Wind movement in the atmosphere may be classified into three broad categories: primary circulation, secondary circulation, and tertiary circulation. Primary circulation includes the planetary wind systems which are related to the general arrangement of pressure belts on the earth’s surface.
Trade winds, westerlies and polar easterlies together form the primary circulation. In fact, it is the primary circulation patterns which prepare the broad framework for the other circulation patterns.
Secondary circulation consists of cyclones, anticyclones, monsoons, and air masses. Tertiary circulation includes all the local winds which are produced by local causes and which only affect the weather and climate of a particular locality or area.
It may be pointed out that the above classification of atmospheric motions is based on the time and space scales. The largest-scale wind movement is also referred to as macro-scale circulation which represents the mean airflow over the entire globe.
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The term ‘synoptic scale circulation’ is used for secondary circulation. Mesoscale and microscale circulations represent the tertiary circulation which includes the local winds as well as other atmospheric turbulences.