The seasonal variations in the general pattern of surface pressure. The sun’s direct rays change positions as they migrate between the Tropics of Cancer and Capricorn. Thus, following the apparent movement of sun the pressure belts move northward in July and southward in January.
These seasonal variations in the pressure pattern are, of course, thermally induced. In the tropical region seasonal variations in pressure are no doubt very small, because temperatures remain uniformly high throughout the year with little variation.
In high latitudes, on the contrary, the seasonal variations in pressure tend to be much larger because of an increasing contrast in the angle of incidence and the length of daylight.
The general pattern of seasonal pressure variation is changed to a great extent in the northern hemisphere where there is preponderance of landmasses over the oceanic areas accounting for about 40% of the total surface.