Global Wind Patterns
PHYSICAL GEOGRAPHY 101

Ideal Global Wind Patterns

Start with an ideal globe model - no surface features, no seasons
Examine the ideal globe model in the textbook.

Intertropical Convergence Zone (ITC)

Incoming solar radiation will be most intense at the equator - warms air at the equator.
Warm air will rise, creating a low pressure center.
Surrounding air will move into the equatorial region, into the low pressure area - this air in turn is heated by insolation and rises.
Air converges at the equator - Intertropical Convergence Zone (ITC).
This belt is also known as the Doldrums - surface winds are weak and variable - air movement is primarily vertical.

Hadley Cells

Warm air at the equator rises, then moves poleward.
Cools and descends at ~30° Latitude, creating a high pressure area.
Air moves out of the high pressure centers towards the equatorial low pressure centers completing a circulation cell known as a Hadley Cell.

Subtropical High Pressure Belt

The high pressure areas at ~30° Latitude is called the Subtropical High Pressure Belt.
Within theses belts (there are 2, one in the northern hemisphere and one in the southern) 2 to 4 large, stable anticyclones develop.
Winds are weak and variable - air movement is primarily vertical.
This area is also known as the Horse Latitudes.

Prevailing Westerlies

Poleward of the Subtropical High Pressure Belt are the Prevailing Westerlies. Air movement out of the high pressure centers into the mid-latitudes is out of the west.
Tend to be found between 30-60° Latitude.
This region is complicated by the Polar Front.

Polar Front

Polar regions, with very cold air, tend to be high pressure center.
Air movement will be away from the poles towards the mid-latitudes.
Air in the Subtropical High Pressure Belt is hot and moving away from the tropics towards the mid-latitudes.
These two conflicting air masses, one hot, one cold, meet at the Polar Front.

Ferrel and Polar Cells

Along the Polar Front, the warm air, being less dense, will rise over the cold air.
Some of this air returns at high altitude to the region above the Subtropical High Pressure Belt completing what is known as the Ferrel Cell.
Some of this air continues poleward completing the Polar Cell circulation.

Class Discussion of Actual Global Wind Patterns

Monsoons

The Monsoons in Southern and Southeastern Asia are the result of a number of factors.
1) extreme movement of the ITC in Asia - no similar shifts occur elsewhere in the world
- results in a reversal of wind direction between summer and winter.
2) location, and size of the Himalayas Mountains
3) location of the Indian Ocean
In January, the wind direction is from the northeast, out of the Siberian High pressure center
- this is cold, very dry air.
This cold, dry air runs into the Himalayas.
What happens to it? Think in terms of orographic precipitation.

In July, the air mass is coming from the Indian Ocean, a southwest wind - this is very warm, very moist air.
This warm, moist air runs into the Himalayas. What happens to it?

Local Winds

1) Sea-Land breezes
2) Mountain winds - mountain barriers cause variable wind directions, updrafts and downdrafts are common
3) Drainage winds - cold air flows downward often following valleys
4) Chinook winds - warm, dry, leeward winds associated with the orographic precipitation process.

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