Transcript The Geography and Climate of North America

The Geography and Climate of North America
Orography
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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)
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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
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The Cordillera consists largely of a 1.5-2 km plateau
with superimposed mountain ranges
Transport Pathways
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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
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North America is under the
influence of Pacific, Arctic and
Tropical air masses.
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Between 300-500 the the strong westerlies
and a more broken mountain barrier allows
maximum eastward transit of Pacific air.
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This ‘jet’ of westerly flow penetrating
NAM at mid-latitudes entrains and mixes
with air from the Arctic and the tropics.
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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 Flow
over North
America
January
NAVAIR, 1966
July
April
October