Q. 1 How does the energy received in upper layer of the atmosphere keep changing at different times of the year?

 Answer Key Points: -

1) The solar energy 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.

2) During its revolution around the sun, the Earth is farthest from the sun (152 million km) on 4th July. This position of the Earth is called aphelion.

3) On 3rd January, the Earth is the nearest to the sun (147 million km). This position is called perihelion.

4) Therefore, the annual insolation received by the Earth on 3rd January is 6.6% more than the amount received on 4th July.

5) But, the effect of this variation in the solar energy does not have great effect on daily weather changes on the surface of the Earth because this variation is marked by other factors like the distribution of land and sea, and the atmospheric circulation.

Q. 2 Explain the factors affecting insolation at the surface of Earth.

 Answer Key Points: - 

The factors affecting insolation at the surface of Earth are:-

1) The Rotation of Earth on its Axis: - The fact that the Earth on its axis makes an angle of 66.5° with the plane of its orbit round the sun has a greater influence on the amount of insolation received at different latitudes.


2) The Angle of inclination of the Sunrays: - Since the Earth is spherical in shape, the sun’s rays strike the surface at different angles at different places. This depends on the latitude of the place. Vertical sunrays have to heat less area than the inclined rays. If more area is covered the energy gets distributed and the net energy received per unit area decreases. Moreover the slant rays have to pass through greater depth of the atmosphere resulting in more absorption, scattering and diffusion.

3) The Transparency of the Atmosphere: - The atmosphere is largely transparent to the short wave solar radiation. The incoming solar radiation passes through the atmosphere before striking the Earth’s surface. Within the troposphere water vapour, ozone and other gases absorb much of the near infrared radiation.

4) Duration/ Length of the Day: - Duration of the day varies from place to place and season to season. It decides the amount of insolation received on the Earth’s surface. The longer duration of the day means to receive greater amount of insolation and shorter duration of the day means to receive less insolation.

5) The Configuration of Land: - The insolation received at the surface varies from about 320 Watt/m2 in the tropics to about 70 Watt/m2 in the poles. Maximum insolation is received over the subtropical deserts due to lack of cloudiness. Equator receives comparatively less insolation than the tropics.

Generally, at the same latitude the insolation is more over the continent than over the oceans.

Q. 3 Discuss the process through which Earth and the atmosphere system maintain heat balance. Or Explain the heating and the cooling mechanism of atmosphere. Or Describe different ways of heating and cooling of the atmosphere. 

 Answer Key Points: -

The sun is the ultimate source of atmospheric heat and energy. There are different ways of heating and cooling of the atmosphere. They are: -

1) Terrestrial Radiation: - When the Earth’s surface is heated up by the insolation (in the form of short waves), it becomes a radiating body and the Earth’s surface starts to radiate energy to the atmosphere in the form of long waves this process is known as terrestrial radiation. This energy heats up the atmosphere from bottom to top. The atmosphere is transparent to short waves and opaque to long waves. Thus, the atmosphere is indirectly heated by the terrestrial radiation as long-wave radiation is absorbed by the greenhouse gases.

2) Conduction (Transfer of Heat by Contact): - Conduction is the process of heat transfer from a warmer object to a cooler object when they come in contact with each other. The flow of heat energy continues till the temperature of both the objects become equal or the contact is broken. The conduction in the atmosphere occurs at the zone of contact between the atmosphere and the Earth’s surface. Conduction is important in heating the lower layers of the atmosphere.

3) Convection (Vertical Transfer of Heat): - Transfer of heat by the movement of a mass or substance from one place to another, generally in vertical direction, is called convection. The air of the lower layers of the atmosphere gets heated either by the Earth’s radiation or by conduction. The Heating causes expansion, upliftment and decrease in density of the air. The cooler air comes down to fill the vacuum, leading to convection.

4) Advection (Horizontal Transfer of Heat): - The transfer of heat through horizontal movement of air (wind) is called advection. Horizontal movement of the air is relatively more important than the vertical movement as winds carry the temperature of one place to another. In tropical regions particularly in northern India during the summer season, local winds called ‘Loo’ is the outcome of advection process.

Q. 4 Atmosphere gets heated up indirectly by terrestrial radiation and not directly by sunrays. Explain. 

 Answer Key Points: -

1) The long wave radiation released by Earth’s surface is absorbed by the atmospheric gases particularly by carbon dioxide and the other greenhouse gases. Thus, the atmosphere is indirectly heated by the Earth’s radiation called Terrestrial Radiation.

2) The atmosphere in turn radiates and transmits heat to the space. Finally, the amount of heat received from the sun is returned to space, that maintains constant temperature at the Earth’s surface and in the atmosphere.

Q. 5 Why is the day temperature maximum in May and why not after the summer solstice in India?

 Answer Key Points: -

1) The main cause behind temperature being highest in May is due to Summer Solstice. At that time sun shines on the Tropic of Cancer which passes through middle of India. This position of the sun results in gradual heating of land mass in the northern hemisphere.

2) But after that in the beginning of June month due to the effect of monsoons the rain starts over entire Indian landmass which brings a cooling effect and India leads to gradual fall in temperature.

3) Although increase in temperature continues in India till 21 June and we find highest temperature in first week of June in India.

Q. 6 How do sunrays while passing through atmosphere gets absorbed? Or

Explain about heat budget of the Earth.

 Answer Key Points: -

The Earth receives almost all of its energy from the sun. The Earth in turn radiates back to space the energy received from the sun. As a result, the Earth neither warms up nor does it get cooled over a period of time this is called the Heat Balance or Heat Budget of the Earth. The insolation received at the top of the atmosphere is 100% (units). While passing through the atmosphere some amount of energy is reflected, scattered and absorbed. Only the remaining part reaches the Earth surface.

1) Roughly 35 units are reflected back to space even before reaching the Earth’s surface. Of these, 27 units are reflected back from the top of the clouds and 2 units from the snow and ice-covered areas of the Earth and 6 units scattered by space.

2) The reflected amount of radiation is called the albedo of the Earth.

3) The remaining 65 units are absorbed, 14 units within the atmosphere and 51 units by the Earth’s surface.

4) Of these 51 units, 17 units are radiated to space directly and the remaining 34 units are absorbed by the atmosphere (6 units absorbed directly by the atmosphere, 9 units through convection and turbulence and 19 units through latent heat of condensation).

5) 48 units absorbed by the atmosphere (14 units from insolation +34 units from terrestrial radiation) are also radiated back into space.

Q. 7 Explain the factors controlling temperature distribution at any place on the Earth. Or

What are the factors that control temperature distribution on the surface of the Earth?

 Answer Key Points: -

Factors controlling temperature distribution are: -

1) The Latitude: - The temperature of a place depends on the insolation received. The angle of incidence of sun’s rays goes on decreasing from the equator towards the poles. This is why the temperature is higher near the tropical regions and decreases towards the poles.

2) The Altitude: - As one goes on higher elevations the air gets thinner and its capacity to absorb the temperature reduces. On an average, temperature decreases at the rate of 1° C for every 165 m this is called 'Normal Lapse Rate'.

3) Distance from the Sea: - As compared to land, the sea gets heated slowly and loses heat slowly. Land heats up and cools down quickly. So, the difference in the temperature over the sea is less as compared to land. The places near the sea have a moderate temperature.

4) Ocean Currents: - Warm currents make the coasts warmer, along which they flow and 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).

5) Air-mass: - The places which come under the influence of warm air- masses experience higher temperature and the place that comes under the influence of cold air-masses experience low temperature.

6) Relief Features: - Different land surfaces have different rate of heating e.g. snow-covered land areas and vegetation covered land does not get excessively heated because of a large amount of reflection of solar energy. Moreover vegetation cover prevents quick radiation from the Earth whereas the soil without vegetation radiates it more rapidly. E.g. the temperature variations in densely forested areas are lower than those in desert areas.

Q. 8 Explain the distribution of temperature in January. 

 Answer Key Points: -

In January, the sun shines vertically overhead near the tropic of Capricorn. Hence, it is summer in Southern Hemisphere and winter in the Northern Hemisphere.

Northern Hemisphere

1. In January landmasses are cooler than the oceans in the Northern Hemisphere so the isotherms move to North over the ocean and to the South over the continent. This can be seen on the North Atlantic Ocean.

2. The pressure of warm ocean currents, Gulf Stream and north Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north.

3. Over the land the temperature decreases sharply and the isotherms bend towards South in Europe.

Southern Hemisphere

1. Due to few landmasses the effect of the ocean can be seen 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.

2. A high temperature of about 30°C is found over the landmasses mainly in three regions of North-West Argentina, East and Central Africa, and Central Australia in Southern Hemisphere.

Q. 9 Why is the annual range of temperature high in the Siberian plains? 

 Answer Key Points: -

1) Siberian plains are very far off from sea. Uneven climate is found in areas located away from oceans and seas.

2) The mean monthly temperature for January is between -18° C to -48° C in the Siberian plains. In summers, it is up to 20°celcius. Therefore, the annual range of temperature is -68 (-48-20) which is extremely high.

3) The pressure of warm ocean currents, Gulf Stream and north Atlantic drift, make the northern Atlantic Ocean warmer and the isotherms bend towards the north.

4) Over the land, the temperature decreases sharply and the isotherms bend towards south in Europe.

Q. 10 Explain the distribution of temperature in July.

 Answer Key Points: -

1) During this period the sun shines vertically overhead near Tropic of Cancer it is the summer for northern hemisphere and winter for southern hemisphere.

2) In the northern hemisphere the isotherms bend towards equator while crossing the oceans and towards pole ‘while crossing the landmass. In the Southern Hemisphere isotherms bend towards equator while crossing the land and towards pole ‘while crossing the oceans.

3) The isotherms are most irregular and zigzag in Northern Hemisphere on the other hand the isotherms are more regular and straight in Southern Hemisphere.

4) The regions having high temperature include South Western USA, the Sahara, the Arabia, Iraq, Iran, Afghanistan, desert region of India and China. However the lowest temperature below 0° C is recorded over Northern Hemisphere in the central parts of Greenland.

Q. 11 What is inversion of temperature? When and in what regions does it take place? Or 

Explain about inversion of temperature.

 Answer Key Points: -

Increase in temperature with increase in height is called Inversion of temperature. At times, the situations are reversed and the normal lapse rate is inverted.

 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) Ground Inversion (Surface Temperature Inversion): - This is the most common type of temperature inversion and occurs even on relatively plain surfaces. A long winter night with clear skies and still air is ideal situation for inversion. The heat of the day is radiated off during the night, and by early morning hours, the Earth is cooler than the air.

2) Frontal Inversion (Advectional type of Temperature Inversion): - There are places where many types of airmasses meet. The colder air mass is heavy so it settles down, while the warmer air mass is light so rises over the colder air mass. This creates temperature inversion. This type of inversion is unstable and is destroyed as the weather changes.

3) Temperature Inversion in Valley (Air Drainage Type of Inversion): - This type of inversion occurs in a valley, where the dense, cold lower level air drains down a slope to settle down at the bottom of the valley. As a result the valley floor has a lower temperature than the upper layers, which are relatively warm.

4) Subsidence Inversion (Upper Surface Temperature Inversion): - This temperature inversion is called upper surface temperature inversion because it takes place in the upper parts of the atmosphere. Sometimes massive upper layers get down 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. Subsidence inversions are common over the northern continents in winter (dry atmosphere) and over the subtropical oceans; these regions generally have subsiding air because they are located under large high-pressure centers.

Q. 12 Give the economic implications of temperature inversion. 

 Answer Key Points: -

1) Sometimes, the temperature of the air at the valley bottom reaches below freezing point, whereas the air at higher altitude remains comparatively warm. As a result, the trees along the lower slopes are bitten by frost, whereas those at higher levels are free from it.

2) Due to inversion of temperature, air pollutants such as dust particles and smoke do not disperse in the valley bottoms. Because of these factors, houses and farms in inter-montane valleys are usually situated along the upper slopes, avoiding the cold and foggy valley bottoms.

3) Fog reduces visibility and negatively affects vegetation and human settlements.

4) It makes stable environmental conditions that reduce rainfall.

Q. 13 Give the main features of Isotherms.

 Answer Key Points: -

1) Isotherms run along the latitudes but they are not parallel to the latitudes.

2) They take sudden bands while crossing the land and water even on the same latitude due to differential in heating and cooling of land and water.

3) Narrow spacing between isotherms indicates rapid change in temperature (high thermal gradient).

4) Wide spacing between isotherms indicates small or slow change in temperatures (low thermal gradient).

5) Distance between isotherms shows the rate of change of temperature.

6) Isotherms also change their position according to season during summers they bend towards Equator and during winters they turn away from Equator.