It is in fact the varying amount of insolation received at the earth’s surface that brings about the differential heating of the earth. Temperature differences thus produced account for the density differences that drive the atmosphere in three- dimensional motion on global scale.
The weather scientists are of the opinion that much of the required energy to maintain the global circulation comes from the oceans in the tropical regions where there is a continuous transfer of large amounts of latent heat to the atmosphere through the process of evaporation.
The general circulation of atmosphere depends on many factors some of which are external to the earth. For example, the distribution pattern of temperature, pressure, and the resultant winds depends basically on the distribution of insolation and the orbit of our planet around the sun.
Besides, the geography of earth and the constituents of atmosphere also determine the general circulation pattern. Thus, the effects of changes in both internal and external factors on the general circulation of atmosphere are far-reaching.
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Presently, meteorologists are seriously engaged in developing mathematical models of general circulation which may be used in the study of weather and climate.
It has already been pointed out in an earlier chapter on the distribution of insolation that the tropical regions receive a larger amount of insolation than the temperate regions or the colder regions in higher latitudes.
Thus, there is a latitudinal imbalance in the heat budget of the earth. Winds are the means by which atmosphere tries to balance out the uneven distribution of temperature over the earth’s surface.
In the absence of planetary wind system it would have been impossible to compensate for the unequal distribution in the atmosphere of incoming solar energy and the loss of earth radiation.
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Besides the advectional transport of heat energy over the earth’s surface, winds also carry water vapour from over the bodies of water to land surfaces. But for winds the equatorial regions would become progressively hotter and the polar areas progressively colder.