Global Wind Explained

The illustration listed below portrays the global wind belts, 3 in every hemisphere. Keep in mind that the U.S. Lies mostly in the Westerly Wind Belt through prevailing winds indigenous the west. Each of these wind belts represents a "cell" that circulates air through the setting from the surface ar to high altitudes and ago again. The cell on either side of the Equator are referred to as Hadley cells and give increase to the trade Winds in ~ Earth"s surface. Just how do we describe this pattern of global winds and also how go it influence precipitation?


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Figure 20. Worldwide Winds
Source: NASA

We"ll begin at Earth"s equator, whereby solar radiation is the greatest year around. Air near the equator is warmed and rises because it is less dense (mass/unit volume) than the air approximately it as shown in figure 21 below.

You are watching: Which global wind is indicated here


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Figure 21. Air close to the equator is heated and rises as indicated by the red arrows.
Source: Mike Arthur and also Demian Saffer

The increasing air creates a circulation cell, referred to as a Hadley Cell, in i beg your pardon the waiting rises and also cools in ~ high altitudes moves outside (towards the poles) and, eventually, descends ago to the surface. The continuous heating and also rise of air in ~ the equator produce low push there, which causes air to relocate (wind) in the direction of the equator to take it the ar of the air the rises. On the various other hand, sinking air create high press at the surface where it descends. A gradient of push (high come low) is formed that causes air to flow away indigenous the high and also towards the low press at the surface.


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Figure 22. Hadley Cells, displayed as red circles, are created as the wait rises.
Source: Mike Arthur and also Demian Saffer
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Figure 23. Hadley Circulation Cells cause a gradient the pressure shown in this figure.
Source: Mike Arthur and Demian Saffer

The planet would have actually two large Hadley cells if it did no rotate. But, because it does rotate, the rotation of the earth leads to the Coriolis effect. You should view the short video clip on this so-called "effect" or "force." (The Coriolis Effect). Without going into detail as to why rotation create this obvious force, the Coriolis effect reasons winds (and all relocating objects) to be deflected:

to the appropriate in the northern Hemisphereto the left in the southerly Hemisphere

The Coriolis effect causes winds come deflect together they take trip within circulation cells and also results in the two large hypothetical Hadley cells breaking right into six smaller sized cells, i m sorry looks something favor the diagram below (and the first figure in this series).


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Figure 24. The rotation the the earth is responsible for the Coriolis result which breaks the two huge Hadley Cells right into six smaller ones presented as 6 red circles in this figure.
Source: Mike Arthur and also Demian Saffer

Ok, so, we now have some idea about the beginning of an international wind systems that an outcome from push gradients at Earth"s surface. Just how does this produce precipitation, and also where? Precipitation occurs where moisture-laden waiting rises, either by heater at the equator or by running up and over a an ext dense air mass. Together the increasing air cools its volume to host water to reduce (relative humidity increases) and, at some point, saturation with respect to water vapor is reached. Then, condensation--clouds and also rain!


Figure 25. This number demonstrates how the wind move at the surface as it regarded Hadley cell circulation.
Source: Mike Arthur and Demian Saffer

The diagrams over and below portray just the Hadley cell circulation, the is thrust by heater in the equatorial region. On the surface, wind moves away from high press (High) and also toward low pressure (Low). Convergence occurs close to the equator (winds blow in towards one another) and also Divergence wake up under the descending wait that creates high-pressure belts. The final number (Figure 26) shows all 6 cells diagrammatically, together with the pressure variations in ~ the surface of the Earth and also zones of usual wet and also dry belts. Note particularly the dried belts near 30 degrees North and South.


Figure 26. This figure display divergent and also convergent winds as they concerned Hadley cabinet circulation.
Source: Mike Arthur and Demian Saffer
Figure 27. This figure shows all six cells diagrammatically, together with the press variations in ~ the surface ar of the Earth and also zones of usual wet and dry belts.
Click below for Text different of number 27.
Air circulation patternsLatitudeBarometric PressurePrecipitationSurface winds
90°HighDryDivergent
60°LowWetConvergent
30°HighDryDivergent
LowWetConvergent

Source: Mike Arthur and Demian Saffer
‹ worldwide Wind increase Unit 2: physical Hydrology ›
Earth 111: Water: Science and Society

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Modules


Unit 1: fresh Water: Scarcity or Surfeit?Module 2: Climatology the WaterRelative HumidityGlobal Wind

Authors: Michael Arthur and Demian Saffer Professors, The Pennsylvania State university - college Park, Patrick Belmont Assistant Professor, Utah State University.

Team Lead: Maureen Feineman, associate Professor, The Pennsylvania State University. Discovering Designer: April Millet, The Pennsylvania State University

This courseware module is component of pen State"s university of Earth and Mineral Sciences" OER Initiative.

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