The global circulation of air is explained through the three-cell air circulation model, which describes the movement of atmospheric air in each hemisphere of the Earth. This model helps in understanding the distribution of temperature, pressure belts, wind systems, and climatic conditions across the globe. The circulation pattern develops because the Earth receives unequal heating from the Sun and rotates on its axis. The equatorial regions receive maximum solar energy, while the polar regions receive minimum heat. This unequal heating creates pressure differences that drive atmospheric circulation. The rotation of the Earth further modifies the direction of winds through the Coriolis force. The atmosphere in each hemisphere is divided into three major circulation cells known as the Hadley Cell, Ferrel Cell, and Polar Cell. The Hadley Cell operates between the Equator and about 30° latitude in both hemispheres. The Equator experiences intense heating because the Sun’s rays fall almost vertically throughout the year. The heated air becomes lighter and rises upward, creating a zone of low pressure called the Equatorial Low Pressure Belt or Intertropical Convergence Zone (ITCZ). As the warm air rises, it expands and cools, causing condensation and heavy rainfall. This process explains the hot and humid climate of equatorial regions. After rising in the atmosphere, the air moves poleward at high altitudes. As it travels toward 30° north and south latitudes, it cools further and becomes denser. Eventually, the air sinks around 30° latitude, creating high-pressure belts known as the Subtropical High Pressure Belts. These regions are associated with clear skies and dry conditions, which explain the existence of major deserts such as the Sahara Desert, Arabian Desert, and Australian Desert. The sinking air from the subtropical highs moves in two directions. One branch returns toward the Equator as surface winds. Due to the Coriolis effect, these winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. These winds are called Trade Winds. In the Northern Hemisphere, they blow from the northeast and are known as Northeast Trade Winds, while in the Southern Hemisphere they blow from the southeast and are called Southeast Trade Winds. The trade winds converge near the Equator, completing the Hadley Cell circulation.