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80 FUNDAMENTALS OF PHYSICAL GEOGRAPHY climate. A schematic description of the general The general circulation of the atmosphere circulation is shown in Figure 9.6. also affects the oceans. The large-scale winds of the atmosphere initiate large and slow moving currents of the ocean. Oceans in turn provide input of energy and water vapour into the air. These interactions take place rather slowly over a large part of the ocean. General Atmospheric Circulation and its Effects on Oceans Warming and cooling of the Pacific Ocean is most important in terms of general atmospheric circulation. The warm water of the central Pacific Ocean slowly drifts towards South American coast and replaces the cool Peruvian current. Such appearance of warm water off the coast Figure 9. 6 : Simplified general circulation of Peru is known as the El Nino. The El of the atmosphere Nino event is closely associated with the pressure changes in the Central Pacific The air at the Inter Tropical Convergence and Australia. This change in pressure Zone (ITCZ) rises because of convection caused condition over Pacific is known as the by high insolation and a low pressure is southern oscillation. The combined created. The winds from the tropics converge phenomenon of southern oscillation and at this low pressure zone. The converged air El Nino is known as ENSO. In the years rises along with the convective cell. It reaches when the ENSO is strong, large-scale the top of the troposphere up to an altitude of variations in weather occur over the 14 km. and moves towards the poles. This world. The arid west coast of South causes accumulation of air at about 30 N and America receives heavy rainfall, drought S. Part of the accumulated air sinks to the occurs in Australia and sometimes in ground and forms a subtropical high. Another India and floods in China. This reason for sinking is the cooling of air when it phenomenon is closely monitored and is reaches 30 N and S latitudes. Down below used for long range forecasting in major near the land surface the air flows towards the parts of the world. equator as the easterlies. The easterlies from either side of the equator converge in the Inter Seasonal Wind Tropical Convergence Zone (ITCZ). Such circulations from the surface upwards and The pattern of wind circulation is modified in vice-versa are called cells. Such a cell in the different seasons due to the shifting of regions tropics is called Hadley Cell . In the middle of maximum heating, pressure and wind belts. latitudes the circulation is that of sinking cold The most pronounced effect of such a shift is noticed in the monsoons, especially over air that comes from the poles and the rising southeast Asia. You would be studying the warm air that blows from the subtropical high. At the surface these winds are called westerlies details of monsoon in the book India : Physical and the cell is known as theFerrel cell. At polar Environment (NCERT, 2006). The other local latitudes the cold dense air subsides near the deviations from the general circulation system poles and blows towards middle latitudes as are as follows. the polar easterlies. This cell is called the polarLocal Winds cell. These three cells set the pattern for the general circulation of the atmosphere. The Differences in the heating and cooling of earth transfer of heat energy from lower latitudes to surfaces and the cycles those develop daily or higher latitudes maintains the general annually can create several common, local or circulation. regional winds. Reprint 2026-27