Question

Describe the four factors that affect the distribution of temperature

Answer 1

The amount of insolation reaching the earth’s surface and its effectiveness per unit area depends on the following factors:

1. The Angle of Incidence or the Inclination of the Sun’s Rays:


The angle of incidence or the angle which the sun’s rays make with the earth’s surface, determines the amount of solar radiation which a particular place on the earth will receive. A smaller angle means the same amount of radiation will have to serve a larger area on the earth and the intensity will be less concentrated. A larger angle means the sun’s rays will be nearly vertical over the place and the given amount will have to serve a smaller area. As a result, the radiation received will be more concentrated and the intensity will be greater. See Fig. 2.2 (i) and



(ii) For instance, at 45° latitude, the amount of radiation received is only 75% of what is received at the equator. At Arctic/Antarctic Circles and at Poles, this figure is 50% and 40% respectively.

2. Duration of Sunshine:

The amount of solar radiation received obviously depends on the length of time that the sun shines over a particular place. At the equator, where the duration of sunshine is 12 hours daily throughout the year, the amount of radiation received is more compared to the other places on the earth. At winter solstice (22 December), the southern hemisphere receives more sunshine as it is summer there, while at summer solstice (21 June), the northern hemisphere receives more sunshine as it is summer time there. [Fig. 2.2 (iii)].

3. Transparency of Atmosphere:

The amount of cloud cover and its thickness, dust and water vapour which determine the transparency of the atmosphere affect the reflection, absorption and transmission of solar radiation. If the wavelength (X) of the radiation is more than the radius of the obstructing particle (such as a gas), then scattering of radiation takes place. If the wavelength is less than the obstructing particle (such as a dust particle), then total reflection takes place. Absorption of solar radiation takes place if the obstructing particles happen to be water vapour, ozone molecules, carbon dioxide molecules or clouds. [Fig. 2.2 (iv)].



4. Land-Sea Differential:

The temperature of the air resting over a landmass differs markedly from that of the air resting over an expanse of water in the same latitude: (i) Reflection is more by land than by sea. Especially snow covered areas reflect upto 70%-90% of insolation, (ii) Average penetration of insolation, and therefore heat, is more in water—upto 20 metres, than in land—where it is upto 1 metre only. Therefore, land cools more rapidly, (iii) The specific heat of water is 2.5 times higher than landmass, therefore water takes longer to get heated up and to cool down, (iv) The currents, tides and drifts exist only in oceans which carry the heat to lower layers. This delays the process of heating and cooling. [Fig. 2.3 (i)].

5. Prevailing Winds:



The oceanic winds have the capacity to take the moderating influence of the sea to coastal areas—reflected in cool summers and mild winters. This effect is pronounced only on the windward side. The leeward side or the interiors do not get the moderating effect of the sea, and therefore experience extremes of temperature. [Fig. 2.3 (ii)].

6. 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. In many valleys, settlements and cultivation are, therefore, concentrated on southern slopes, whereas northern slopes remain forested. In our country, this phenomenon is well observed in the Himalayan region. [Fig. 2.3 (ii)].



7. Ocean Currents:

Ocean currents influence the temperature of adjacent land areas considerably. Warm currents raise the temperatures of the coastal areas, whereas cold currents lower them. For instance, in higher latitudes, the eastern coasts have much lower temperatures than the western coasts due to the influence of cold currents. Similarly, the North Atlantic Drift, an extension of the warm Gulf Stream, keeps winter temperatures in Great Britain and much of Western Europe warmer than one would expect for their latitudes. Because of the prevailing westerly winds, the moderating effects of the ocean currents are carried far in land. (Fig. 2.4).



The influence of the old currents is most pronounced in the tropics or during the summer months in the mid-latitudes. For instance, the cold Benguela Current off the western coast of southern Africa moderates the tropical heat.

Answer 2

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