnetic radiation brings changes in the field of microwaves, wavelengths of radio, UV rays, infra red rays, X rays and gamma rays. Geothermal energy is the heat received from the earth’s core. This heat continuously flows outward. It transfers to the surrounding layers of rock, the mantle. When temperature and pressure becomes very high some mantle rocks melt becoming magma. It then either comes out as lava or heat up the nearby rocks and water which comes out as hot springs or geysers. Gravitational force is constantly working on all physical bodies. It is giving weights to objects with mass and causes them to fall to the ground when dropped. Plate movement is a dynamic change on the surface of the earth. It explains many aspects of the interrelationship of volcanoes, earthquakes, climate change, and the evolution of life itself. Everything about our planet is related either directly or indirectly to plate tectonic. Rotation causes day and night. Revolution causes seasons, change in the length of day and night.

.

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Pressure and Winds

PART – A – Atmospheric Pressure

1 Pressure Systems
2 Factors Influencing Atmospheric Pressure
3 Pressure Regions/Belts
4 Shifting Pressure Belts
5 Pressure Belts in July and in January

1 Pressure Systems

• The atmosphere is made up of gases that have mass, and so the atmosphere has weight because this mass is pulled toward Earth by gravity. Atmospheric pressure is the force exerted by the weight of these gas molecules on a unit of area of Earth’s surface or on any other body.
• At sea level, the pressure (the “weight”) exerted by the atmosphere is about 14.7 pounds per square inch, or in S.I. units, or 1013.529 millibar, or about 10 newtons (N) per square centimeter.
• The surface pressure at sea level varies minimally, with the lowest value measured 870 millibar and the highest recorded 1085.7 millibar.
• Atmospheric pressure is measured by means of an instrument called barometer.
• The units used by meteorologists for this purpose are called millibars (mb).
• One millibar is equal to the force of one gram on a square centimeter. A pressure of 1000 millibars is equal to the weight of 1.053 kilograms per square centimeter.
• The distribution of atmospheric pressure is shown on a map by isobars, An isobar is an imaginary line drawn through points of
• equal atmospheric pressure at the sea level. The spacing of isobars expresses the rate and direction of pressure change and is called pressure gradients.

2 Factors Influencing Atmospheric Pressure

Atmospheric pressure is affected by differences in

• Air density
• Air temperature, and
• Air movement.

The pressure, temperature, and density of a gas are all related to each other—if one of those variables changes, it can cause changes in the other two.

The Ideal Gas Law: The relationship between pressure, temperature, and density can be summarized by an equation called the ideal gas law:

P= pRT

where P is pressure, p(“rho”) is density, R is the constant of proportionality, and T is temperature. Explained with words, this equation says that pressure (P) will increase if density remains constant but temperature (T) increases, and that pressure will increase if temperature remains constant but density (p) increases.

Density and Pressure Relationships

The pressure exerted by a gas is proportional to its density. The denser the gas, the greater the pressure.

Temperature and Pressure Relationships

The air pressure will be high on warm days and low on cold days. Such is not usually the case, however; warm air is generally associated with low atmospheric pressure and cool air with high atmospheric pressure.

Air Movement and Pressure Relationships

Some useful generalizations about the factors associated with areas of high pressure and low pressure near the surface can be made:

Strongly descending air is usually associated with high pressure at the surface—a dynamic high.

Very cold surface conditions are often associated with high pressure at the surface—a thermal high.

Strongly rising air is usually associated with low pressure at the surface—a dynamic low.

Very warm surface conditions are often associated with relatively low pressure at the surface—a thermal low.

Vertical Variation of Pressure

• In general, the atmospheric pressure decreases on an average at the rate of about 34 millibars every 300 metres of height.
• The vertical pressure gradient force is much larger than that of the horizontal pressure gradient. But, it is generally balanced by a nearly equal but opposite gravitational force. Hence, we do not experience strong upward winds.
• Due to gravity the air at the surface is denser and hence has higher pressure. Since air pressure is proportional to density as well as temperature, it follows that a change in either temperature or density will cause a corresponding change in the pressure.
• The pressure decreases with height. At any elevation it varies from place to place and its variation is the primary cause of air motion, i.e. wind which moves from high pressure areas to low pressure areas.
• A rising pressure indicates fine, settled weather, while a falling pressure indicates unstable and cloudy weather.

Level                     Pressure               Temp °C

• Sea Level      1,013.25 mb             15.2
• 1 km              898.76 mb                  8.7
• 5km               540.48 mb               -17. 3
• 10km             265.00 mb             -49.7

Horizontal Distribution of Pressure

• Pressure difference generate wind direction and velocity.
• Isobars are lines connecting places having equal pressure.
• Close spacing of isobars indicates a steep or strong pressure gradient, while wide spacing suggests weak gradient.
• The pressure gradient may thus be defined as the decrease in pressure per unit distance in the direction in which the pressure decreases most rapidly.
• There are distinctly identifiable zones of homogeneous horizontal pressure regimes or ‘pressure belts’. On the earth’s surface, there are in all seven pressure belts.

The seven pressure belts are :

• Equatorial low,
• The subtropical highs,
• The sub-polar lows, and
• The polar highs.

(i) Equatorial Low Pressure Belts

• This low pressure belt extends from 0 to 5° North and South of Equator. Due to the vertical rays of the sun here, there is intense heating.
• The air therefore, expands and rises as convection current causing a low pressure to develop here.
• This low pressure belt is also called as doldrums, because it is a zone of total calm without any breeze.
• This belt is also known as Doldrums.

(ii) Subtropical High Pressure Belts

• At about 30°North and South of Equator lies the area where the ascending equatorial air currents descend. This area is thus an area of high pressure. It is also called as the Horse latitude.
• Winds always blow from high pressure to low pressure. So the winds from subtropical region blow towards Equator as Trade winds and another wind blows towards Sub-Polar Low-Pressure as Westerlies.

70.Consider the following statements:[2007] 1.Either of the two belts over the oceans at about 30° to 35° N and S Latitudes is known as Horse latitude. 2.Horse latitudes are low pressure belts. Which of the statements given above is/are correct? (a)1 only (b)2 only (c)Both 1 and 2 (d)Neither 1 nor 2
Ans. 70.(a)The horse latitudes are located between latitude 30°–35° north and south of the equator. The region lies in an area where there is a ridge of high pressure that circles the earth. The ridge of high pressure is also called a sub-tropical high.

(iii) Circum-Polar Low Pressure Belts

• These belts located between 60° and 70° in each hemisphere are known as Circum-Polar Low Pressure Belts.
• In the Subtropical region the descending air gets divided into two parts. One part blows towards the Equatorial Low Pressure Belt. The other part blows towards the Circum- Polar Low Pressure Belt.
• This zone is marked by ascent of warm Subtropical air over cold polar air blowing from poles. Due to earth’s rotation, the winds surrounding the Polar region blow towards the Equator.
• Centrifugal forces operating in this region create the low pressure belt appropriately called Circumpolar Low Pressure Belt. This region is marked by violent storms in winter.

Assertion (A) : 60° – 65º latitudes in both the hemispheres have a low pressure belt instead of high pressure. Reason (R) : The low pressure areas are permanent over oceans rather than on land.[2002] (a)Both A and R are true and R is the correct explanation of A (b)Both A and R are true but R is NOT a correct explanation of A (c)A is true but R is false (d)A is false but R is true
Ans. (c)A is true but R is false. Sub-polar low pressure is located between 60–65º latitude in both hemisphere. Low pressure is produced in this area, because the surface air spreads outward from this zone due to rotation of earth.

(iv) Polar High Pressure Areas

• At the North and South Poles, between 70° to 90° North and South, the temperatures are always extremely low.
• The cold descending air gives rise to high pressures over the Poles. These areas of Polar high pressure are known as the Polar Highs.
• These regions are characterised by permanent Ice Caps.

SHIFTING OF PRESSURE BELTS

Shifting is because the earth is inclined 23 1/2° towards the sun. January represents winter season and July, summer season in the Northern Hemisphere. Opposite conditions prevail in the Southern Hemisphere.

21 June & 22 December

When the sun is overhead on the Tropic of Cancer (21 June) the pressure belts shift 5° northward and when it shines vertically overhead on Tropic of Capricorn (22 December), they shift 5° southward from their original position.

The shifting of the pressure belts cause seasonal changes in the climate, especially between latitudes 30° and 40° in both hemispheres. In this region the Mediterranean type of climate is experienced because of shifting of permanent belts southwards and northwards with the overhead position of the sun. During winters Westerlies prevail and cause rain. During summers dry Trade Winds blow offshore and are unable to give rainfall in these regions. When the sun shines vertically over the Equator on 21st March and 23rd September (the Equinoxes), the pressure belts remain balanced in both the hemispheres.

Pressure Belts in July and in January

Pressure belts in July

In the northern hemisphere, during summer, with the apparent northward shift of the sun, the thermal equator (belt of highest temperature) is located north of the geographical equator. The pressure belts shift slightly north of their annual average locations.

Pressure belts in January

During winter, these conditions are completely reversed and the pressure belts shift south of their annual mean locations. Opposite conditions prevail in the southern hemisphere. The amount of shift is, however, less in the southern hemisphere due to predominance of water.

Similarly, distribution of continents and oceans have a marked influence over the distribution of pressure. In winter, the continents are cooler than the oceans and tend to develop high pressure centres, whereas in summer, they are relatively warmer and develop low pressure. It is just the reverse with the oceans.

PART B.

1. Winds – An Introduction

2. Forces influencing winds

3. General circulation of the atmosphere

4. Classification of Winds

Winds – An Introduction

Wind can be defined simply as air in motion. This motion can be in any direction, but in most cases the horizontal component of wind flow greatly exceeds the flow that occurs vertically. The speed of wind varies from absolute calm to speeds as high as 380 kilometers per hour.

Wind develops as a result of spatial differences in atmospheric pressure. Generally, these differences occur because of uneven absorption of solar radiation at the Earth’s surface . Wind speed tends to be at its greatest during the daytime when the greatest spatial extremes in atmospheric temperature and pressure exist.

Wind is often described by two characteristics: wind direction and wind speed

Wind speed is the velocity attained by a mass of air traveling horizontally through the atmosphere. Wind speed is often measured with an anemometer in kilometers per hour (kmph), miles per hour (mph), knots, or meters per second (mps).

Wind direction is measured as the direction from where a wind comes from. For example, a southerly wind comes from the south and blows to the north. Direction is measured by an instrument called a wind vane. Both of these instruments are positioned in the atmospheric environment at a standard distance of 10 meters above the ground surface.

Wind speed can also be measured without the aid of instruments using the Beaufort wind scale . This descriptive scale was originally developed by Admiral Beaufort of the British Navy in the first decade of the 17th century. The Beaufort system has undergone several modifications to standardize its measurement scale and to allow for its use on land. Users of this scale look for specific effects of the wind on the environment to determine speed

2. Force that can act on moving air.

Following are the four forces act on moving air

• Pressure gradient force

• Coriolis force

• Centripetal acceleration

• frictional deceleration

Pressure gradient force

Pressure gradient force is the primary force influencing the formation of wind from local to global scales. This force is determined by the spatial pattern of atmospheric pressure at any given moment in time. Figure illustrates two different pressure gradient scenarios and their relative effect on wind speed.

Pressure gradient force is the primary force influencing the formation of wind from local to global scales. This force is determined by the spatial pattern of atmospheric pressure at any given moment in time. Figure illustrates two different pressure gradient scenarios and their relative effect on wind speed.

Coriolis force

The rotation of the Earth creates another force, termed Coriolis force, which acts upon wind and other objects in motion in very predictable ways. In the Northern Hemisphere, wind is deflected to the right of its path, while in the Southern Hemisphere it is deflected to the left. The magnitude of the Coriolis force varies with the velocity and the latitude of the object . Coriolis force is absent at the equator, and its strength increases as one approaches either pole. Furthermore, an increase in wind speed also results in a stronger Coriolis force, and thus in greater deflection of the wind. Coriolis force only acts on air when it has been sent into motion by pressure gradient force. Finally, Coriolis force only influences wind direction and never wind speed. The strength of Coriolis force is influenced by latitude and the speed of the moving object.

82.What causes wind to deflect toward left in the Southern Hemisphere?[2010] (a)Temperature (b)Magnetic field (c)Rotation of the earth (d)Pressure
Ans. 82.(c)Rotation of the earth causes wind to deflect towards left in the Southern Hemisphere.

Centripetal acceleration

Centripetal acceleration is the third force that can act on moving air. It acts only on air that is flowing around centers of circulation. Centripetal acceleration is also another force that can influence the direction of wind. Centripetal acceleration creates a force directed at right angles to the flow of the wind and inwards towards the centers of rotation (e.g., low and high pressure centers). This force produces a circular pattern of flow around centers of high and low pressure. Centripetal acceleration is much more important for circulations smaller than the mid-latitude cyclone.

Frictional deceleration

The last force that can influence moving air is frictional deceleration. Friction can exert an influence on wind only after the air is in motion. Frictional drag acts in a direction opposite to the path of motion causing the moving air to decelerate (see Newton’s first and second laws of motion). Frictional effects are limited to the lower one kilometer above the Earth’s surface.

3 General circulation of the atmosphere

The circulation of wind in the atmosphere is driven by the rotation of the earth and the incoming energy from the sun. The winds are driven by the energy from the sun at the surface as warm air rises and colder air sinks. Wind circulates in each hemisphere in three distinct cells which help transport energy and heat from the equator to the poles. These cells are as follows:

• Hadley cell
• Ferrel Cell
• Polar circulations
• Other Important circulations are as follows:
• Walker Circulation
• Jet Streams

The circulation cell closest to the equator is called the Hadley cell. Winds are light at the equator because of the weak horizontal pressure gradients located there. The warm surface conditions result in locally low pressure. The warm air rises at the equator producing clouds and causing instability in the atmosphere. This instability causes thunderstorms to develop and release large amounts of latent heat. Latent heat is just energy released by the storms due to changes from water vapor to liquid water droplets as the vapor condenses in the clouds, causing the surrounding air to become more warm and moist, which essentially provides the energy to drive the Hadley cell.

Hadley cell

The Hadley Cell encompasses latitudes from the equator to about 30°. At this latitude surface high pressure causes the air near the ground to diverge. This forces air to come down from aloft to “fill in” for the air that is diverging away from the surface high pressure. The air flowing northward from the equator high up in the atmosphere is warm and moist compared to the air nearer the poles. This causes a strong temperature gradient between the two different air masses and a jet stream results. At the 30° latitudes, this jet is known as the subtropical jet stream which flows from west to east in both the Northern and Southern Hemispheres. Clear skies generally prevail throughout the surface high pressure, which is where many of the deserts are located in the world.

From 30° latitude, some of the air that sinks to the surface returns to the equator to complete the Hadley Cell. This produces the northeast trade winds in the Northern Hemisphere and the southeast trades in the Southern Hemisphere. The Coriolis force impacts the direction of the wind flow. In the Northern Hemisphere, the Coriolis force turns the winds to the right. In the Southern Hemisphere, the Coriolis force turns the winds to the left.

Ferrel Cell

• From 30° latitude to 60° latitude, a new cell takes over known as the Ferrel Cell. This cell produces prevailing westerly winds at the surface within these latitudes. This is because some of the air sinking at 30° latitude continues traveling northward toward the poles and the Coriolis force bends it to the right (in the Northern Hemisphere). This air is still warm and at roughly 60° latitude approaches cold air moving down from the poles. With the converging air masses at the surface, the low surface pressure at 60° latitude causes air to rise and form clouds. Some of the rising warm air returns to 30° latitude to complete the Ferrel Cell.
• The two air masses at 60° latitude do not mix well and form the polar front which separates the warm air from the cold air. Thus the polar front is the boundary between warm tropical air masses and the colder polar air moving from the north. (The use of the word “front” is from military terminology; it is where opposing armies clash in battle.) The polar jet stream aloft is located above the polar front and flows generally from west to east. The polar jet is strongest in the winter because of the greater temperature contrasts than during the summer. Waves along this front can pull the boundary north or south, resulting in local warm and cold fronts which affect the weather at particular locations.

Polar circulations

Above 60° latitude, the polar cell circulates cold, polar air equatorward. The air from the poles rises at 60° latitude where the polar cell and Ferrel cell meet, and some of this air returns to the poles completing the polar cell. Because the wind flows from high to low pressure and taking into account the effects of the Coriolis force, the winds above 60° latitude are prevailing easterlies.

Walker Circulation

In contrast to the Hadley, Ferrel and polar circulations that run along north-south lines, the Walker circulation is an east-west circulation. Over the eastern Pacific Ocean, surface high pressure off the west coast of South America enhances the strength of the easterly trade winds found near the equator. The winds blow away from the high pressure toward lower pressure near Indonesia. Upwelling, the rising of colder water from the deep ocean to the surface, occurs in the eastern Pacific along South America near Ecuador and Peru. This cold water is especially nutrient-rich and is stocked with an abundance of large fish populations. By contrast the water in the western Pacific, near Indonesia, is relatively warm. The air over Indonesia rises because of the surface low pressure located there and forms clouds. This causes heavy precipitation to fall over the western tropical Pacific throughout the year. The air then circulates back aloft towards the region above the surface high pressure near Ecuador and this becomes the Walker circulation. The air sinks at this surface high pressure and is picked up by the strong trade winds to continue the cycle.

On some occasions, the Walker circulation and the trade winds weaken, allowing warmer water to “slosh back” towards the eastern tropical Pacific near South America. You can think of this as blowing a fan over a bathtub full of water. If the fan blows steadily, the water at the side farthest from the fan will tend to pile up downwind. If you suddenly slow the fan down, some of the water that was built up will surge back towards the fan. The warmer water will cover the areas of upwelling, cutting off the flow of nutrients to the fish and animals that live in the eastern Pacific Ocean. This warming of the eastern Pacific Ocean is known as El Niño. The warmer water will also serve as a source for warm, moist air which can aid in the development of heavy thunderstorms over the mass of warm water.

Jet Streams

Jet streams are the major means of transport for weather systems. A jet stream is an area of strong winds ranging from 190-400 km/h that can be thousands of miles long, a couple of hundred miles across and a few miles deep. Jet streams usually sit at the boundary between the troposphere and the stratosphere at a level called the tropopause. This means most jet streams are about 9.6 -14.5 km off the ground. 

The dynamics of jet streams are actually quite complicated, so this is a very simplified version of what creates jets. The basic idea that drives jet formation is this: a strong horizontal temperature contrast, like the one between the North Pole and the equator, causes a dramatic increase in horizontal wind speed with height. Therefore, a jet stream forms directly over the center of the strongest area of horizontal temperature difference, or the front. As a general rule, a strong front has a jet stream directly above it that is parallel to it. jet streams are positioned just below the tropopause (the red lines) and above the fronts, in this case, the boundaries between two circulation cells carrying air of different temperatures.

The two jet streams that directly affect US weather are the polar jet and the subtropical jet. They are responsible for transporting the weather systems that affect us. The polar front is the boundary between the cold North Pole air and the warm equatorial air.

The polar jet sits at roughly 60°N latitude because this is generally where the polar front sits. The subtropical jet is at roughly 30°N latitude.

The subtropical jet is located at 30°N because of the temperature differences between air at mid-latitudes and the warmer equatorial air.

The polar and subtropical jets are both westerly, meaning they come from the west and blow toward the east. Both jets move north and south with the seasons as the horizontal temperature fields across the globe shift with the areas of strongest sunlight.

In the winter the polar jet moves south and becomes stronger because the North Pole gets colder but the equator stays about the same temperature. This increases the temperature contrast and moves the strengthened polar front jet farther south. As you probably have noticed, jet streams are not just straight across, but have a wavy pattern.

In the winter the polar jet moves south and becomes stronger because the North Pole gets colder but the equator stays about the same temperature. This increases the temperature contrast and moves the strengthened polar front jet farther south. As you probably have noticed, jet streams are not just straight across, but have a wavy pattern.

The Tropical Easterly Jet

The Tropical Easterly Jet is upper level easterly wind that starts in late June and continues until early September. This strong flow of air that develops in the upper atmosphere during the Asian monsoon is centred on 15°N, 50-80°E and extends from South-East Asia to Africa. The strongest development of the jet is at about 15 km above the Earth’s surface with wind speeds of up to 40 m/s over the Indian Ocean.

• The Tropical Easterly Jet is upper level easterly wind that starts in late June and continues until early September. This strong flow of air that develops in the upper atmosphere during the Asian monsoon is centred on 15°N, 50-80°E and extends from South-East Asia to Africa. The strongest development of the jet is at about 15 km above the Earth’s surface with wind speeds of up to 40 m/s over the Indian Ocean.
• Tropical Easterly Jet(TEJ) comes into existence quickly after the Subtropical Jet(STJ) has shifted to the north of the Himalayas (Early June).
• TEJ flows from east to west over peninsular India at 6 – 9 km and over the Northern African region.
• The formation of TEJ results in the reversal of upper air circulation patterns High pressure switches to low pressure and leads to the quick onset of monsoon.
• Recent observations have revealed that the intensity and duration of heating of Tibetan Plateau has a direct bearing on the amount of rainfall in India by the monsoons.
• When the summer temperature of air over Tibet remains high for a sufficiently long time, it helps in strengthening the easterly jet and results in heavy rainfall in India.
• The easterly jet does not come into existence if the snow over the Tibet Plateau does not melt. This hampers the occurrence of rainfall in India.
• Therefore, any year of thick and widespread snow over Tibet will be followed by a year of weak monsoon and less rainfall.

4. Classification of Winds

Wind may be classified into three broad categories:

• Primary Winds or Prevailing Winds or Permanent Winds or Planetary Winds
• Secondary Winds or Periodic Winds
• Tertiary Winds or Local Winds

Planetary wind systems which are related to the general arrangement of pressure belts on the earth’s surface.

Secondary winds consists of cyclones and anticyclones, monsoon,

Tertiary winds includes all the local winds which are produced by local causes such as topographical features, sea influences etc. Their impact is visible only in a particular area.

Primary Winds or Prevailing Winds or Permanent Winds or Planetary Winds

Permanent Winds can be classified into three classes:

• Trade Winds
• Westerlies
• Polar easterlies

Trade Winds

• They flow within the region between 30°N and 30°S.
• They flow as the north-eastern trades in the northern hemisphere and the south-eastern trades in the southern hemisphere. This deflection in their ideally expected north-south direction is explained on the basis of Coriolis force and Farrel’s law.
• Trade winds are descending and stable in areas of their origin (sub-tropical high pressure belt), and as they reach the equator, they become humid and warmer after picking up moisture on their way.
• The trade winds from two hemispheres meet at the equator (ITCZ), and due to convergence they rise and cause heavy rainfall.

• The eastern parts of the trade winds associated with the cool ocean currents are drier and more stable than the western parts of the ocean.
• They play a part in steering the flow of tropical cyclones that develop above the world’s oceans.

The westerlies (blue) and trade winds (yellow and brown)

Westerlies

The Westerlies are the winds in the middle latitudes in the ranges of 35 to 65 degrees. These winds blow from the west to the east and determine the travelling directions of extratropical cyclones in a similar direction.

The winds are mainly from the northwest in the Southern Hemisphere and southwest in the Northern Hemisphere.

The westerlies of the southern hemisphere are stronger and persistent due to the vast expanse of water, while those of the northern hemisphere are irregular because of uneven relief of vast land-masses.

The westerlies are best developed between 40° and 65°S latitudes.

The Westerlies are most powerful in the winter when the pressure is lower over the poles and weakest during the summer when pressure over the poles is higher.

These latitudes are often called Roaring Forties, Furious Fifties, and Shrieking Sixties – dreaded terms for sailors.

The poleward boundary of the westerlies is highly fluctuating. There are many seasonal and short-term fluctuations. These winds produce wet spells and variability in weather.

Consider the following statements about the ‘Roaring Forties’:[2000]
1.They blow uninterrupted in the northern and Southern Hemispheres
2.They blow with great strength and constancy
3.Their direction is generally from north-west to east in the Southern Hemisphere
4.Overcast skies, rain and raw weather are generally associated with them
Which of these statements are correct? (a)1, 2 and 3 (b)2, 3 and 4 (c)1, 3 and 4 (d)1, 2 and 4
Ans. (b)The westerlies in the southern hemisphere is called as roaring forties; lies between 40°S to 50°S and is a permanent wind. It is slow over landmass.

87. Westerlies in southern hemisphere are stronger and persistent than in northern hemisphere. Why ?[2011 – I] 1. Southern hemisphere has less landmass as compared to northern hemisphere. 2. Coriolis force is higher in southern hemisphere as compared to northern hemisphere. Which of the statements given above is/are correct ? (a)1 only (b)2 only (c)Both 1 and 2 (d)Neither 1 nor 2
Ans. 87.(a)The speed of these winds are higher and persistence in southern hemisphere. The land mass in southern hemisphere is lesser in comparison to northern hemisphere. As these winds crosses the landmass its velocity decreases. Thus the effect of westerlies is less over northern hemisphere than in southern hemisphere.

103.Consider the following statements[2015 – I] 1.The winds which blow between 30° N and 60° S latitudes throughout the year are known as westerlies. 2.The moist air masses that cause winter rains in North-Western region of India are part of westerlies. Which of the statements given above is/are correct? (a)1 only (b)2 only (c)Both 1 and 2 (d)Neither 1 nor 2
Ans. 103.(c)The Westerlies are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and tend towards the poles and steer extra tropical cyclones in this general manner. The moist air masses that cause winter rains in North-Western region of India are part of westerlies.

Polar easterlies

The Polar easterlies are dry, cold prevailing winds blowing from north-east to south-west direction in Northern Hemisphere and south-east to north-west in Southern Hemisphere.

They blow from the polar high-pressure areas of the sub-polar lows.

Doldrums

Doldrums are a belt of calms and light winds between the northern and southern trade winds of the Atlantic and Pacific. They occur along a very low pressure area around the equator where the prevailing winds are calmest. Doldrums occur as a result of constant sun’s radiation.

Secondary Winds or Periodic Winds

These winds change their direction with change in season.

Monsoons are the best example of large-scale modification of the planetary wind system.

Other examples of periodic winds include land and sea breeze, mountain and valley breeze, cyclones and anticyclones, and air masses.

Monsoons

Monsoons are seasonal wind in southern Asia.

During summer, the trade winds of southern hemisphere are pulled northwards by an apparent northward movement of the sun and by an intense low pressure core in the north-west of the Indian sub­continent.

While crossing the equator, these winds get deflected to their right under the effect of Coriolis force.

These winds now approach the Asian landmass as south-west monsoons. Since they travel a long distance over a vast expanse of water, by the time they reach the south-western coast of India, they are over-saturated with moisture and cause heavy rainfall in India and neighboring countries.

During winter, these conditions are reversed and a high pressure core is created to the north of the Indian subcontinent. Divergent winds are produced by this anticyclonic movement which travels southwards towards the equator. This movement is enhanced by the apparent southward movement of the sun. These are north-east or winter monsoons which are responsible for some precipitation along the east coast of India.

The monsoon winds flow over India, Pakistan, Bangladesh, Myanmar (Burma), Sri Lanka, the Arabian Sea, Bay of Bengal, south­eastern Asia, northern Australia, China and Outside India, in the eastern Asiatic countries, such as China and Japan, the winter monsoon is stronger than the summer monsoon. (we will study about monsoons in detail while studying Indian Climate)

Sea Breeze and Land Breeze

Sea Breeze – A sea breeze or onshore breeze is any wind that blows from a large body of water toward or onto a landmass; it develops due to differences in air pressure created by the differing heat capacities of water and dry land. As such, sea breezes are more localised than prevailing winds.

Land Breeze – During Night rapidly cooling land soon has a higher air pressure over it relative to that over the sea, and the air begins to flow down the pressure gradient seaward. Unlike the sea breeze, the land breeze is usually weaker in velocity and less common. the land breeze can penetrate the marine atmosphere for 10 kilometres (6 miles) seaward.

Valley Breeze and Mountain Breeze

Valley Breeze (Anabatic Winds) – During the day, the sun heats up mountain air rapidly while valley remains relatively cooler. Convection causes it to rise, causing a valley breeze.

Mountain Breeze (katabatic wind) – During the night the slopes get cooled and the dense air descends into the valley as the mountain wind. The cool air, of the high plateaus and ice fields draining into the valley is called katabatic wind.

Tertiary Winds or Local Winds

Local winds are the ordinary winds. They are influenced by various landforms such as vegetation, hill, plains, water bodies, mountains and so on. The blow variedly and the changes are because of different temperatures and pressure regions during the night and day.

Loo

The Loo is a strong, dusty,gusty, hot and dry summer wind from the west which blows over the western Indo-Gangetic Plain region of North India and Pakistan. It is especially strong in the months of May and June.. It is known as Its temperature invariably ranges between 45°C and 50°C. It may cause sunstroke to people.

Foehn or Fohn

It is a type of dry, warm, down-slope wind that occurs in the lee (downwind side) of a mountain range.

The temperature of the wind varies between 15°C and 20°C. The wind helps animal grazing by melting snow and aids the ripening of grapes.

Foehn winds are traditionally associated with a low pressure area to the south-west of the Alps. The cyclonic winds head into the Alps and Pyrenees from the Mediterranean Sea. A Foehn wind is a warm, dry wind that blows down the lee (sheltered side) of mountains. Note that in the Savoie it is particuarly associated with a wind that blows over the Petit-St Bernard Pass from Italy and down the Tarentaise valley. Anyone who has skied at la Rosiere will know the strength of this wind.

Chinook

Chinook winds are föhn winds in the interior West of North America, where the Canadian Prairies and Great Plains meet various mountain ranges, although the original usage is in reference to wet, warm coastal winds in the Pacific Northwest

Chinook winds have been observed to raise winter temperature, often from below −20 °C (−4 °F) to as high as 10–20 °C (50–68 °F) for a few hours or days, then temperatures plummet to their base levels.

Sirocco

It arises from a warm, dry, tropical airmass that is pulled northward by low-pressure cells moving eastward across the Mediterranean Sea, with the wind originating in the Arabian or Sahara deserts. The hotter, drier continental air mixes with the cooler, wetter air of the maritime cyclone, and the counter-clockwise circulation of the low propels the mixed air across the southern coasts of Europe.

Sirocco is inhibiting substantially different characteristics and has many different local names, too. Along the northern African coast the hot air originates directly from the Sahara desert, producing hot, dry and dusty conditions. Visibility becomes very poor and the fine blowing dust might result in danmage to instruments and equipment. On rare occasions the Sirocco is picking up enough dust and sand to produce even sandstorms.However, the term Sirocco is not used in North Africa, where it is called chom (hot) or arifi (thirsty); Simoom in Palestine, Jordan, Syria, and the desert of Arabia; Ghibli (or Chibli, Gibla, Gibleh) in Libya; Chili (or Chichili) in Tunisia and S Algeria; Khamsin (or Chamsin, Khamasseen) in Egypt and around the Red Sea and Sharavin Israel.

Mistral

Strong, cold, dry and squally northerly wind that blows offshore with great frequency along the Mediterranean coast from northern Spain to northern Italy, and that is particularly frequent in the lower Rhone valley in south-eastern France blowing way out into the Golfe du Lion. The wind may persist for several days, and is best developed when a depression is forming in the Gulf of Genoa to the east of a ridge of high pressure. It might also be a purely katabatic wind. The airstream that feeds the mistral is commonly derived from polar air of maritime origin. It is most violent in winter and spring and its strenght is increased by the funneling effect of the Rhone valley.

Bora

Location: The Adriatic coast of the Balkans

The bora is a cold and typically very dry and often gusty katabatic wind (fall-wind) from the north-east. Bora winds can occur anytime during the year. However, the peak frequency occurs in the cold season (November – March). In general, the frequency of gale force bora winds varies from one day per month, or less, in the summer to six days per month during winter months. The term bora derives from boreas, the north. In other areas it is used as a generic term for cold squalls moving downhill from uplands.

Brickfielder

Location: Australia

The Brickfielder is a strong, hot, dry and dusty wind in southern Australia. The Brickfielder usually occurs during summer and is mainly affecting southeast Australia’s states of Victoria and New South Wales. The Brickfielder is associated with the passage of a frontal zone of a low pressure. Preceding the passage of the front tropical, hot, dry north-westerly desert air from the interior of Australia is carrying clouds of dust and bringing sudden hot spells, often exceeding 38C (100F), to areas which normally have a much milder climate. The temperature might jump up 15 to 20 °C within hours.

Buran or Burga

Location: Central Asia, Siberia and Alaska

A strong cold north-easterly wind creating extreme blizzard conditions during winter. The Buran occurs most frequently in Mongolia and Siberia and Buran winds are are strong and full of ice and snow. The skies is often laden with snow which swirls about and reduces the visibility to near zero at times.

picture This Buran is much feared in the region and can be persistent and close passes for weeks as it blows. Over the tundra it is also known as Purga . In Alaska this severe north-easterly wind is known as Burga bringing snow and ice pellets.

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Air Masses, Fronts & Cyclones

Air Masses

• An air mass is a large mass of air that has similar characteristics of temperature and humidity within it.
• An air mass acquires these characteristics above an area of land or water known as its source region.
• When the air mass sits over a region for several days, or longer, it picks up the distinct temperature and humidity characteristics of that region.

Characteristics

• It must be large. A typical air mass is more than 1600 kilometres across and several kilometres deep.
• At any given altitude in the air mass, its physical characteristics primarily temperature, humidity, and stability are relatively homogeneous.
• It must be distinct from the surrounding air, and when it moves, it must retain its original characteristics and not be torn apart by differences in airflow.

Origin

• Most air masses, then, form most commonly in areas with anticyclonic conditions.
• The formation of air masses is normally associated with what are called source regions.
• Such regions must be extensive, physically uniform, and associated with air that is stationary or anticyclonic.

Classification

Air masses are classified on weather maps using two or three letters.

• A lowercase letter describes the amount of moisture in the air mass: m for maritime (moist) and c for continental (dry).
• An uppercase letter describes the heat of the air mass: E for equatorial, T for tropical, M for monsoon, P for polar, A for Arctic or Antarctic, and S for superior—a unique situation with dry air formed by a powerful downward motion of the atmosphere.
• A lowercase letter describes the relationship between the air mass and the earth: k signifies that the air mass is colder than the ground below it, while w describes an air mass that is warmer than the ground below it.

Fronts

• When two different type of air masses meet, the boundary zone b/w them is called a front.
• Fronts are the typical features of midlatitudes weather (temperate region – 30° – 65° N and S). They are uncommon (unusual) in tropical and polar regions.
• Process of its formation is known as frontogenesis.
• Frontolysis involves overriding of one of the air mass by another.

1. cold front; 2. warm front; 3. stationary front; 4. occluded front; 5. surface trough; 6. squall/shear line; 7. dry line; 8. tropical wave; 9. trowal

Warm Front

Warm front- a front in which warm air replaces cooler air at the surface.

Some of the characteristics of warm fronts include the following:

• The slope of a typical warm front is 1:200 (more gentle than cold fronts).
• Warm fronts tend to move slowly.
• Warm fronts are typically less violent than cold fronts.
• Although they can trigger thunderstorms, warm fronts are more likely to be associated with large regions of gentle ascent (stratiform clouds and light to moderate continuous rain).
• Warm fronts are usually preceded by cirrus first (1000 km ahead), then altostratus or altocumulus (500 km ahead), then stratus and possibly fog.
• Behind the warm front, skies are relatively clear (but change gradually).
• Warm fronts are associated with a frontal inversion (warm air overrunning cooler air).

If a warm front exists on a weather map, it will be northeast of the cold front and often, to the east of a surface low pressure area.

Clouds and precipitation are quite prevalent to the north of the warm front.

This results from the fact that low-level southerly winds in the “warm sector” of the cyclone rise up and over the cooler, more dense air at the surface located north of the warm front. The lifting leads to saturation, cloud formation, and, ultimately, to some form of precipitation.

In Oklahoma, warm fronts are rare in the winter and non-existent in the summer.

Cold Front

Cold front- a front in which cold air is replacing warm air at the surface.

Some of the characteristics of cold fronts include the following:

• The slope of a typical cold front is 1:100 (vertical to horizontal).
• Cold fronts tend to move faster than all other types of fronts.
• Cold fronts tend to be associated with the most violent weather among all types of fronts.
• Cold fronts tend to move the farthest while maintaining their intensity.
• Cold fronts tend to be associated with cirrus well ahead of the front, strong thunderstorms along and ahead of the front, and a broad area of clouds immediately behind the front (although fast moving fronts may be mostly clear behind the front).
• Cold fronts can be associated with squall lines (a line of strong thunderstorms parallel to and ahead of the front).

In winter, cold fronts move into Oklahoma mainly from the Canadian prairies but sometimes from the Arctic Circle or the eastern Pacific.

 Cold fronts almost always are easier to locate on a weather map than are warm fronts, primarily because of the strength of the high pressure system to the north and west of the cold front compared to that north of a warm front.

 Cold fronts usually bring cooler weather, clearing skies, and a sharp change in wind direction.

Stationary front

Stationary front- a front that does not move or barely moves.

Stationary fronts behave like warm fronts, but are more quiescent.

Many times the winds on both sides of a stationary front are parallel to the front.

Typically stationary fronts form when polar air masses are modified significantly so as to lose their character (e.g., cold fronts which stall).

Occluded Front

• When a cold front overtakes a warm front & lift it off from the surface of the earth
• After occlusion, air masses loses their earlier characteristics & form new fronts.
• Meeting of warm & cold air masses in temperate zone gives birth to temperate cyclones along the fronts of warm & cold air masses
• In each case, precipitation is likely to occur but more in case of cold front.

Weather along fronts

Along Cold Front

• The weather along such a front depends on a narrow band of cloudiness and precipitation.
• Severe storms can occur. During the summer months thunderstorms are common in warm sector.
• In some regions like USA tornadoes occur in warm sector.
• Produce sharper changes in weather. Temperatures can drop more than 15 degrees within the first hour.
• The approach of a cold front is marked by increased wind activity in warm sector and the appearance of cirrus clouds, followed by lower, denser altocumulous and
• At actual front, dark nimbus and cumulonimbus clouds cause heavy showers.
• A cold front passes off rapidly, but the weather along it is violent.

Along warm Front

• As the warm air moves up the slope, it condenses and causes precipitation but, unlike a cold front, the temperature and wind direction changes are gradual.
• Such fronts cause moderate to gentle precipitation over a large area, over several hours.
• The passage of warm front is marked by rise in temperature, pressure and change in weather.
• With the approach, the hierarchy of clouds is—-cirrus, stratus and nimbus. [No cumulonimbus clouds as the gradient is gentle]
• Cirrostratus clouds ahead of the warm front create a halo around sun and moon.

Along occluded front

• Weather along an occluded front is complex—a mixture of cold front type and warm front type weather. Such fronts are common in west Europe.
• The formation Mid-latitude cyclones [temperate cyclones or extra-tropical cyclones] involve the formation of occluded front.
• A combination of clouds formed at cold front and warm front.
• Warm front clouds and cold front clouds are on opposite side of the occlusion.

Cyclone

• A cyclone is a system of winds rotating counterclockwise in the Northern Hemisphere around a low pressure center. The swirling air rises and cools, creating clouds and precipitation.
• There are two types of cyclones: middle latitude (mid-latitude) cyclones and tropical cyclones. Mid-latitude cyclones are the main cause of winter storms in the middle latitudes. Tropical cyclones are also known as hurricanes.
• It can be circular, elliptical or ‘V’ shape.
• Mid-latitude cyclones, sometimes called extratropical cyclones, form at the polar front when the temperature difference between two air masses is large. These air masses blow past each other in opposite directions.
• Coriolis Effect deflects winds to the right in the Northern Hemisphere, causing the winds to strike the polar front at an angle. Warm and cold fronts form next to each other.
• Most winter storms in the middle latitudes, including most of the United States and Europe, are caused by mid-latitude cyclones.The warm air at the cold front rises and creates a low pressure cell. Winds rush into the low pressure and create a rising column of air.
• The air twists, rotating counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Since the rising air is moist, rain or snow falls.

Mid-Latitude Cyclones

• Mid-latitude cyclones form in winter in the mid-latitudes and move eastward with the westerly winds. These two- to five-day storms can reach 1,000 to 2,500 km (625 to 1,600 miles) in diameter and produce winds up to 125 km (75 miles) per hour.
• Like tropical cyclones, they can cause extensive beach erosion and flooding.Mid-latitude cyclones are especially fierce in the mid-Atlantic and New England states where they are called nor’easters, because they come from the northeast. About 30 nor’easters strike the region each year.

Tropical cyclones

• Tropical cyclones have many names. They are called hurricanes in the North Atlantic and eastern Pacific oceans.
• Typhoons in the western Pacific Ocean. Tropical cyclones in the Indian Ocean. Willi-willi’s in the waters near Australia.
• Hurricanes arise in the tropical latitudes (between 10 degrees and 25 degrees N) in summer and autumn when sea surface temperature are 28 degrees C (82 degrees F) or higher.
• The warm seas create a large humid air mass. The warm air rises and forms a low pressure cell, known as a tropical depression. Thunderstorms materialize around the tropical depression.
• If the temperature reaches or exceeds 28 degrees C (82 degrees F) the air begins to rotate around the low pressure (counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere).

Willy Willy (1995)
(a) a type of tree grown in temperate regions
(b) a wind that blows in a desert
(c) a tropical cyclone of the north west Australia
(d) a kind of common fish found near Laccadives Islands
Ans. c

Types of Tropical Cyclone – Tropical cyclone are divided into 4 major types:

(1)Tropical disturbance (2) Tropical depression (3) Tropical storms (4) Hurricane or typhoon

1. Tropical disturbance

It is associated with easterly trade winds. The easterly wave develops between 50 to 200 N latitude in the western part of the oceans. It is associated with large amount of cumulus or cumulonimbus cloud. These clouds bring heavy to moderate rainfall.

2. Tropical Depression

This region is the center of low pressure and characterized by closed isobars, which are small in size. The wind velocity at the center is 40-50 km/hr. It is usually influenced by summer weather of India and Australia. Sometimes, it becomes strong and gives heavy rainfall, further resulting in floods.

3. Tropical Storm

Tropical storm is related with low pressure center, closed isobars which rushes towards the center with the velocity ranging between 40 to 120 km/hr. Generally, it develops over Caribbean Sea, near Philippines and Bay of Bengal causing devastation of lives and properties in the coastal regions.

4. Hurricane or Typhoon

It is a form of massive tropical cyclone surrounded by several closed isobars. It moves with an average speed of 120 km?

Hurricane has more symmetrical and circular isobars. The pressure increases sharply from Centre towards the outer margin, resulting in pressure gradient. Heavy downpour occurs, which is often uniformly distributed over a larger area as compared to other types of tropical cyclones.

As the air rises, water vapor condenses, releasing energy from latent heat. If wind shear is low, the storm builds into a hurricane within two to three days.Hurricanes are huge with high winds. The exception is the relatively calm eye of the storm where air is rising upward. Rainfall can be as high as 2.5 cm (1″) per hour, resulting in about 20 billion metric tons of water released daily in a hurricane. The release of latent heat generates enormous amounts of energy, nearly the total annual electrical power consumption of the United States from one storm. Hurricanes can also generate tornadoes.

Hurricanes are huge with high winds. The exception is the relatively calm eye of the storm where air is rising upward. Rainfall can be as high as 2.5 cm (1 inch) per hour, resulting in about 20 billion metric tons of water released daily in a hurricane. The release of latent heat generates enormous amounts of energy, nearly the total annual electrical power consumption of the United States from one storm. Hurricanes can also generate tornadoes.Hurricanes are strange creatures because they are deadly monsters, yet have a gentle, but cold heart. The anatomy of a hurricane is fairly simple, though the processes involved are quite complex. As a low pressure disturbance forms, the warm, moist air rushes towards the low pressure in order to rise upward to form towering thunderstorms. Around the low pressure disturbance is a wall of clouds called an eye wall. Within the eye wall, the wind speeds are greatest, the clouds are the tallest, atmospheric pressure is at its lowest, and precipitation is most intense.

At the center or heart of the hurricane is called the eye. Within the eye of a hurricane, winds are light, precipitation is minimal, and occasionally the skies above are clear. It is the calm region of the tropical storm, but that is what makes it so dangerous. Many people tend to go outside as the eye moves overhead because they believe the storm is over. But what some don’t realize is that “round two” is coming from behind.

Hurricanes are assigned to categories based on their wind speed. The categories are listed on the Saffir-Simpson Scale.

Hurricanes move with the prevailing winds. In the Northern Hemisphere, they originate in the trade winds and move to the west. When they reach the latitude of the westerlies, they switch direction and travel toward the north or northeast. Hurricanes may cover 800 km (500 miles) in one day.Damage from hurricanes comes from the high winds, rainfall, and storm surge. Storm surge occurs as the storm’s low pressure center comes onto land, causing the sea level to rise unusually high. A storm surge is often made worse by the hurricane’s high winds blowing seawater across the ocean onto the shoreline. Flooding can be devastating, especially along low-lying coastlines such as the Atlantic and Gulf Coasts. Hurricane Camille in 1969 had a 7.3 m (24 foot) storm surge that traveled 125 miles (200 km) inland.

Hurricanes typically last for 5 to 10 days. Over cooler water or land, the hurricane’s latent heat source shut downs and the storm weakens. When a hurricane disintegrates, it is replaced with intense rains and tornadoes.

There are about 100 hurricanes around the world each year, plus many smaller tropical storms and tropical depressions. As people develop coastal regions, property damage from storms continues to rise. However, scientists are becoming better at predicting the paths of these storms and fatalities are decreasing. There is, however, one major exception to the previous statement: Hurricane Katrina.

Blizzards and Lake Effects

A blizzard is distinguished by certain conditions:

Temperatures below –7 degrees C (20 degrees F); –12oC (10 degrees F) for a severe blizzard.

Winds greater than 56 kmh (35 mph); 72 kmh (45 mph) for a severe blizzard.

Snow so heavy that visibility is 2/5 km (1/4 mile) or less for at least three hours; near zero visibility for a severe blizzard.

• Blizzards happen across the middle latitudes and toward the poles, usually as part of a mid-latitude cyclone. Blizzards are most common in winter, when the jet stream has traveled south and a cold, northern air mass comes into contact with a warmer, semi tropical air mass. The very strong winds develop because of the pressure gradient between the low pressure storm and the higher pressure west of the storm.
• In winter, a continental polar air mass travels down from Canada. As the frigid air travels across one of the Great Lakes, it warms and absorbs moisture. When the air mass reaches the leeward side of the lake, it is very unstable and it drops tremendous amounts of snow. This lake-effect snow falls on the snowiest, metropolitan areas in the United States: Buffalo and Rochester, New York.

in contrast to depressions, anticyclones only involve one type of air mass which usually cover large areas and do not have any fronts. they are high pressure systems in which the air moves downwards towards the earth’s surface. as the air descends, the molecules become compressed, the pressure increases and it warms. when air is warming, any moisture in the atmosphere is evaporated so no clouds can form. the sky is clear. anticyclones can be very large, typically at least 3,000 km wide. once they become established, they can give several days of settled weather. winds are very gentle or even calm in an anticyclone, move clockwise, and this is shown on a synoptic chart by wide spaced isobars.

Assertion (A) : The surface winds spiral inwards upon the centre of the cyclone.
Reason (R) : Air descends in the centre of the cyclone.[2002]
(a)Both A and R are true and R is the correct explanation of A (b)Both A and R are true but R is NOT a correct explanation of A (c)A is true but R is false (d) A is false but R is true
Ans. (a)Air begins to slowly descend in the centre of the storm, creating a rain-free area. This is a newly formed eye. On land,, the centre of the eye is, by for, the calmest part of the storm.
62.Assertion (A) : Wind patterns are clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere. Reason (R) : The directions of wind patterns in the Northern and the Southern Hemisphere are governed by the Coriolis effect.[2005] (a)Both A and R are true and R is the correct explanation of A (b)Both A and R are true but R is NOT a correct explanation of A (c)A is true but R is false (d)A is false but R is true
Ans. 62.(a)A is true as the direction of wind in the northern hemisphere is clock wise and in southern hemisphere it is anti clock wise. The explanation is correct as this is mainly due to coriolis effect.
Which one of the following weather conditions is indicated by a sudden fall in barometer reading?
(a) Stormy[2001] (b)Calm weather (c)Cold and dry weather (d)Hot and sunny weather
Ans. (a)In stormy weather conditions the pressure of the atmosphere varies, which causes sudden fall in barometer reading.
106.In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?[2015 – I] (a)Sea surface temperatures are low (b)Inter-Tropical Convergence Zone seldom occurs (c)Coriolis force is too weak (d)Absence of land in those regions
Ans. 106.(a)

Anticyclones

High-pressure systems are frequently associated with light winds at the surface and subsidence of air from higher portions of the troposphere. Subsidence will generally warm an air mass by adiabatic (compressional) heating. Thus, high pressure typically brings clear skies. Because no clouds are present to reflect sunlight during the day, there is more incoming solar radiation and temperatures rise rapidly near the surface. At night, the absence of clouds means that outgoing longwave radiation (i.e. heat energy from the surface) is not blocked, giving cooler diurnal low temperatures in all seasons. When surface winds become light, the subsidence produced directly under a high-pressure system can lead to a buildup of particulates in urban areas under the high pressure, leading to widespread haze.If the surface level relative humidity rises towards 100 percent overnight, fog can form.

Weather associated with Anticyclone

Hadley cell circulation tends to create anticyclonic patterns in the Horse latitudes, depositing drier air and contributing to the world’s great deserts.

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Precipitation

1. Hydrological Cycle
2. Humidity
3. Evaporation
4. Condensation
5. Precipitation
6. El Nino

1  Hydrological cycle

• The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes the continuous movement of water on, above and below the surface of the Earth.
• The mass of water on Earth remains fairly constant over time but the partitioning of the water into the major reservoirs of ice, fresh water, saline water and atmospheric water is variable depending on a wide range of climatic variables.
• Water vapour in air varies from zero to four per cent by volume of the atmosphere (averaging around 2% in the atmosphere). Amount of water vapour (Humidity) is measured by, an instrument called Hygrometer.
• Water vapour absorbs radiation—both incoming and terrestrial. It thus plays a crucial role in the earth’s heat budget.
• The amount of water vapour present decides the quantity of latent energy stored up in the atmosphere for development of storms and cyclones.
• The atmospheric moisture affects the human body’s rate of cooling by influencing the sensible temperature.

Humidity is the amount of water vapour present in air. Water vapour, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.

Water

The distribution of water on the Earth’s surface is extremely uneven. Only 3% of water on the surface is fresh; the remaining 97% resides in the ocean. Of freshwater, 69% resides in glaciers, 30% underground, and less than 1% is located in lakes, rivers, and swamps. Looked at another way, only one percent of the water on the Earth’s surface is usable by humans, and 99% of the usable quantity is situated underground.

All one needs to do is study rainfall maps to appreciate how uneven the distribution of water really is. The white areas on the map below had annual rainfall under 400 mm for the last year, which makes them semi-arid or arid. And, remember, projections are for significant aridification to occur in many dry regions and for more severe rainfall events to characterize wet regions.

2. Humidity

Types of Humidity

Absolute humidity

• Absolute humidity is the total mass of water vapor present in a given volume or mass of air. It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly 30 grams per cubic metre when the air is saturated at 30 °C (86 °F).
• The absolute humidity changes as air temperature or pressure changes, if the volume is not fixed.

Relative humidity

• The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.
• Relative Humidity = [Actual amount of water vapor in air (absolute humidity)/humidity at saturation point (the maximum water vapor air can hold at a given temperature)] X 100
• With the change of air temperature, the capacity to retain moisture increases or decreases and the relative humidity is also affected.
• Relative humidity is greater over the oceans and least over the continents (absolute humidity is greater over oceans because of greater availability of water for evaporation).
• Air containing moisture to its full capacity at a given temperature is said to be ‘saturated’. At this temperature, the air cannot hold any additional amount of moisture. Thus, relative humidity of the saturated air is 100%.
• If the air has half the amount of moisture that it can carry, then it is unsaturated and its relative humidity is only 50%.
• Dew point occurs when Relative Humidity = 100%.

Specific Humidity

• It is expressed as the weight of water vapour per unit weight of air.
• Since it is measured in units of weight (usually grams per kilogram), the specific humidity is not affected by changes in pressure or temperature.

3 Evaporation

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase.

Evaporation is a very important part of the water cycle. Heat from the sun, or solar energy, powers the evaporation process. It soaks up moisture from soil in a garden, as well as the biggest oceans and lakes. The water level will decrease as it is exposed to the heat of the sun.

Studies have shown that the oceans, seas, lakes, and rivers provide nearly 90 percent of the moisture in the atmosphere via evaporation, with the remaining 10 percent being contributed by plant transpiration.

Important factors that affect evaporation are :

1. Wind assists evaporation; for example in clothes dry faster under a fan.

2. Heat assists evaporation; for example, in summer clothes dry faster than in winter.

3. Increase in surface area exposed assists evaporation; for instance, a wet cloth spread out dries faster than when folded.

4. Dryness assists evaporation; for instance, clothes dry faster in summer than during the monsoon when the air is humid.

5. Rate of evaporation depends upon the nature of the liquid.

6. Vapor pressure: if pressure is applied on the surface of a liquid, evaporation is hindered; consider, for example, the case of a pressure cooker.

4. Condensation

• Defined as transformation of water vapour into water, caused by loss of heat when moist air is cooled.
• Cooling may reach a level when air’s capacity to hold water vapour ceases, then excess of water vapour condenses into liquid form
• If water vapour directly condenses into solid form, it is known as sublimation
• In free air, condensation results from cooling around very small particles termed as condensation nuclei.
• Particle of dust, smoke & salt from oceans are particularly good nuclei as they absorb water (Hygroscopic nuclei)

Condensation takes place:

• when the temperature of the air is reduced to dew point with its volume remaining constant (adiabatically),
• when both the volume and the temperature are reduced,
• when moisture is added to the air through evaporation,

Processes of Cooling for Producing Condensation

These processes can be studied under the” headings, adiabatic and non-adiabatic.

Adiabatic Temperature Changes

• When the air rises, it expands. Thus, heat available per unit volume is reduced and, therefore, the temperature is also reduced. Such a temperature change which does not involve any subtraction of heat, and cooling of air takes place only by ascent and expansion, is termed ‘adiabatic change’.

Non-Adiabatic Temperature Changes

Non-adiabatic processes include cooling by radiation, conduction or mixing with colder air. The air may be cooled due to loss of heat by radiation.

In case there is direct radiation from moist air, the cooling produces fog or clouds, subject to presence of hygroscopic nuclei in the air.

Forms of Condensation

Dew

Forms when moisture is deposited in form of water droplets on cooler surfaces of solid objects such as stone, glass, blades, plant leaves etc. rather than on nuclei in air above

Forms when temperature of air falls below dew point but above freezing point.

Frost

Forms on solid surfaces when condensation takes place below freezing point i.e. 0*C

Fog & Mist

When temp. of an air mass containing large quantity of water vapour falls all of a sudden, condensation takes place on fine dust & smoke particles

So, fog is basically a cloud with its base at or very near to ground

Only difference b/w fog & mist is that mist contains more moisture than fog & each nuclei in mist contains thicker layer of moisture

Fog is formed generally when warm & cold currents meet

Mist is formed frequently over the mountains when rising warm air up the slopes meet cold surfaces.

Advection fog: Advection fog is fog produced when air that is warmer and more moist than the ground surface moves over the ground surface. The term advection means a horizontal movement of air. Unlike radiation fog, advection fog can occur even when it is windy. Also unlike radiation fog, advection fog can occur when the skies aloft are initially cloudy.

Smog

In urban & industrial areas, smoke provides plenty of nuclei which helps in the formation of fog & mist

Such a condition, when fog is mixed with smoke is called smog

Haze

Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky (No condensation. Smog is similar to haze but there is condensation in smog). Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires.

Clouds

Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations.

Clouds are caused mainly by the adiabatic cooling of air below its dew point.

As the clouds are formed at some height over the surface of the earth, they take various shapes.

According to their height, expanse, density and transparency or opaqueness clouds are grouped under four types : (i) cirrus; (ii) cumulus; (iii) stratus; (iv) nimbus.

Based on the height or altitude the clouds are classified into three. They are –

1. High Clouds
2. Middle Clouds
3. Low Clouds

1) High Clouds

a. Cirrus – Ci

They are thin and often wispy cirrus clouds. Typically found at heights greater than 20,000 feet (6,000 meters), they are composed of ice crystals that originate from the freezing of supercooled water droplets.

b. Cirrostratus – Cs

They are high, very thin, comprises a uniform layer, and are composed of ice-crystals. It is difficult to detect and is capable of forming halos when the cloud takes the form of thin cirrostratus nebulosus.

c. Cirrocumulus – Cc

They are small rounded puffs shaped clouds, that usually appear in long rows high in the sky and are usually white, but sometimes appear grey.

2) Middle Clouds

• They form between 6,500 feet and cirrus level or from 2000 to 6000 metres.
• They are also known as “Alto” clouds.
• They frequently indicate an approaching storm.
• They may sometimes produce Virga, which is a rain or snow that does not reach the ground.

a. Altostratus – As

These clouds are in the form of continuous sheet or veil, grey or blue-gray in colour. They are composed of ice crystals and water droplets. In its thinner areas, the sun can still be visible as a round, dim disk. These clouds may often form ahead of storms with continuous rain or snow.

b. Altocumulus – Ac

They are greyish sheet cloud, characterised by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus.

3) Low Clouds

• They lie below 6,500 feet, which means from the surface to 2,000 meters.
• Low clouds are also known as Stratus Clouds.
• They may appear dense, dark, and rainy (or snowy) and can also be cottony white clumps interspersed with blue sky.

a. Strato Cumulus – Sc

Usually arranged in a large dark, rounded or globular masses, usually in groups, lines, or waves.

b. Stratus – St

Usually looks like a huge grey blanket that hangs low in the sky that resembles fog, comprises uniform layer and appear dull, if these clouds are warm it means rain and if it is cold it snows.

c. Nimbostratus – Ns

They are small rounded puffs shaped clouds, that usually appear in long rows high in the sky and are usually white, but sometimes appear grey.

4) Great Vertical Extent Clouds

• They are most dramatic types of clouds.
• Great Vertical Extent Clouds are also known as the Storm Clouds.
• They rise to dramatic heights, and sometimes well above the level of transcontinental jetliner flights.

a. Cumulus – Cu

They are convection clouds, puffy, that sometimes look like pieces of floating cotton. The base of each cloud is often flat and may be only 1000 meters (3300 feet) above the ground. The top of the cloud has rounded towers.

b. Cumulonimbus – Cb

They are dense towering vertical cloud, it’s top acquiring an ‘Anvil Shape’, associated with thunderstorms and atmospheric instability, forming from water vapour carried by powerful upward air currents.

Consider the following climatic and geographical phenomena:[2002]
1.Condensation 2.High temperature and humidity 3.Orography 4.Vertical wind Thunder cloud development is due to which of these phenomena?
(a)1 and 2 (b)2, 3 and 4 (c)1, 3 and 4 (d)1, 2 , 3 and 4
Ans. (d)The thunder clouds develop by the above climatic and geographic phenomena. High temperature and humidity causes the wind to rise vertically up and due to orography and pressure of mountains these winds get condensed and form cumulonimbus clouds or thunder clouds.

5 Precipitation

• Precipitation is any product of the condensation of atmospheric water vapor that falls under gravity.
• Precipitation is a major component of the water cycle, and is responsible for depositing the fresh water on the planet. Approximately 505,000 cubic kilometres of water falls as precipitation each year.
• Precipitation in the form of drops of water is called rainfall, when the drop size is more than 5 mm.
• The main forms of precipitation include drizzle, rain, sleet, snow, graupel and hail.
• When the temperature is lower than the 0° C, precipitation takes place in the form of fine flakes of snow and is called snowfall.

Forms of Precipitation

• Sleet is frozen raindrops and refrozen melted snow-water. When a layer of air with the temperature above freezing point overlies a sub freezing layer near the ground, precipitation takes place in the form of sleet.
• Drizzle: light rainfall; drop size less than 0.5 mm.
• Mist: evaporation occurs before reaching the ground leading to foggy weather.
• Snowfall: fine flakes of snow fall when the temperature is less than 0°C.
• Sleet: frozen raindrops and refrozen melted snow; mixture of snow and rain.
• Hail: precipitation in the form of hard rounded pellets is known as hail; 5 mm and 50 mm.

Types of Rainfall

• On the basis of origin, rainfall may be classified into three main types – the convectional, orographic or relief and the cyclonic or frontal.

Convectional Rainfall

• The convectional rainfall occurs due to the thermal convection currents caused due to the heating of ground due to insolation.
• The convectional rainfall is prevalent in equatorial regions. In these, the warm air rises up and expands then, reaches at a cooler layer and saturate then condenses mainly in the form of cumulus or cumulonimbus clouds. In the equatorial regions, the precipitation due to convectional rainfall occurs in the afternoon. The rainfall is of very short duration but in the form of heavy showers.

Orographic Rainfall

• This type of precipitation occurs when warm, humid air strikes an orographic barrier (a mountain range) head on. Because of the initial momentum, the air is forced to rise. As the moisture laden air gains height, condensation sets in, and soon saturation is reached. The surplus moisture falls down as orographic precipitation along the windward slopes. Besides taking the moist winds aloft, the orographic barriers (i) chill moist winds by contact with snow capped summits, (ii) obstruct the path of low pressure areas, (iii) cause convection along the slope by differential heating.
• The windward slope of a mountain range gets more precipitation than the leeward slope because the; air moves down the slope and gets warmed up. Hence, the leeward slope is drier and is known as the rain-shadow area. The wide variation in the amount of rainfall at Mahabaleshwar and Pune, only a few kilometres away from each other, is due to the orographic nature of rainfall. Mahabaleshwar, situated on the Western Ghats, receives more than 600 cm of rainfall, whereas Pune, lying in the rainshadow area, has only about 70 cm.

Frontal Precipitation

Frontal Precipitation When two air masses with different temperatures meet, turbulent conditions are produced. Along the front convection occurs and causes precipitation. For instance, in north-west Europe, cold continental air and warm oceanic air converge to produce heavy rainfall in adjacent areas.

Cyclonic Precipitation

Cyclonic Precipitation This type of precipitation is caused when ascent of air takes place due to horizontal convergence of air streams in low pressure cells within a cyclone. The precipitation in a tropical cyclone is of convectional type while that in a temperate cyclone is because of frontal activity.

Monsoonal Precipitation

Monsoonal Precipitation This type of precipitation is characterised by seasonal reversal of winds which carry oceanic moisture (especially the south-west monsoon) with them and cause extensive rainfall in south and Southeast Asia.

Global Distribution 

There is no uniformity of precipitation all over the world. The average annual precipitation for the world is 97.5 centimeters. The land area receives lesser amount of rainfall as compared to oceans while the different places on earth’s surface receive different amount of annual rainfall and also in different seasons.

On the basis of global pressure, wind bells, distribution of land and water bodies and nature of relief feature on earth, the distribution of precipitation can be explained:

1. Regions of Heavy Precipitation: Rainfall more than 200 cm per year are:

(i) Equatorial regions: Amazon and Congo Basins, Malaysia, Indonesia and New Guinea.

(ii) Tropical monsoon regions: Parts of India. South-east Asia and South China.

(iii) Mid-latitude West Margin regions: Coastal regions of British Columbia. North-west Europe, South Chile and South Island of New Zealand.

2. Moderate rainfall (100 to 200 cm per year)

(i) Eastern margins of continents in the trade-wind belt e.g. eastern margin of China, U.S.A., Brazil, South Africa and Australia.

3. Regions of very low rainfall (less than 50 cm.)

(i) Tropical deserts — Western margins of continents in the trade wind belt, Californian desert (USA), Atacama (South America), Kalahari (Southern Africa), Sahara, Arabian Desert and West Australian desert.

(ii) Mid-latitude desert — Interiors of large continents like Asia and North America.

(iii) Polar Regions — Arctic and Antarctic.

Given below are two statements one labelled as Assertion (A) and the other labelled as Reason (R).[1996]
Assertion (A) : Areas near the equator receive rainfall throughout the year.
Reason (R) : High temperatures and high humidity cause convectional rain in most afternoons near the equator.
In the context of the above two statements, which one of the following is correct?
(a)Both A and R are true and R is the correct explanation of A
(b)Both A and R true but R is not a correct explanation of A
(c)A is true but R is false
(d)A is false but R is true
Ans. a
55.Assertion (A) : Areas lying within five to eight degrees latitude on either side of the equator receive rainfall throughout the year. Reason (R) : High temperatures and high humidity cause convectional rain to fall mostly in the afternoons near the equator.[2003] (a)Both A and R are individually true and R is the correct explanation of A (b)Both A and R are individually true but R is not the correct explanation of A (c)A is true but R is false (d)A is false but R is true
Ans. 55.(a)The highest rainfall totals occur near the equator in the tropics, where the strong heating by the sun creates significant vertical uplifts of air and the formation of prolonged heavy showeas and frequent thunderstorms.

Seasonal Variation of Precipitation:

The equatorial regime has two maxima after summer and winter solstices. The tropical regime has a maximum after the summer solstice. The monsoonal regime has a maximum during summer. The Mediterranean regime has a winter maxima and a summer minima. The continental regime has a summer maxima and winter. Minima. The maritime regime along western coasts in temperate zones has a winter maxima.

Diurnal Variation:

The continents have a late morning and early afternoon maxima. The tropics have an afternoon maximum. The .maritime regime has a maximum during night and early morning due to nocturnal convection.

6. Effects of El Niño, La Niña and the Southern Oscillation on precipitation

El Niño is the name given to the occasional development of warm ocean surface waters along the coast of Ecuador and Peru. When this warming occurs the usual upwelling of cold, nutrient rich deep ocean water is significantly reduced. El Niño normally occurs around Christmas and usually lasts for a few weeks to a few months. Sometimes an extremely warm event can develop that lasts for much longer time periods. In the 1990s, strong El Niños developed in 1991 and lasted until 1995, and from fall 1997 to spring 1998.

The formation of an El Niño is linked with the cycling of a Pacific Ocean circulation pattern known as the southern oscillation. In a normal year, a surface low pressure develops in the region of northern Australia and Indonesia and a high pressure system over the coast of Peru . As a result, the trade winds over the Pacific Ocean move strongly from east to west. The easterly flow of the trade winds carries warm surface waters westward, bringing convective storms to Indonesia and coastal Australia. Along the coast of Peru, cold bottom water wells up to the surface to replace the warm water that is pulled to the west.

Global climatological effects of the El Niño.

This cross-section of the Pacific Ocean, along the equator, illustrates the pattern of atmospheric circulation typically found at the equatorial Pacific. Note the position of the thermocline.

This cross-section of the Pacific Ocean, along the equator, illustrates the pattern of atmospheric circulation that causes the formation of the El Niño. Note how position of the thermocline has changed

NASA’s TOPEX/Poseidon satellite is being used to monitor the presence of El Niño. Sensors on the satellite measure the height of the Pacific Ocean.

TOPEX/Poseidon satellite image of a moderate La Niña condition (January, 2000).

In an El Niño year, air pressure drops over large areas of the central Pacific and along the coast of South America . The normal low pressure system is replaced by a weak high in the western Pacific (the southern oscillation). This change in pressure pattern causes the trade winds to be reduced. This reduction allows the equatorial counter current (which flows west to east – see ocean currents map in topic 8q) to accumulate warm ocean water along the coastlines of Peru and Ecuador . This accumulation of warm water causes the thermocline to drop in the eastern part of Pacific Ocean which cuts off the upwelling of cold deep ocean water along the coast of Peru. Climatically, the development of an El Niño brings drought to the western Pacific, rains to the equatorial coast of South America, and convective storms and hurricanes to the central Pacific.

La Niña.

After an El Niño event weather conditions usually return back to normal. However, in some years the trade winds can become extremely strong and an abnormal accumulation of cold water can occur in the central and eastern Pacific . This event is called a La Niña. A strong La Niña occurred in 1988 and scientists believe that it may have been responsible for the summer drought over central North America. The most recent La Niña began developing in the middle of 1998 and was persistent into the winter of 2000. During this period, the Atlantic Ocean has seen very active hurricane seasons in 1998 and 1999. In 1998, ten tropical storm developed of which six become full-blown hurricanes. One of the hurricanes that developed, named Mitch, was the strongest October hurricane ever to develop in about 100 years of record keeping. Some of the other weather effects of La Niña include abnormally heavy monsoons in India and Southeast Asia, cool and wet winter weather in southeastern Africa, wet weather in eastern Australia, cold winter in western Canada and northwestern United States, winter drought in the southern United States, warm and wet weather in northeastern United States, and an extremely wet winter in southwestern Canada and northwestern United States.

For short-term climatic predictions, which one of the following events, detected in the last decade, is associated with occasional weak monsoon rains in the Indian subcontinent?[2002]
(a)La Nina (b)Movement of Jet Stream (c)El Nino. and Southern Oscillations (d)Greenhouse effect at global level
Ans. (c)E1 Nino and La Nina are opposite phases of what is known as the E1 Nino-southern Oscillation (ENSO) cycle. The ENSO cycle is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the east-central. Impact of E1 -Nino: – Normal or High rainfall in Eastern/Central Pacific. – Drought or Scant rainfall in western Pacific/Asia.
79.A new type of El Nino called El Nino Modoki appeared in the news. In this context, consider the following statements:[2010] 1.Normal El Nino forms in the Central Pacific Ocean whereas El Nino Modoki forms in Eastern Pacific Ocean 2.Normal El Nino results in diminished hurricanes in the Atlantic Ocean but El Nino Modoki results in a greater number of hurricanes with greater frequency. Which of the statements given above is/are correct? (a)1 only (b)2 only (c)Both 1 and 2 (d)Neither 1 nor 2
Ans. 79.(b)Normal El Nino forms in south–eastern Pacific whereas as El Nino Modoki forms in central Pacific and causes greater number of hurricanes. 80.(c)The Albedo of Snow is hightest.
85. La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino ? 1.La Nina is characterized by unusually cold ocean temperature in equatorial Indian Ocean whereas El Nino is characterized by unusually warm ocean temperature in the equatorial Pacific Ocean. 2. El Nino has adverse effect on south-west monsoon of India, but La Nina has no effect on monsoon climate.[2011 – I] Which of the statements given above is/are correct? (a)1 only (b)2 only (c)Both 1 and 2 (d)Neither 1 nor 2
Ans. 85. (d)

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World Climates

Climatic Regions

The Köppen Climate Classification System is the most widely used system for classifying the world’s climates. Its categories are based on the annual and monthly averages of temperature and precipitation. The Köppen system recognizes five major climatic types; each type is designated by a capital letter.

A – Tropical Moist Climates: all months have average temperatures above 18° Celsius.

B – Dry Climates: with deficient precipitation during most of the year.

C – Moist Mid-latitude Climates with Mild Winters.

D – Moist Mid-Latitude Climates with Cold Winters.

E – Polar Climates: with extremely cold winters and summers.

Tropical Moist Climates (A)

Tropical moist climates extend northward and southward from the equator to about 15 to 25° of latitude. In these climates all months have average temperatures greater than 18° Celsius. Annual precipitation is greater than 1500 mm.

Three minor Köppen climate types exist in the A group, and their designation is based on seasonal distribution of rainfall.

• Af or tropical wet is a tropical climate where precipitation occurs all year long. Monthly temperature variations in this climate are less than 3° Celsius. Because of intense surface heating and high humidity, cumulus and cumulonimbus clouds form early in the afternoons almost every day. Daily highs are about 32° Celsius, while night time temperatures average 22° Celsius.
• Am is a tropical monsoon climate. Annual rainfall is equal to or greater than Af, but most of the precipitation falls in the 7 to 9 hottest months. During the dry season very little rainfall occurs.
• The tropical wet and dry or savanna (Aw) has an extended dry season during winter. Precipitation during the wet season is usually less than 1000 millimeters, and only during the summer season.

Dry Climates (B)

The most obvious climatic feature of this climate is that potential evaporation and transpiration exceed precipitation. These climates extend from 20 – 35° North and South of the equator and in large continental regions of the mid-latitudes often surrounded by mountains. Minor types of this climate include:

• BW – dry arid (desert) is a true desert climate. It covers 12% of the Earth’s land surface and is dominated by xerophytic vegetation. The additional letters h and k are used generally to distinguish whether the dry arid climate is found in the subtropics or in the mid-latitudes, respectively.
• BS – dry semiarid (steppe). Is a grassland climate that covers 14% of the Earth’s land surface. It receives more precipitation than the BW either from the intertropical convergence zone or from mid-latitude cyclones. Once again, the additional letters h and k are used generally to distinguish whether the dry semiarid climate is found in the subtropics or in the mid-latitudes, respectively.

Moist Subtropical Mid-Latitude Climates (C)

This climate generally has warm and humid summers with mild winters. Its extent is from 30 to 50° of latitude mainly on the eastern and western borders of most continents. During the winter, the main weather feature is the mid-latitude cyclone. Convective thunderstorms dominate summer months. Three minor types exist: Cfa – humid subtropical; Cs – Mediterranean; and Cfb – marine. The humid subtropical climate (Cfa) has hot muggy summers and frequent thunderstorms. Winters are mild and precipitation during this season comes from mid-latitude cyclones. A good example of a Cfa climate is the southeastern USA. Cfb marine climates are found on the western coasts of continents. They have a humid climate with short dry summer. Heavy precipitation occurs during the mild winters because of the continuous presence of mid-latitude cyclones. Mediterranean climates (Cs) receive rain primarily during winter season from the mid-latitude cyclone. Extreme summer aridity is caused by the sinking air of the subtropical highs and may exist for up to 5 months. Locations in North America are from Portland, Oregon to all of California.

Moist Continental Mid-latitude Climates (D)

Moist continental mid-latitude climates have warm to cool summers and cold winters. The location of these climates is pole ward of the C climates. The average temperature of the warmest month is greater than 10° Celsius, while the coldest month is less than -3° Celsius. Winters are severe with snowstorms, strong winds, and bitter cold from Continental Polar or Arctic air masses. Like the C climates there are three minor types: Dw – dry winters; Ds – dry summers; and Df – wet all seasons.

Polar Climates (E)

Polar climates have year-round cold temperatures with the warmest month less than 10° Celsius. Polar climates are found on the northern coastal areas of North America, Europe, Asia, and on the landmasses of Greenland and Antarctica. Two minor climate types exist. ET or polar tundra is a climate where the soil is permanently frozen to depths of hundreds of meters, a condition known as permafrost. Vegetation is dominated by mosses, lichens, dwarf trees and scattered woody shrubs. EF or polar ice caps has a surface that is permanently covered with snow and ice.

Climatic Region Descriptions

The following discussion organizes the climatic regions of the world into eight different groups. Categorization of these climates is based on their Köppen classification and seasonal dominance of air masses.

Tropical Wet

Köppen Classification – Af.

Dominated by Maritime Tropical air masses all year long.

The tropical wet climate is characterized by somewhat consistent daily high temperatures ranging between 20 to 30° Celsius. The monthly temperature averages vary from 24 to 30° Celsius. Annual range of monthly temperatures is about 3° Celsius. It has reasonably uniform precipitation all year round, and total rainfall over 2000 millimeters or greater.

The region experiencing this climate lies within the effects of the intertropical convergence zone all year long. Convergence and high maritime humidity creates cumulus clouds and thunderstorms almost daily.

Af – Iquitos, Peru 4° S , Elevation: 104 m

Consider the following statements:[2002]
1.In equatorial regions, the year is divided into four main seasons
2.In Mediterranean region, summer months receive more rain.
3.In China type climate; rainfall occurs throughout the year
4.Tropical highlands exhibit vertical zonation of different climates Which of these statements are correct? (a)1, 2, 3 and 4 (b)1, 2 and 3 (c)1, 2 and 4 (d)3 and 4
Ans. (d)1st statement is wrong: The Equatorial region has only two seasons. 2nd statement : Mediterranean gets rainfall during winter season is also wrong.
93.Which one of the following is the characteristic climate of the Tropical Savannah Region?[2012 – I] (a)Rainfall throughout the year (b)Rainfall in winter only (c)An extremely short dry season (d)A definite dry and wet season
Ans. 93.(d)Savannah covers approximately 20% of the Earth’s land area. The largest area of Savannah is in Africa. The tropical Savannah region has a definite dry and wet season. Savannah grasslands are much richer in humus than the equatorial forests.
105.”Each day is more or less the same, the morning is clear and bright with a sea breeze; as the Sun climbs high in the sky, heat mounts up, dark clouds form, then rain comes with thunder and lightning. But rain is soon over.” Which of the following regions is described in the above passage?[2015 – I] (a)Savannah (b)Equatorial (c)Monsoon (d)Mediterranean
Ans. 105. (b)The passage points out equatorial region.

Tropical Wet and Dry
Köppen Classification – Aw and Am.

• • Maritime Tropical air masses high Sun season
  • Continental Tropical air masses low Sun season.

This climate has distinct wet/dry periods. The seasonal pattern of moisture is due to the migration of the intertropical convergence zone.

• The wet season is synchronous with the high Sun and the presence of the convergence zone.
• The dry season is a result of the more stable air developing from the subsidence associated with the presence of the subtropical high zone during the low Sun season.
• During the rainy season, the climate of this location is similar to the tropical wet climate: warm, humid, and has frequent thunderstorms.
• During the dry season more or less semi-desert conditions prevail. Some regions may experience intensification of rainfall because of monsoon development and orographic uplift.

Aw – Darwin, Australia 12.5° S , Elevation: 27 m

Am – Mangalore, India 13° N , Elevation: 22 m

Subtropical Desert and Steppe
Köppen Classification – BWh and BSh.

Dominated by Continental Tropical air masses all year.

This climate type covers 12 percent of all land area on the continents. The heart of the tropical desert climate is found near the tropics of Cancer and Capricorn, usually toward the western side of the continents. Regions with this climate have the following common climatic characteristics:

• low relative humidity and cloud cover.
• low frequency and amount of precipitation.
• high mean annual temperature.
• high monthly temperatures.
• high diurnal temperature ranges.
• high wind velocities.

The tropical desert climate is influenced by upper air stability and subsidence which is the result of the presence of the subtropical high pressure zone. Relative humidity is normally low, averaging 10 to 30 percent in interior locations. Precipitation is very low in quantity and very infrequent in distribution, both temporally and spatially.

Temperature varies greatly both diurnally and annually. The highest average monthly temperatures on the Earth are found in the tropical desert. They range between 29 to 35° Celsius. Winter monthly temperatures can be 15 to 25° cooler than summer temperatures. This climate also has extreme diurnal ranges of temperature. The average diurnal range is from 14 to 25° Celsius.

BWh – Alice Springs, Australia 23.5° S , Elevation: 579 m

BSh – Monterrey, Mexico 26° N , Elevation: 512 m

Mid-Latitude Desert and Steppe
Köppen Classification – BWk and BSk.

Dominated by Continental Tropical air masses during summer and Continental Polar in winter.

This climate type covers 14 percent of all land area on the continents. Regions with this climate have the following similar climatic characteristics:

• • low relative humidity and cloud cover.
  • low frequency and amount of precipitation.
  • moderate to high annual temperature.
  • moderate to high monthly temperatures.

These climates are dry because of extreme continentality and the effect of high elevations. Being located at the center of a continent limits the amount of moisture supplied from ocean sources. Without this moisture precipitation can not occur. The presence of mountains upwind of these climates can further reduce moisture availability because of the rainshadow effect. Major expanses of mid-latitude deserts can be found east of the Caspian Sea, north of the Himalayas, in western United States, and east of the Andes in a narrow region in southern South America. Mid-latitude deserts have a greater range of both daily and annual temperatures than their subtropical counterparts. In most cases, summer temperatures are not as high in mid-latitude deserts when compared to subtropical deserts. There are, however, exceptions like Death Valley, California which is one of the hottest places on our planet. Winter temperatures tend to be quite cool.

Mid-latitude steppe climates cover considerable parts of western North America and central Asia. This climate generally has similar temperature characteristics as mid-latitude deserts. However, mid-latitude steppe climates do receive slightly more precipitation than mid-latitude deserts.

BWk – Lovelock, Nevada, USA 40° N , Elevation: 1211 m

BSk – Williston, North Dakota, USA 47.5° N , Elevation: 579 m

Mid-Latitude Wet
Köppen Classification – Cf and Df.

Maritime Tropical in summer and Maritime Polar in winter.

The Mid-Latitude Wet climate is found in the Northern Hemisphere in the region from 60° North to 25 to 30° North mainly along the eastern margins of the continents. In North America, this climate extends from the Pacific coast of Canada at latitudes above 55° eastward to the Atlantic coast where it dominates the eastern half of the continent. In the Southern Hemisphere, this climate exists on the Southeastern tip of South America, New Zealand and the Southeast coast of Australia.

Summer weather is dominated by Maritime Tropical air masses which produce many thunderstorms from daytime heating. Monthly average temperature ranges from 21 to 26° Celsius with the tropical areas going as high as 29° Celsius. This is slightly warmer than the humid tropics. Frontal weather associated with the mid-latitude cyclone dominates the climate of more polar areas and is more frequent in all regions in the winter.

Precipitation in this climate is fairly evenly distributed throughout the year. Annual totals of precipitation are quite variable and depend on the latitude and continental position of the regions. During the summer and on the equatorial margins, convectional rainfall is the primary mechanism of precipitation. The southeast of the United Sates averages 40 to 60 days of thunderstorms per year. The frequency of thunderstorms decreases rapidly from south to north. Hurricanes also provide a mechanism for producing precipitation in more tropical regions of this climate.

Cf – London, England 51.5° N , Elevation: 5 m

Df – Winnipeg, Canada 50° N , Elevation: 240 m

Mid-Latitude Winter-Dry
Köppen Classification – Cw and Dw.

Maritime Tropical air masses in summer and Continental Polar air masses in winter.

This climate is characterized by a strong seasonal pattern of both temperature and precipitation. The normal location of the Mid-Latitude Winter-Dry climate is in the interior of the continents in the mid-latitudes. This continental location causes a large annual temperature range because of continentality.

This climate receives Maritime Tropical air masses in the summer with occasional Continental Tropical air masses from the adjacent deserts. Summers are hot and humid with intense summer convectional storms. Continental Polar air masses are dominant in the winter with an occasional outbreak of Maritime Polar air. Continental Polar air masses are associated with cold, dry weather conditions. Precipitation mainly occurs in the summer from thunderstorm activity. The mid-latitude cyclone produces a smaller quantity of precipitation in the winter.

Cw – Omaha, Nebraska, USA 41° N , Elevation: 298 m

Dw – Calgary, Canada 51° N , Elevation: 1140 m

Mid-Latitude Summer-Dry

•Köppen Classification – Cs.

•Summer weather is dominated by Continental Tropical air, while in the winter, Maritime Polar air masses are frequent.

The Mid-Latitude Summer-Dry climate is found on the western margins of the continents between 30 to 40° of latitude. Usually, this climate does not spread into the continents very far. This climate is often called a Mediterranean climate.

Precipitation falls mainly in the winter in this climate via the mid-latitude cyclone. During the summer these areas are influenced by stable subtropical highs, that give them dry, warm weather.

Cs – Rome, Italy 42° N , Elevation: 131 m

Polar Tundra
Köppen Classification – ET.

•Maritime Polar in summer and Continental Polar or Arctic in winter.

The polar tundra climate is characterized by cold winters, cool summers, and a summer rainfall regime. Areas experiencing this climate are the North American Arctic coast, Iceland, coastal Greenland, the Arctic coast of Europe and Asia, and the Southern Hemisphere islands of McQuarie, Kerguelen, and South Georgia. Annual precipitation averages less than 250 mm for most locations and most of this precipitation falls during the summer.

ET – Barrow, Alaska, USA 72° N , Elevation: 9 m

Polar Ice Cap
Köppen Classification – EF.

•Continental Arctic and Continental Polar air masses dominate.

Polar ice cap climates are located in the high latitudes over continental areas, like Greenland and the Antarctica. This climate type covers a vast area of the planet. For half of the year no solar radiation is received. During the summer months, available insolation is fairly high because of long days and a relatively transparent atmosphere. However, the albedo of snow-covered surfaces reflects up 90 percent of the insolation back to space. Average monthly temperatures are all generally below zero° Celsius. Winds are consistent and velocity is high enough to produce blizzard conditions most of the time.

Mean monthly temperature and precipitation values for Eismitte,

Greenland.

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Climate Change

• Introduction
• Evidences
• Causes
• Effects
• International Efforts

The climate system is comprised of five interacting parts, the atmosphere (air), hydrosphere (water), cryosphere (ice and permafrost), biosphere (living things), and lithosphere (earth’s crust and upper mantle). The climate system receives nearly all of its energy from the sun, with a relatively tiny amount from earth’s interior. The climate system also gives off energy to outer space. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth’s energy budget. When the incoming energy is greater than the outgoing energy, earth’s energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.

Evidences 

Evidence for climatic change is taken from a variety of sources that can be used to reconstruct past climates. Reasonably complete global records of surface temperature are available beginning from the mid-late 19th century. For earlier periods, most of the evidence is indirect—climatic changes are inferred from changes in proxies, indicators that reflect climate, such as vegetation, ice cores,dendrochronology, sea level change, and glacial geology.

Temperature (surface and oceans)

The instrumental temperature record from surface stations was supplemented by radiosonde balloons, extensive atmospheric monitoring by the mid-20th century, and, from the 1970s on, with global satellite data as well. Taking the record as a whole, most of the 20th century had been unprecedentedly warm, while the 19th and 17th centuries were quite cool.

Warming oceans

The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of ocean showing warming of more than 0.4 degrees Fahrenheit since 1969.

Shrinking ice sheets

The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA’s Gravity Recovery and Climate Experiment show Greenland lost an average of 286 billion tons of ice per year between 1993 and 2016, while Antarctica lost about 127 billion tons of ice per year during the same time period. The rate of Antarctica ice mass loss has tripled in the last decade.

Glacial retreat

Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.

Decreased snow cover

Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and that the snow is melting earlier.

Sea level rise

Global sea level rose about 8 inches in the last century. The rate in the last two decades, however, is nearly double that of the last century and is accelerating slightly every year.

Declining Arctic sea ice

Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades.

Extreme events

The number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing, since 1950. The U.S. has also witnessed increasing numbers of intense rainfall events

Ocean acidification

Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent. This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tons per year.

Most climate scientists agree the main cause of the current global warming trend is human expansion of the “greenhouse effect” — warming that results when the atmosphere traps heat radiating from Earth toward space.

Certain gases in the atmosphere block heat from escaping. Long-lived gases that remain semi-permanently in the atmosphere and do not respond physically or chemically to changes in temperature are described as “forcing” climate change. Gases, such as water vapor, which respond physically or chemically to changes in temperature are seen as “feedbacks.”

Causes 

Human expansion of the “greenhouse effect”

Gases that contribute to the greenhouse effect include:

• Water vapor. The most abundant greenhouse gas, but importantly, it acts as a feedback to the climate. Water vapor increases as the Earth’s atmosphere warms, but so does the possibility of clouds and precipitation, making these some of the most important feedback mechanisms to the greenhouse effect.
• Carbon dioxide (CO2). A minor but very important component of the atmosphere, carbon dioxide is released through natural processes such as respiration and volcano eruptions and through human activities such as deforestation, land use changes, and burning fossil fuels. Humans have increased atmospheric CO2 concentration by more than a third since the Industrial Revolution began. This is the most important long-lived “forcing” of climate change.
• Methane. A hydrocarbon gas produced both through natural sources and human activities, including the decomposition of wastes in landfills, agriculture, and especially rice cultivation, as well as ruminant digestion and manure management associated with domestic livestock. On a molecule-for-molecule basis, methane is a far more active greenhouse gas than carbon dioxide, but also one which is much less abundant in the atmosphere.
• Nitrous oxide. A powerful greenhouse gas produced by soil cultivation practices, especially the use of commercial and organic fertilizers, fossil fuel combustion, nitric acid production, and biomass burning.
• Chlorofluorocarbons (CFCs). Synthetic compounds entirely of industrial origin used in a number of applications, but now largely regulated in production and release to the atmosphere by international agreement for their ability to contribute to destruction of the ozone layer. They are also greenhouse gases.

On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO2). This happens because the coal or oil burning process combines carbon with oxygen in the air to make CO2. To a lesser extent, the clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases.

The consequences of changing the natural atmospheric greenhouse are difficult to predict, but certain effects seem likely:

• On average, Earth will become warmer. Some regions may welcome warmer temperatures, but others may not.
• Warmer conditions will probably lead to more evaporation and precipitation overall, but individual regions will vary, some becoming wetter and others dryer.
• A stronger greenhouse effect will warm the oceans and partially melt glaciers and other ice, increasing sea level. Ocean water also will expand if it warms, contributing further to sea level rise.
• Meanwhile, some crops and other plants may respond favorably to increased atmospheric CO2, growing more vigorously and using water more efficiently. At the same time, higher temperatures and shifting climate patterns may change the areas where crops grow best and affect the makeup of natural plant communities.

Solar irradiance

It’s reasonable to assume that changes in the Sun’s energy output would cause the climate to change, since the Sun is the fundamental source of energy that drives our climate system.

Indeed, studies show that solar variability has played a role in past climate changes. For example, a decrease in solar activity is thought to have triggered the Little Ice Age between approximately 1650 and 1850, when Greenland was largely cut off by ice from 1410 to the 1720s and glaciers advanced in the Alps.

But several lines of evidence show that current global warming cannot be explained by changes in energy from the Sun:

• Since 1750, the average amount of energy coming from the Sun either remained constant or increased slightly.
• If the warming were caused by a more active Sun, then scientists would expect to see warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere, and a warming at the surface and in the lower parts of the atmosphere. That’s because greenhouse gases are trapping heat in the lower atmosphere.
• Climate models that include solar irradiance changes can’t reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases.

Effects

Global climate change has already had observable effects on the environment. Glaciers have shrunk, ice on rivers and lakes is breaking up earlier, plant and animal ranges have shifted and trees are flowering sooner.

Effects that scientists had predicted in the past would result from global climate change are now occurring: loss of sea ice, accelerated sea level rise and longer, more intense heat waves.

Scientists have high confidence that global temperatures will continue to rise for decades to come, largely due to greenhouse gases produced by human activities. The Intergovernmental Panel on Climate Change (IPCC), which includes more than 1,300 scientists from the United States and other countries, forecasts a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century.

According to the IPCC, the extent of climate change effects on individual regions will vary over time and with the ability of different societal and environmental systems to mitigate or adapt to change.

The IPCC predicts that increases in global mean temperature of less than 1.8 to 5.4 degrees Fahrenheit (1 to 3 degrees Celsius) above 1990 levels will produce beneficial impacts in some regions and harmful ones in others. Net annual costs will increase over time as global temperatures increase.

“Taken as a whole,” the IPCC states, “the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time.”

International Efforts to Counter Climate Change

The Intergovernmental Panel on Climate Change (IPCC)

Created in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), the objective of the IPCC is to provide governments at all levels with scientific information that they can use to develop climate policies. IPCC reports are also a key input into international climate change negotiations.

The IPCC is an organization of governments that are members of the United Nations or WMO. The IPCC currently has 195 members. Thousands of people from all over the world contribute to the work of the IPCC. For the assessment reports, IPCC scientists volunteer their time to assess the thousands of scientific papers published each year to provide a comprehensive summary of what is known about the drivers of climate change, its impacts and future risks, and how adaptation and mitigation can reduce those risks.

The IPCC has published five comprehensive assessment reports reviewing the latest climate science, as well as a number of special reports on particular topics. These reports are prepared by teams of relevant researchers selected by the Bureau from government nominations. Expert reviewers from a wide range of governments, IPCC observer organizations and other organizations are invited at different stages to comment on various aspects of the drafts.

The IPCC published its First Assessment Report (FAR) in 1990, a supplementary report in 1992, a Second Assessment Report (SAR) in 1995, a Third Assessment Report (TAR) in 2001, a Fourth Assessment Report (AR4) in 2007 and a Fifth Assessment Report (AR5) in 2014. The IPCC is currently preparing the Sixth Assessment Report (AR6), which will be completed in 2022.

In December 2007, the IPCC was awarded the Nobel Peace Prize “for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change”. The award is shared with Former U.S. Vice-President Al Gore for his work on climate change and the documentary An Inconvenient Truth.

United Nations Framework Convention on Climate Change (UNFCCC)

The United Nations Framework Convention on Climate Change (UNFCCC) is an international environmental treaty adopted on 9 May 1992 and opened for signature at the Earth Summit in Rio de Janeiro from 3 to 14 June 1992. It then entered into force on 21 March 1994, after a sufficient number of countries had ratified it. The UNFCCC objective is to “stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”. The framework sets non binding limits on greenhouse gas emissions for individual countries and contains no enforcement mechanisms. Instead, the framework outlines how specific international treaties (called “protocols” or “Agreements”) may be negotiated to specify further action towards the objective of the UNFCCC

Kyoto Protocol

The Kyoto Protocol is an international treaty which extends the 1992 United Nations Framework Convention on Climate Change (UNFCCC) that commits state parties to reduce greenhouse gas emissions, based on the scientific consensus that (part one) global warming is occurring and (part two) it is extremely likely that human-made CO2 emissions have predominantly caused it. The Kyoto Protocol was adopted in Kyoto, Japan on 11 December 1997 and entered into force on 16 February 2005. There are currently 192 parties (Canada withdrew from the protocol, effective December 2012) to the Protocol.

The Protocol is based on the principle of common but differentiated responsibilities: it acknowledges that individual countries have different capabilities in combating climate change, owing to economic development, and therefore puts the obligation to reduce current emissions on developed countries on the basis that they are historically responsible for the current levels of greenhouse gases in the atmosphere.

Parties to the Kyoto protocol are classified as:

Annex I: Parties to the UNFCCC listed in Annex I of the Convention. These are the industrialized

(developed) countries and “economies in transition” (EITs). EITs are the former centrally-planned

(Soviet) economies of Russia and Eastern Europe. The European Union-15 (EU-15) is also an Annex I

Party.

Annex II: Parties to the UNFCCC listed in Annex II of the Convention. Annex II Parties are made up of

members of the Organization for Economic Cooperation and Development (OECD). Annex II Parties

are required to provide financial and technical support to the EITs and developing countries to assist

them in reducing their greenhouse gas emissions (climate change mitigation) and manage the

impacts of climate change (climate change adaptation).

Annex B: Parties listed in Annex B of the Kyoto Protocol are Annex I Parties with first or second

round Kyoto greenhouse gas emissions targets.

Non-Annex I: Parties to the UNFCCC not listed in Annex I of the Convention are mostly low-income

developing countries. Developing countries may volunteer to become Annex I countries when they

are sufficiently developed.

Least-developed countries (LDCs): 49 Parties are LDCs, and are given special status under the treaty

in view of their limited capacity to adapt to the effects of climate change.

• Industrialized countries (Annex I) have to report regularly on their climate change policies and measures, including issues governed by the Kyoto Protocol (for countries which have ratified it). They must also submit an annual inventory of their greenhouse gas emissions, including data for their base year (1990) and all the years since.
• Developing countries (Non-Annex I Parties) report in more general terms on their actions both to address climate change and to adapt to its impacts – but less regularly than Annex I Parties do, and their reporting is contingent on their getting funding for the preparation of the reports, particularly in the case of the Least Developed Countries.
• Kyoto Mechanisms are also known as Flexible Mechanisms and they include Emissions Trading, the Clean Development Mechanism and Joint Implementation to lower the cost of achieving emission targets.
• Emission Trading: Emissions Trading‐mechanism allows parties to the Kyoto Protocol to buy ‘Kyoto units’ (emission permits for greenhouse gas) from other countries to help meet their domestic emission reduction targets.
• Joint Implementation: Any Annex I country can invest in emission reduction projects (referred to as “Joint Implementation Projects”) in any other Annex I country as an alternative to reducing emissions domestically.
• Clean Development Mechanism (CDM): Countries can meet their domestic emission reduction targets by buying greenhouse gas reduction units from (projects in) non Annex I countries to the Kyoto protocol.
• Kyoto Units: The emissions trading can be international or domestic. Under the International Emissions Trading (IET), the countries can trade in the international carbon credit market to cover their shortfall in Assigned amount units. Countries with surplus units can sell them to countries that are exceeding their emission targets under Annex B of the Kyoto Protocol.
• Certified Emission Reductions (CERs): Certified Emission Reductions are one of the types of the Kyoto Units. They are issued under the Clean Development Mechanism. The Annex‐I countries can use the CERs to comply with their emission limitation targets or by operators of installations covered by the European Union Emission Trading Scheme (EU ETS) in order to comply with their obligations to surrender EU Allowances, CERs or Emission Reduction Units (ERUs) for the CO2 emissions of their installations. The Government and Private entities can hold the CERs on electronic accounts with the UN.

In Doha, Qatar, on 8 December 2012, the “Doha Amendment to the Kyoto Protocol” was adopted. The amendment includes:

New commitments for Annex I Parties to the Kyoto Protocol who agreed to take on commitments in a second commitment period from 1 January 2013 to 31 December 2020;

A revised list of greenhouse gases (GHG) to be reported on by Parties in the second commitment period; and

Amendments to several articles of the Kyoto Protocol which specifically referenced issues pertaining to the first commitment period and which needed to be updated for the second commitment period.

The Kyoto Protocol is seen as an important first step towards a truly global emission reduction regime that will stabilize GHG emissions, and can provide the architecture for the future international agreement on climate change.

In Durban (2011), the Ad Hoc Working Group on the Durban Platform for Enhanced Action (ADP) was established to develop a protocol, another legal instrument or an agreed outcome with legal force under the Convention, applicable to all Parties. The ADP is to complete its work as early as possible, but no later than 2015, in order to adopt this protocol, legal instrument or agreed outcome with legal force at the twenty-first session of the Conference of the Parties and for it to come into effect and be implemented from 2020.

The Paris Agreement (French: Accord de Paris)[3] is an agreement within the United Nations Framework Convention on Climate Change (UNFCCC), dealing with greenhouse-gas-emissions mitigation, adaptation, and finance, starting in the year 2020. The agreement’s language was negotiated by representatives of 196 state parties at the 21st Conference of the Parties of the UNFCCC in Le Bourget, near Paris, France, and adopted by consensus on 12 December 2015.[4][5] As of March 2019, 195 UNFCCC members have signed the agreement, and 185 have become party to it. The Paris Agreement’s long-term goal is to keep the increase in global average temperature to well below 2 °C above pre-industrial levels; and to limit the increase to 1.5 °C, since this would substantially reduce the risks and effects of climate change.

Under the Paris Agreement, each country must determine, plan, and regularly report on the contribution that it undertakes to mitigate global warming.[6] No mechanism forces a country to set a specific target by a specific date, but each target should go beyond previously set targets. In June 2017, U.S. President Donald Trump announced his intention to withdraw his country from the agreement. Under the agreement, the earliest effective date of withdrawal for the U.S. is November 2020, shortly before the end of President Trump’s current term. In practice, changes in United States policy that are contrary to the Paris Agreement have already been put in place.

The Paris Agreement

India is the world’s fourth largest economy and fifth largest greenhouse gas emitter. India accounts for about 5% of global emissions.

India’s emissions surged 65% between 1990 and 2005 and are projected to increase another 70% by 2020.

When compared to other major economies, India’s emissions are low. India accounts for only 2% of cumulative energy-related emissions since 1850.

On a per capita basis, India’s emissions are 70% below the world average and 93% below those of the United States.

India’s importance

The importance of New Delhi’s support to the climate pact is seen in the fact that India accounts for over 4% of global emissions and is important for crossing the threshold mark of 55%.

The world’s top two polluters are the US and China. They both together account for 40% of global carbon emissions, have already ratified the document.

Once the 55% barrier is crossed, the climate regime will become legally binding on all signatories after a period of 30 days.

India’s Policies on Climate Change:

India has introduced a number of policies that work towards climate change control by reducing or avoiding greenhouse gas emissions.

In June 2008, Indian government released India’s first National Action Plan on Climate Change, which identified eight core “national missions” running through 2017.

The National Action Plan is mentioned in India’s current Five-Year Plan (2012-2017), which guides overall economic policy. The goals pertaining to climate change are included in this plan which are-

• Reduce emissions intensity in line with India’s Copenhagen pledge; and

• Add 300,000 MW of renewable energy capacity.

Since taking office in May 2014, the present government has taken steps to scale up clean energy production and has initiated a shift in India’s stance in international climate negotiations.

One of the government’s first acts was to rename the environment ministry the Ministry of Environment, Forests and Climate Change.

In January, the newly reconstituted Prime Minister’s Council on Climate Change launched new initiatives on coastal zone management, wind energy, health and waste-to-energy.

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