DMPQ- . Discuss the types of cells formed primary wind circulations.

. The trade winds, westerly and easterlies  are the permanent winds. These blow constantly throughout the year in a particular  direction and they are global in nature.  These play an important role in, and in turn get influenced too, formation of Weather  Cell.

Headly Cell

The air at the Inter Tropical Convergence Zone (ITCZ) rises because  of convection caused by high insolation and a low pressure is created. The winds  from the tropics converge at this low pressure zone. The converged air rises  along with the convective cell. (as in the figure, Headly Cell) It reaches the top of  the troposphere up to an altitude of 14 km. and moves towards the poles. This  causes accumulation of air at about 30o N and S. Part of the accumulated air  sinks to the ground and forms a subtropical high (denoted as STH in fig).  Another reason for sinking is the cooling of air when it reaches 30o N and S  latitudes.

Down below near the land surface the air flows towards the equator as the  Easterlies or Trade Winds. The easterlies from either side of the equator  converge in the Inter Tropical Convergence Zone (ITCZ). Such circulations from  the surface upwards and vice-versa are called cells. Such a cell in the tropics is  called Hadley Cell. This is a hot cell, while polar cell is a colder cell.

Ferrel Cell

In the middle latitudes the circulation is that of sinking cold air that  comes from the poles and the rising warm air that blows from the subtropical  high. At the surface these winds are called WESTERLIES and the cell is known as  the Ferrel cell.

Polar Cell

At polar latitudes the cold dense air subsides near the poles and  blows towards middle latitudes as the polar easterlies. This cell is called the  polar cell.

These three cells set the pattern for the general circulation of the atmosphere.  The transfer of heat energy from lower latitudes to higher latitudes maintains  the general circulation.


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