The actual conditions regarding the flow pattern on the earth’s surface are quite different from what has been described above.

From a comparison of the general circulation pattern with that for the months of July and January it becomes clear that as regards the actual wind systems there are considerable departures from the idealized flow pattern of general circulation.

The unequal distribution of oceans and continents, the prominent relief features of the earth’s surface, and the seasonal changes brought about by the revolution of our planet around the sun are the major factors which modify the idealized circulation pattern.