The temperature difference between the equator and the poles generates the global general circulation which redistributes heat from low latitudes to high latitudes. The general circulation is made up of a number of large-scale circulation cells, which consist of rising and descending air. Such large-scale vertical movement of air generates pressure differences across the Earth, which assist the development of surface winds that transfer the heat. Latitudinal differences in pressure delineate a number of major pressure zones which correspond with zones of climate .
Low pressure develops when air rises.
A major zone of low pressure exists at or near the equator, where the strong sunlight heats the Earth's surface and air in contact with it, causing it to rise. The climate associated with this zone of low pressure and rising air is tropical , with considerable rainfall in the form of daily thunderstorms. The tropical climate zone shifts north of the equator in summer and south of it in winter as the region of most intense solar radiation fluctuates with the seasons . Descending air increases atmospheric pressure, and subtropical climate is associated with generally clear skies, low rainfall, and high daytime temperatures of over 40 C. Many of the world's hot deserts are found in this subtropical high-pressure belt. As for the tropical belt of climate the subtropical zone expands towards the higher latitudes during the summer months.