Westerlies

The westerlies are the prevailing surface winds of the mid-latitudes, blowing from west to east between roughly 30 and 60 degrees in both hemispheres. They are the surface branch of the Ferrel cell, flowing poleward from the subtropical highs and turned eastward by the Coriolis force, and they steer the procession of extratropical cyclones along the polar front. In the Southern Hemisphere, with little land to add friction, they blow strongest as the Roaring Forties. The overlying westerly jet stream meanders as Rossby waves, and the strength of the belt is indexed by the Arctic and Southern Annular modes.