Draw a simplified diagram to show the general circulation of the atmosphere over the globe. What are the possible reasons for the formation of subtropical high pressure over 30° N and S latitudes?

Fig. Simplified general circulation of the atmosphere

The possible reasons for the formation of subtropical high pressure over 30°N and S latitudes are as under.
i. The air at the Inter-Tropical Convergence Zone (ITCZ) rises because of convection caused by high insolation and a low pressure is created. To this low pressure, the winds from tropics-the easterlies, converge. The converged air rises upto the height of 14 km and moves towards the North and South Poles. This causes accumulation of air at about 30°N and S. Part of the accumulated air sinks to the ground and forms a subtropical high pressure.
ii. The cooling of air when it reaches 30°N and S latitudes is also another reason for the sinking down below near the land surface. The air flows towards the equator as the easterlies. The easterlies from the side of the equator converge in the ITCZ. In the middle latitude, the circulation is that of sinking cold air that comes from the poles and the rising warm air that blows from the sub-tropical high. Thus it forms the subtropical high pressure over 30°N and S latitudes.