The Geography and Climate of North America

Orography

• The Cordillera, extensive system of mountain ranges stretching from Alaska , through British Columbia, Sierra Nevada, the Coast and Cascade ranges, and the Rocky Mountains and the Sierra Madre in Mexico.

The Climates of North America ( Based on Bryson and Hare, 1974)

• The dominant geographic features of N. America are the high Cordillera and the eastern Lowlands

• The Cordillera is a most significant obstacle to the zonal westerly and to the easterly trade winds

• The plains allow unobstructed path to great meridional excursions of both Arctic and Tropical air masses

• The Cordillera consists largely of a 1.5-2 km plateau with superimposed mountain ranges

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Transport Pathways

• Low level westerly winds impinging on the Cordillera barrier are mostly deflected, some pass through to the Plains

• At about 500 N the low-level westerly zonal flow divides into northerly and southerly branches along the western slopes.

• There are three main routes for the low-level westerlies to cross the Cordillera; the most notable is the Columbia-Snake-Wyoming Channel.

• In Mexico, the southward deflected westerlies usually do not cross the Sierras.

• Over the Gulf of Mexico, the low level easterly the trade winds are usually deflected northward.

• South of the Yucatan, the trade winds cross the continent and turn southward.

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Features of Air Flow over North America

• North America is under the influence of Pacific, Arctic and Tropical air masses.

• Between 300-500 the the strong westerlies and a more broken mountain barrier allows maximum eastward transit of Pacific air.

• This ‘jet’ of westerly flow penetrating NAM at mid-latitudes entrains and mixes with air from the Arctic and the tropics.

• This unique distribution of land, sea and mountains produces a highly variable weather: From one day to another, mild, sunny air from the Rocky Mountains may replace moist, warm, cloudy tropical air and then give way to cold Arctic air.

Seasonal Air Flowover North

America

NAVAIR, 1966

January

OctoberJuly

April