Distribution of Temperature on the Earth’s Surface | Earth | Geography

The following factors control the distribution of temperature on the earth’s surface: 1. Latitudes 2. Altitude 3. Distance from the Coast 4. Nature of Land and Water 5. Nature of Ground Surface 6. Nature of Ground Slope 7. Prevailing Winds 8. Ocean Currents.

Factor # 1. Latitudes:

The temperature of the atmosphere of a particu­lar place near the ground surface depends on the amount of insolation received at that place. Since the amount of insolation received by the ground surface decreases poleward from the equator i.e., from low latitudes towards high latitudes because the sun’s rays become more and more oblique (slanting) poleward and hence air temperature also decreases poleward.

It may be noted that though sun’s rays are almost vertical over the equator throughout the year but there is no maximum temperature on it rather maximum tempera­ture is recorded along 20°N latitude in July because major portion of insolation is reflected by clouds and sizeable amount of heat is lost in evaporation in the low latitude zone (equatorial zone).

Factor # 2. Altitude:

The temperature decreases with increasing height from the earth’s surface at an average rate of 6.5°C per kilometre because of the following reasons:

(i) The major source of atmospheric heat is the earth’s surface from where heat is transferred to the atmosphere through the processes of conduction, radiation and convection. Thus, the portion of the atmosphere coming in direct contact with the earth’s surface gets more heat from the ground surface than the portion lying above because as we ascend higher in the atmosphere the amount of heat to be transported above decreases and hence tempera­ture decreases aloft.

(ii) The layers of air are denser near the earth’s surface and become lighter with in­creasing altitudes. The lower layer of air contains more water vapour and dust particles than the layers above and hence it absorbs larger amount of heat radiated from the earth’s surface than the upper air layers.

Factor # 3. Distance from the Coast:

The marine environment moderates the weather conditions of the coastal areas because there is more mixing of temperatures of the coastal seas and oceans and coastal lands due to daily rhythm of land and sea breezes. Thus, the daily range of temperature near the coastal environment is minimum but it increases as the distance from the sea coast increases. Minimum daily range of temperature is the characteristic feature of marine climate while extremely high daily range of temperature characterizes continental climate.

Factor # 4. Nature of Land and Water:

The contrasting nature of land and water sur­faces in relation to the incoming shortwave solar radia­tion largely affects the spatial and temporal distribu­tion of temperature. It may be pointed out that land becomes warm and cold more quickly than the water body. This is why even after receiving equal amount of insolation the temperature of land becomes more than the temperature of the water body.

The following reasons explain the differential rate of heating and cooling of land and water:

(i) The sun’s rays penetrate to a depth of only 3 feet in land because it is opaque but they penetrate to greater depth of several metres in water because it is transparent to solar radiation. The thin layer of soils and rocks of land, thus, gets heated quickly because of greater concentration of insolation in much smaller mass of material of ground surface. Similarly, the thin ground layer emits heat quickly and becomes colder.

On the other hand, the same amount of insolation falling on water surface has to heat larger volume of water because of the penetration of solar rays to greater depth and thus the temperature of ground surface becomes higher than that of the water surface though the amount of insolation received by both the surfaces may be equal.

(ii) The heat is concentrated at the place where insolation is received and there is very slow process of redistribution of heat by conduction because land sur­face is static. It may be noted that downward distribu­tion of temperature in the land surface within a day (24 hours) is effective upto the depth of only 10 centime­tres.

Thus, the land surface becomes warm during day and cold during night very rapidly. On the other hand, water is mobile. The upper surface of water becomes lighter when heated by insolation and thus moves away horizontally to other places and the solar rays have to heat fresh layer of cold water. Secondly, heat is redis­tributed in water bodies by sea waves, ocean currents and tidal waves. All these extend the period of warm­ing of water surface.

(iii) There is more evaporation from the seas and the oceans and hence more heat is spent in this process with the result oceans get less insolation than the land surface. On the other hand, there is less evaporation from the land surface because of very limited amount of water.

(iv) The specific heat (the amount of heat needed to raise the temperature of one gram of a substance by 1°C) of water is much greater than the land because the relative density of water is much lower than that of land surface. It means more heat is required to raise the temperature of one gram of water by 1°C than one gram of land.

More specifically, the heat required to raise the temperature of one cubic foot of water by 1°C is two times greater than the heat required for the equal volume of land (one cubic foot). It is apparent that same amount of insolation received by same mass of water and land would increase the temperature of land more than the temperature of equal mass of water.

(v) The reflection (albedo) of incoming solar radiation from the oceanic water surface is far more than from the land surface and thus water receives less insolation than land.

(vi) Oceanic areas are generally clouded and hence they receive less insolation than land surface. But clouds absorb outgoing terrestrial radiation and counter-radiate heat back to the earth’s surface. This process retards the loss of heat from the oceanic sur­faces and hence slows down the mechanism of cooling of the air lying over the oceans. On the other hand, land surfaces receive more insolation at faster rate because of less cloudiness and simultaneously lose more heat through outgoing terrestrial radiation very quickly.

Factor # 5. Nature of Ground Surface:

The nature of ground surface in terms of colour, vegetation, land use practices etc. affects the distribu­tion of temperature. The snow covered surfaces re­ceive very low amount of insolation because they reflect 70 to 90 per cent of incoming shortwave solar radiation and thus polar and arctic areas are characterized by extremely low temperature throughout the year.

On the other hand, sandy surfaces record high temperature during day time in the tropical and sub­tropical areas because they absorb most of solar radia­tion very quickly as they reflect only 20 to 30 per cent of solar radiation.

The following is the albedo of different kinds of surfaces:

Dark-coloured ground surfaces receive more solar radiation than light- coloured surfaces. The tem­perature of ground surface of forested areas never becomes very high because sizeable amount of heat is spent in the process of evapotranspiration from plant leaves.

Factor # 6. Nature of Ground Slope:

The ground slope facing the sun receives more insolation because the sun’s rays reach the surface more or less straight and hence sun-facing ground surfaces record higher temperature than the leeward slopes where sun’s rays reach more obliquely. In the northern hemisphere the southward facing slopes of east-west stretching mountains receive greater amount of insolation than the northward facing slopes because of their exposure to the sun for longer duration. This is why most of the valleys situated on the southern slopes of the Alpine mountains have settlements and cultiva­tion.

Factor # 7. Prevailing Winds:

The prevailing winds help in redistribution of temperature and in carrying moderating effects of the oceans to the adjacent coastal land areas. The winds blowing from low latitudes to high latitudes raise the temperature of the regions where they reach while winds blowing from high latitudes to low latitudes lower the temperature.

The winds blowing from oceans to coastal lands bring in marine effects and thus lower the daily range of temperature. The winds coming from higher parts of the mountains lower the temperature in the valleys. The temperature rises at the time of arrival of temperate cyclones while it falls sharply after their passage or their occlusion.

The winds associated with warm oceanic currents raise the temperature of coastal lands while the winds coming in contact with cold currents lower the temperature of affected coastal lands. For example, the North Atlantic Drift (extension of Gulf Stream) raises the temperature of coastal areas of north-western Europe and Labrador cold current lowers the temperature in the neighbourhood of New found-land.

Sometimes, local winds change the tem­perature dramatically. For example, the warm chinook winds raise the temperature by 30 to 40°F within a few minutes along the eastern slopes of the Rockies in the USA and the snow melts as by magic at the arrival of chinook.

This is why pastures are open throughout the year along the eastern slopes of the Rockies. Loo, a local hot wind, raises the temperature in the Ganga Plain of north India to such an extent (maximum temperature ranges between 40°C to 48°C during the day) that heat waves prolong for several days in con­tinuation and several people die of sun stroke.

Factor # 8. Ocean Currents:

The warm ocean currents flowing from tropical areas to temperate and cold zones raise the average temperature in the affected areas. For example, Gulf Stream raises the average temperature of the coastal areas of north-western Europe while Kuroshio warm current raises the temperature of Japanese coasts. Lab­rador, Peru, California, Kurile etc. cold currents lower the temperatures of affected areas. In fact, ocean cur­rents moving from one place to another equalize the temperatures.