9. Solar radiation, heat balance and temperature.

NCERT Questions:

1. Multiple choice questions.

(i) The sun is directly overhead at noon on 21st June at:

a) The equator

b) 23.5˚ South

c) 23.5˚ North

d) 66.5˚ North

Ans. c) 23.5˚ North

(ii)  In which one of the following cities is the day the longest?

a) Thiruvananthapuram

b) Chandigarh

c) Hyderabad

d) Nagpur

Ans. a) Thiruvananthapuram

(iii) The atmosphere is mainly heated by the:

a) Shortwave solar radiation

b) Reflected solar radiation

c) Long wave statistical radiation

d) Scattered solar radiation

Ans. c) Long wave terrestrial radiation

(iv) Make correct pairs from the following two columns.

Ans.

(v) The main reason that the Earth experience is highest temperature in the subtropics in the northern hemisphere rather than at the equator is.

a) Subtropical areas tend to have less cloud cover than Equatorial areas.

b) Subtropical areas have longer day hours in the summer than the Equatorial.

c) Subtropical areas have an enhanced greenhouse effect compared to Equatorial areas.

d) Subtropical areas are nearer to the oceanic areas than the Equatorial locations.

Ans. b) Subtropical areas have longer day hours in the summer than the Equatorial.

2. Answer the following questions in about 30 words

(i) How does the unequal distribution of heat over the planet Earth in space and time cause variations in weather and climate.

Ans.

a) Weather and climate gets affected by the unequal distribution of temperature on the earth.

b) The areas where there is high temperature wind blows from low temperature areas.

c) The wind move upward from Equatorial regions and blow towards the poles. Due to this, wind pressure on both the poles increases.

d) In winter, wind blows from land regions to oceanic regions. Therefore these winds are dry.

e) On the other hand, during summers, wind blow from ocean towards land. Therefore these winds are humid.

f) Unequal distribution of temperature is mainly cause of blowing of wind.

g) Rainfall and cyclone also arise due to unequal distribution of temperature.

In this way, unequal distribution of temperature affects climate and weather.

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

Ans. Factors controlling temperature distribution are:

The temperature of air at any place is influenced by:

a) The latitude of the place

b) The altitude of the place

c) Distance from the sea, the air mass circulation

d) The presence of warm and cold ocean currents

e) Local aspects

a) The latitude: The temperature of a place depends on the insolation received. The insolation varies according to the latitude, hence the temperature also varies.

b) The altitude: The temperature is indirectly heated by terrestrial radiation from below. Therefore, the places near the sea level record higher temperature than the place situated at higher elevations.

c) Distance from the sea: Another factor is the location of a place with respect to the sea. Compared to land the sea gets heated slowly and loses heat slowly. Land heats up and cools down quickly. Therefore the difference in the temperature over the sea is less compared to land. And the place near the sea has a moderate temperature.

d) Air mass and ocean currents: Air mass affects the temperature, 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.

(iii) In India, why is the day temperature maximum in May and why not after the summer solstice?

Ans. The main cause behind temperature being highest in May is due to sun rays coming closer to Tropic of Cancer, the rays will be vertical on 21^st  of June on Tropic of Cancer. Tropic of Cancer passes through middle of India. It is because rain starts on Malabar Coast almost early June. Due to this temperature does not increase in South India although increase in temperature continues in India till 21st June. Gradually the monsoon covers the whole of India and brings the temperature down.

(iv) Why is the annual range of temperature high in the Siberian Plains?

Ans.

a) Siberian plains are quite far off from sea.

b) Uneven climate is found in areas located away from ocean and seas.

c) The main monthly temperature for January is between -18˚ C to -48˚ C in the Siberian plains.

d) In summers it is up to 20˚ C.

e) Therefore, the annual range of temperature is of 68˚ C e. -48˚ to 20˚ C, which is extremely high.

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

g) The areas which are closer to equator have temperature up to 27˚ C and over the land the temperature decreases sharply and the isotherms bend towards south in Europe. It is much pronounced in the Siberian plains.

3. Answer the following questions in about 150 words:

(i) How do the latitude and the tilt in the axis of rotation of the Earth affect amount of radiation received at the Earth’s surface?

Ans.

a) Sun rays fall vertically on equator almost throughout the year.

b) From 23.5˚ N and 23.5˚ S the sun rays keeps fluctuating.

c) From 21st March the sun is in Northern Hemisphere and sun rays fall vertically on Tropic of Cancer on 21st June. It is summer in the Northern hemisphere.

d) From 23rd September to 22nd December, the Sun is in Southern Hemisphere. During this time, the sun rays fall vertically on Tropic of Capricorn.

e) On 21st March and 23rd September, sun rays fall vertically on equator.

f) As we move towards poles from Tropic of Cancer and Tropic of Capricorn, temperature keeps on decreasing.

g) Therefore, after 66½˚ North and South there is cold zone. Throughout the year, the temperature remains very low here, known as Frigid Zone.

It is because the sun rays fall tilted on it. In this way, the latitude and the tilt in the axis of the Earth affect the amount of radiation received at the Earth’s surface. Hence the poles have six months day and six months night.

(ii) Discuss the process through which the earth-atmosphere system maintains heat balance.

Ans.

a) The Earth, after heating by insolation, transmits the heat to the atmospheric layers near to the Earth in long waveform.

b) The air in contact with the land gets heated slowly and the upper layers in contact with the lower layers also get heated through conduction.

c) It takes place when two bodies of unequal temperature are in contact with one another. There is a flow of energy from the warmer to cooler body. The transfer of heat continues until both the bodies attained the same temperature or the contact is broken. Conduction is important in heating the lower layers of the atmosphere.

d) Convection: The air in contact with the earth rises vertically on heating in the form of currents and transmits the heat of the atmosphere. This vertical heating of atmosphere is known as convection.

e) Advection: The transfer of heat through horizontal movement of air is called advection. Horizontal movement of the air is relatively more important than the vertical movement.

f) In tropical regions, particularly in northern India during summer seasons, a local wind called Loo is the outcome of advection process.

(iii) Compare the global distribution of temperature in January over the northern and the southern hemisphere of the Earth.

Ans.

a) In January there is summer in southern hemisphere and winter in the northern hemisphere.

b) The main reason behind it is that sun rays are closer to the Tropic of Capricorn.

c) The mean January temperature along 60˚ N latitude is -20˚ C. Both at 80˚ north and 50˚ north latitudes. The mean monthly temperature for January is over 27˚ C.

d) In Equatorial oceans, temperature is over 24˚ C in the tropics, and 2˚ C – 0˚ C in the middle latitudes and -18˚ C to -48˚ C in the Eurasian continental interior.

e) In the northern hemisphere the land surface area is much larger than the southern hemisphere. Hence the effects of land mass and the ocean currents are well pronounced in January the isotherms deviate to the north over the ocean and the south over the continents.

f) 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 bend towards the north.

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

Question Bank:

Multiple choice questions:

1. The atmosphere is generally heated by?

a) Solar radiation

b) Long wave terrestrial radiation

c) Reflected solar radiation

d) Scattered solar radiation

Ans. b) Long wave terrestrial radiation

It is a process by which heat waves are sent out by the earth’s surface.  At first, the sun heats the surface of the earth. The heat of the earth’s surface is then radiated back to the lower atmosphere. The air in the lower layer of the atmosphere gets heated.

2. Isotherms are the lines joining the places of equal:

a) Temperature

b) Distance

c) Pressure

d) Height

Ans. a) Temperature

Isotherms are lines drawn on the map or chart joining points with the same temperature. Isotherms are commonly used in meteorology to show the distribution of temperature at the earth’s surface.

3. Advection means transfer of heat through:

a) Vertical movement of air

b) Horizontal movement of air

c) No movement of air

d) Warming of the air

Ans. b) Horizontal movement of air

Transfer of heat through horizontal movement of air is called advection. Horizontal movement of air is relatively more important than the vertical movement of air.

4. Convectional heating is:

a) Lateral heating

b) Vertical heating

c) Heating of the atmosphere by insolation

d) Variation in daily weather

Ans. b) Vertical heating

The air in contact with earth rises vertically on heating in the form of currents and further transmits the heat of the atmosphere. This process of vertical heating of the atmosphere is known as convection. The air in contact with the earth rises vertically on heating in form of currents.

5. The long wave radiation is radiated by:

a) Sun

b) Moon

c) Earth

d) Stars

Ans. c) Earth

The insolation received by the earth is in short waves form, and heats up its surface. The earth after heating itself becomes a radiating body and it radiates energy to the atmosphere in long waves form. Hence heat absorbed by earth during day time is radiated back into the atmosphere in the nights in form of long waves.

6. The process of vertical heating of atmosphere is called:

a) Conduction

b) Convection

c) Radiation

d) Insolation

Ans. b) Convection

Convection is the transfer of internal energy into or out of an object by the physical movement of a surrounding fluid that transfer the internal energy along with its mass. It is confined only to the troposphere.

7. The earth’s surface receives most of its energy in form of:

a) Long wavelength

b) Radiation

c) Insolation

d) Short wavelength

Ans. d) Short wavelength

The energy received by the earth is in short wavelength is called insolation.

8. The variability in the solar output received at the top of the atmosphere is because of:

a) Variation in the distance between earth and the sun

b) Variation in the distance between earth and the moon

c) Variation in the distance between moon and the sun

d) None of the above

Ans. a) Variation in the distance between earth and the sun

The sun rays fall obliquely at the top of the atmosphere and the earth receives a very small portion of the sun’s energy.

9. The earth radiates energy to the atmosphere in:

a) Long wavelength

b) Radiation insolation

c) Insolation

d) Short wavelength

Ans. Long wavelength

This energy is responsible to heat up the atmosphere from below.

10. Seasonal contrast is maximum in:

a) Low latitudes

b) Mid-latitudes

c) High latitudes

d) Subtropics

Ans. Mid-latitudes

In middle latitudes, most of diurnal (day and night) variation in daily weather is caused by advection alone.

11. The days are longer at:

a) Tiruvananthpuram

b) Hyderabad

c) Chandigarh

d) Nagpur

Ans. a) Tiruvananthpuram

Tiruvananthpuram is nearer to the equator as compared to other places. Therefore the days are longest at Tiruvananthpuram.

12. The envelope of air is called:

a) Atmosphere

b) Troposphere

c) Stratosphere

d) None

Ans. a) Atmosphere

The envelope of air that surrounds the earth is known as atmosphere. It is a mixture of different gases. Nitrogen and oxygen constitute the majority of atmosphere, with carbon-dioxide. This helps to sustain life.

13. The earth is farthest from sun on:

a) 4^th August

b) 4^th January

c) 4^th July

d) 4^th March

Ans. 4^th July

During its revolution around the sun, the earth is farthest from the sun (152 million Km on 4^th July). This position is called Aphelion.

14. The highest range of temperature occurs in the areas having:-

a) Continental location

b) Coastal location

c) Intercontinental location

d) All the above

Ans. a) Continental location

The highest range of temperature occurs in the areas having continental location, which means areas inside a continent and away from the sea.

15. In the month of July the isotherms generally:

a) Run parallel to the latitudes

b) Are not parallel to the latitudes

c) Are perpendicular to the latitudes

d) None

Ans. a) Run parallel to the latitudes

In July, the isotherms generally run parallel to the latitudes. The equatorial ocean record warmer temperature, more than 27˚ C. Over the land more than 30˚C is noticed in the subtropical continental regions. The isotherm of 20˚C, 10˚C and 0˚C runs parallel to 35˚S, 45˚S and 60˚S latitudes respectively. In July the isotherms generally run parallel to the latitude.

16. Insolation refers to:

a) Wind direction

b) Solar radiation

c) Precipitation

d) None

Ans. Solar radiation

Incoming solar radiation is known as insolation.

17. The variability in the solar output received at the top of the atmosphere is because of:

a) Variation in the distance between earth and the sun

b) More heat radiated from the earth

c) Excessive heating of the atmosphere

d) Thin layer of atmosphere

Ans. a) Variation in the distance between earth and the sun

The sun rays fall obliquely on the top of atmosphere and the earth receives a very small amount of sun’s energy. It is because of the ozone layer present in the lower stratosphere that absorbs most of the ultra violet rays of the sun.

18. Air drainage ____________.

a) Causes damage to the plants from frost

b) Protects plants from frost damages

c) Has no impact on the plants

d) None

Ans. Air drainage protects plants from frost damages

General term for gravity induces, down slope flow of relatively cold air.

19. Differences in pressure on the earth surface causes:

a) Winds

b) Precipitation

c) Hail

d) Seasons

Ans. a) Winds

Pressure difference causes movement of wind. Wind moves from high pressure to low pressure.

20. In mountains and hill regions, the inversion of temperature takes place due to:

a) High temperature

b) Low temperature

c) Air drainage

d) None

Ans. c) Air drainage

The cold air of the mountains move down slope to pile up deep in the valley bottom with, this is called air drainage.

21. Which of the following statement is not correct regarding the temperature control of the atmosphere at a given place?

a) Temperature generally decreases with altitude on the either side of the equator

b) Temperature rises to maximum during summers and to minimum during winters

c) During night, the water surface cools more rapidly than the land surface

d) The major temperature contrast on earth’s surface is between land and water masses

Ans. c) During night, the water surface cools more rapidly than the land surface

Water takes more time in cooling and heating.

22. Shimla is cooler than Amritsar, although they are on the same latitude. This is because:

a) Shimla is in further north

b) Shimla is at a greater height above sea level than Amritsar

c) Shimla is farther than equator

d) Their longitudes differ.

Ans. b) Shimla is at a greater height above sea level than Amritsar.

Shimla is cooler than Amritsar because it is at a higher elevation and comes under the influence of cold winds.

23. Seasonal contrast is maximum in:

a) Low latitudes

b) High latitudes

c) Mid-latitudes

d) Subtropics

Ans. c) Mid-latitudes

Seasonal contrast is maximum in mid-latitudes. In mid-latitudes, most of diurnal (day and night) variations, in daily weather, are caused by advection.

24. Inversion of temperature means:

a) Increase in temperature with height

b) Decrease in temperature with height

c) No change in temperature

d) Static temperature

Ans. a) Increase in temperature with height

Normally temperature decreases with height. This process is known as normal lapse rate but when this condition gets reversed it is called inversion in temperature.

25. Distance from the sun when it is nearest to the sun is:

a) 47 million Km

b) 147 million Km

c) 447 million Km

d) 947 million Km

Ans. b) 147 million Km

During the revolution around the sun, the earth is farthest from the sun (152 million Km on 4^th July). This position of the earth is called Aphelion. On the3^rd January, the earth is nearest to the sun (147 million Km). This position is called Perihelion.

26. For the distribution of temperature, which one is not a controlling factor?

a) Latitude

b) Altitude

c) Distance from sea

d) Heat budget of the earth

Ans. d) Heat budget of the earth

It is total gain minus total loss of heat received by the earth.

27. Total gain minus total loss of heat received by the earth is the:

a) Conduction

b) Convection

c) Albedo of the earth

d) Heat budget of the earth

Ans. d) Heat budget of the earth

Heat budget of the earth is total gain minus total loss of heat received by the earth. The earth as a whole does not accumulate or lose heat. It maintains its temperature. This can happen only if the amount of heat received in the form of insolation equals to the amount loss by the earth through terrestrial radiation.

28. Aphelion position refers to the:

a) Earth nearest to the sun

b) Earth farthest from the sun

c) Moon nearest to the earth

d) None

Ans. Earth farthest from the sun

When the earth is farthest from the sun on 4^th July every year, earth is approximately 152 million Km away from the sun. On the other hand 3^rd January the position is named as Perihelion. The earth is approximately 147 million Km away from the sun.

29. What is Albedo?

a) The percentage of visible light reflected by an object

b) The difference of temperature between two areas

c) The incoming solar radiation

d) None

Ans. a) The percentage of visible light reflected by an object

The percentage of visible light reflected by an object is known as ‘albedo’. The reflected amount of radiation is called albedo of the earth.

30. The highest range of temperature occurs in the areas having:

a) Continental location

b) Coastal location

c) Intercontinental location

d) Polar location

Ans. a) Continental location

Equator receives comparatively less insolation than the tropics because of the presence of clouds. Remember the insolation is amount of sun light received on the earth’s surface per unit area. Hence the clouds obstruct sun light. Generally, at the same latitude the insolation is more over the continents than over the oceans.

31. Conduction refers to______.

a) Heating of the atmosphere horizontally

b) Vertical heating of the atmosphere

c) Heating of the atmosphere coming in contact with land

d) Heating process

Ans. c) Heating of the atmosphere coming in contact with land

Conduction takes place when two bodies of unequal temperature come in contact with one another. There is a flow of energy from the warmer to the cooler body.

32. The sun is vertically overhead at _______ on 21^st June:

a) The equator

b) 23 ½ ˚ N

c) 23 ½ ˚ S

d) 66 ½ ˚ N

Ans. b) 23 ½ ˚ N

The sun is vertically overhead at noon on 21^st June 23 ½ ˚ N at the Tropic of Cancer.  It is summer in the northern hemisphere and winter in southern hemisphere.

33. Maximum insolation is received over:

a) Equator

b) Tropical areas

c) Subtropical areas

d) Poles

Ans. c) Subtropical areas

Subtropical deserts receive maximum amount of insolation cloudiness is least there.

34. Scattering in the atmosphere takes place due to the presence of:

a) Small suspended particles

b) Large suspended particles

c) Gases in the air

d) All the above

Ans. a) Small suspended particles

These particles are dust, ash etc.

35. Which of the following is not a factor causing variations in insolation?

a) Rotation of the earth

b) The angle of inclination of sun rays

c) The greenhouse effect

d) The length of day

Ans. c) The greenhouse effect

It refers to the absorption of outgoing terrestrial radiation.

36. Absorption of outgoing terrestrial radiation refers to the:

a) Rotation of the earth

b) Angle of inclination of the sun rays

c) Greenhouse effect

d) Length of the day

Ans. c) Greenhouse effect;

It refers to absorption of outgoing terrestrial radiation. Rest are the factors causing variations in insolation.

Short answer type questions:

1. What is an albedo?

Ans. The percentage of visible light reflected by an object is albedo.

2. What is insolation?

Ans. The incoming solar radiation is termed as insolation it is in the form of short wave.

3. What is isotherm?

Ans. These are imaginary lines joining places having equal temperature. The temperature distribution is generally shown on the map with the help of isotherms.

4. What is air drainage?

Ans. The cold air acts almost like water and moves down the slope to pile up deeply in pockets and valley bottom with warm air above. This is called air drainage. It protects plants from frost damage

5. How is temperature affected by clouds?

Ans. Clouds check the outgoing radiation but on clearing nights there is unchecked radiation which escapes rapidly through the atmosphere.

6. What is convection?

Ans. Air in contact with the earth rises vertically, on heating. In the form of currents and further transmits the heat of the atmosphere, this process of vertical heating, of the atmosphere is known as convection.

7. What is direct solar radiation?

Ans. Sunlight reaching the Earth’s surface unmodified by any atmospheric process is turned into direct solar radiation.

8. How do winds affect the temperature of a place?

Ans. Cold and warm winds affect the horizontal distribution of temperature. Warm winds increase the temperature whereas cold winds reduce it.

9. Define solar radiation.

Ans. Sun is the ultimate source of energy on the earth. The incoming solar radiation from the sun is called solar radiation all bodies radiate energy in the form of waves. The hotter the body is more the intensity of radiation. The electromagnetic radiation emitted from the sun consists of visible light, ultraviolet light, infrared, radio waves, X-rays and gamma rays.

10. What are equinoxes?

Ans. On March 21^st and September 23^rd the sun is overhead at noon over the equator. These days are called equinoxes it is called vernal equinox on March 21^st and autumnal equinox on September 23^rd. On these dates days and nights are of equal length.

11. Name the factors controlling temperature distribution?

Ans. Temperature of air at any place is influenced by:

a) The latitude of the place

b) The altitude of the place

c) Distance from the sea

d) The presence of warm and cold ocean current

e) Local aspects

12. What is terrestrial radiation?

Ans. The insolation received by the earth is in short wave forms and heats up its surface. The earth after being heated becomes radiating body and it radiates energy to the atmosphere in long wave form. This energy heats up the atmosphere from below this process is known as terrestrial radiation.

13. Define inversion of temperature?

Ans. When the temperature increases with the increasing height this phenomena is called the inversion of temperature, it takes place in calm cold and clear winter nights because the Earth’s surface cools more rapidly in such nights and the movement of air is not there..

14. Give the general characteristics off isotherms.

Ans. The general characteristics of isotherms are:

a) Isotherm run along the latitudes but are not parallels of the latitudes

b) They take sudden bends at land water edges

c) They are drawn at equal spaces which indicate the latitudinal thermal gradient.

15. What is inversion of temperature?

Ans.  Inversion of temperature is important because of the following reasons:

a) It is helpful in several climatic conditions

b) Dense fog collects at the valley front.

c) Stratus clouds are formed below the layer

d) Smog is found beneath the inversion layer

16. Define variation in the net heat budget at the Earth’s surface

Ans. There are variations in the amount of radiation received at the Earth’s surface. Some parts of the earth have surplus radiation balance while the others have deficit.  There is a surplus of net radiation balance between 40˚ North and South and the regions near the poles have deficit.

17. What is advection?

Ans. The transfer of heat through the horizontal movement of air is called advection. This movement is relatively more important than the vertical movement in middle latitudes mostly of diurnal (day and night) variation in daily weather is caused by the advection alone. In northern India during summer season, local winds called loo, occur due to the advection process.

18. How do ocean currents affect the temperature of a place?

Ans. Ocean currents have great influence on the horizontal distribution of temperature, the masses of air that travel with ocean currents are often of different temperature then the location they travel to. Ocean currents can significantly alter the average temperatures of an area. Ocean currents can increase or reduce the temperature. i.e.,  Gulf Stream is a warm ocean current in the North Atlantic flowing from the Gulf of Mexico, northeast along the US coast and from there to the British Isles. The Gulf of Mexico has higher air temperature than Britain as its closer to the equator. This means that the air coming from the Gulf of Mexico to Britain is also warm.

19. How does latitude affect the temperature of a place?

Ans. Temperature decreases from the equator to the poles. Because, the sun rays fall more obliquely as we go north or south of the equator. The oblique rays spread on a larger area than the perpendicular rays and also passes thicker layer of the atmosphere where their heat is absorbed by water- vapour dust particles and carbon dioxide.

20. Does latitude affect the amount of radiation received by the earth?

Ans.  The amount of insolation received by a place on the surface of the earth depends upon the angle of inclination of the place. The angle of inclination of the sun rays depends on the latitude of a place. The higher the latitude, the lesser the angle of the rays, resulting in slant rays the area covered by vertical rays is always less than the slant rays. If more area is covered, the energy gets distributed and the net energy received per unit area decreases.

21. What is the effect of the tilt in the axis of earth on insolation variation?

Ans. The duration of sun shine or the length of the day vary at all places except at the equator due to the tilt in the axis of the earth. The length of the day and longer duration of sunlight enables the place to receive more amount of insolation.

22. Write a short note on heat budget.

Ans. Average temperature of the earth remains rather constant, it has been possible because whatever the amount of heat earth receives from the sun in the form of short waves it radiates back the same amount of heat up to the atmosphere in the form of long waves.  This balance of heat is termed as the earth’s heat budget.

23. Explain how altitude affects temperature?

Ans. The atmosphere is indirectly heated by terrestrial radiation from below. The places near the sea level record higher temperature than the places situated at higher elevations. In other words the temperature generally decreases with increasing height. The rate of decrease of temperature with height is termed as normal lapse rate and that is 6.5˚C at 1000 metre.

24. How distance from the sea influences the temperature? Explain.

Ans. Compared to land, the sea gets heated slowly and loses the heat in a slow manner. Land heats up and cools down quickly. Therefore, the variation in temperature over the sea is less compared to the land. The places situated near the sea come under the moderating influence because of sea and land breezes, which moderate the temperature.

25. What do you understand by vertical distribution of temperature?

Ans. The study of upper layers of atmosphere with the help of balloons, kites, aeroplanes, radio sounds etc. reveals that the temperature of air goes on falling upward at the rate of 6.5˚C at every 1000 metre of height. This is called normal lapse rate the temperature decreases with height because of the

a) Conduction from earth surface: the atmosphere is heated mainly by the terrestrial radiation. The atmosphere layer immediately overlying the Earth’s surface receives the maximum heat it is therefore the warmest. But as we go higher, the temperature gradually decreases and air becomes cooler because the increasingly higher layers receive a lesser amount of heat.

b) Difference in absorption: the lower layers have more of water vapour, dust particles, dense air etc. than the upper layers, therefore lower layers absorb a lot of heat from the earth surface and directly transfer heat from the solar radiations passing through them than upper layers. That is why lower layers are warmer than the upper layers.

26. Why is temperature reduced to sea level before isothermal maps are drawn?

Ans. Isotherms are lines drawn on a map or chart joining points with the same temperature. The temperature is reduced to sea level before isothermal maps are drawn so that the difference in temperature due to altitude at any place will not vary. Isotherms are commonly used in meteorology to show the distribution of temperature at the earth’s surface or on a chart indicating constant level of temperature.