1987 Edition

Westerlies, middle-latitude west winds

  • Jay R. Harman
Reference work entry

The term westerlies refers to the zone of winds poleward from the subtropical high-pressure belt, present in both the Northern Hemisphere and Southern Hemisphere, that is characterized by migratory cyclones and anticyclones traveling generally west to east. Usually located poleward from approximately 35°N and S latitude, the westerlies extend much of the remainder of the distance to the poles and are developed to levels exceeding the height of the tropopause.

Energy Sources and Role in the General Circulation

The principle source of energy of the westerlies is the meridional (south-north) thermal gradient between the warm subtropical atmosphere and the colder polar atmospheres. This horizontal thermal gradient (a situation referred to as baroclinicity) arises because of the nonuniform distribution of annual solar radiation inputs into the global Earth-atmosphere system; it results in lowerpressures at given tropospheric heights in the colder polar atmospheres than near the equator as...
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Copyright information

© Van Nostrand Reinhold 1987

Authors and Affiliations

  • Jay R. Harman

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