Westerlies

The prevailing winds that blow from west to east in the middle latitudes of both hemispheres. They steer weather systems and vary with season and latitude.

Ferrel cell: The middle-latitude atmospheric circulation cell in each hemisphere, where surface air generally moves poleward. Its surface flow helps produce the westerlies between the Hadley and polar cells.
Extratropical cyclone: A rotating low-pressure weather system that develops outside the tropics along strong temperature contrasts. The westerlies steer these storms across the middle latitudes.
Trade winds: Persistent tropical surface winds that blow predominantly from east to west toward the equator. They lie equatorward of the westerlies and blow in the opposite direction.
Roaring Forties: The strong westerly winds commonly found in the Southern Hemisphere between about 40° and 50° south. This named belt shows how unobstructed Southern Ocean flow can intensify the westerlies.
Coriolis effect: The apparent deflection of moving objects caused by Earth’s rotation, directed oppositely in the two hemispheres. It turns poleward-moving air toward the east, giving the westerlies their prevailing direction.
Storm track: A common pathway followed by successive traveling storms in the atmosphere. Storm tracks often follow the strongest belts of westerly flow.
Polar easterlies: Cold, generally east-to-west surface winds found at high latitudes near the poles. They occupy the polar belts beyond the westerlies and reverse their prevailing direction.
Furious Fifties: The strong westerly winds commonly found in the Southern Hemisphere between about 50° and 60° south. They extend the Southern Hemisphere’s powerful westerly belt toward Antarctica.
Pressure gradient force: The force that accelerates air from regions of higher pressure toward regions of lower pressure. It drives the broad poleward flow that Earth’s rotation deflects into westerlies.
North Atlantic Oscillation: A fluctuation in the pressure difference between the subtropical Atlantic high and the Icelandic low. Its phases alter the strength and north–south position of North Atlantic westerlies.

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