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Global Wind Patterns

Objectives:    

    1.    Identify factors that affect global wind patterns.

    2.    Describe the strengths and weaknesses of the three-celled circulation model, and use the model to describe prevailing winds and pressure  regions.

Key Terms:

    polar front        mid-latitude        ITCZ        trade winds        prevailing winds

Notes: (19-3)

Wind is a vital resource.  It turns generators that power cities, provides opportunities for sport, and is affects commerce as ships sail from port to port.  Understanding the global wind patterns can be both advantageous and necessary for industry that depend on the wind's energy.  To understand the global wind patterns it is best to first view the Earth as a fixed (non rotating) planet.

Hadley cells(www.bom.gov.au/info/ftweather/ images/hadley3.gif)

As you can see in the absence of the Coriolis effect the cold air from the poles and the warm air from the equator create 4 distinct convection cells.   Because the Earth rotates on its axis these large cells do not actually form.

Descending air is deflected to the right breaking the large convection current into 3 distinct cells
The winds cells are created as alternating highs and lows occur

 

(www.ace.mmu.ac.uk/.../Weather_Climate/ images/03c.jpg)

Polar high - Climate is cold and dry - cold dense air sinks toward the polar front to 60o
Polar Front - Climate is cool and moist - cool moist air rises and circulates toward the subtropic high at 30o
Subtropic high - Climate is warm and dry - warm dry air sinks toward the equatorial low at 0o
Equatorial low - Climate is warm and moist - air is circulated back up to the subtropic high 
Intertropical convergence zone (ITCZ)- area of warm moist air that often does not have winds.  Called the doldrums.

 

(geoweb.tamu.edu/courses/geol101/ grossman/Air.circulation.jp)

Winds are always named after the direction of origin (think of the wind vein).  The direction of the convection sets up the direction of the wind.

Polar high - Polar N.Easterlies
Polar Front - Prevailing S.Westerlies
Subtropic high - Prevailing N.Easterlies
Equatorial low - Trade winds

 

It is important to know that this is an oversimplified model and that factors alter what is predicted in the 3-cell model.  The main causes of the deviation would be:

insolation 
proximity to water 
transient high and low pressure systems

 

 

 

Last modified: January 05, 2004