Global Wind Explained

The illustration listed below portrays the global wind belts, three in every hemisphere. Keep in mind that the U.S. Lies mostly in the Westerly Wind Belt v prevailing winds native the west. Each of these wind belts represents a "cell" that circulates air with the atmosphere from the surface to high altitudes and ago again. The cells on either next of the Equator are called Hadley cells and also give climb to the profession Winds at Earth"s surface. How do we describe this pattern of worldwide winds and also how walk it affect precipitation?


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Figure 20. Global Winds
Source: NASA

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

You are watching: Which global wind is indicated here


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

The rising air creates a circulation cell, called a Hadley Cell, in i beg your pardon the waiting rises and cools at high altitudes moves external (towards the poles) and, eventually, descends back to the surface. The continual heating and rise that air in ~ the equator create low pressure there, which reasons air to move (wind) towards the equator to take the ar of the air that rises. ~ above the other hand, sinking air creates high pressure at the surface ar where it descends. A gradient of press (high to low) is formed that reasons air to flow away indigenous the high and also towards the low press at the surface.


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

The earth would have two big Hadley cells if the did not rotate. But, because it go rotate, the rotation that the planet leads to the Coriolis effect. You must view the short video on this so-called "effect" or "force." (The Coriolis Effect). Without going right into detail as to why rotation create this obvious force, the Coriolis effect reasons winds (and all relocating objects) to it is in deflected:

to the right in the northern Hemisphereto the left in the southern Hemisphere

The Coriolis effect reasons winds to deflect together they take trip within circulation cells and results in the two large hypothetical Hadley cells breaking into six smaller sized cells, which looks something prefer the diagram listed below (and the an initial figure in this series).


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Figure 24. The rotation of the earth is responsible because that the Coriolis impact which breaks the two big Hadley Cells right into six smaller ones presented as six red one in this figure.
Source: Mike Arthur and also Demian Saffer

Ok, so, we now have some idea around the origin of global wind equipment that result from pressure gradients at Earth"s surface. How does this develop precipitation, and also where? Precipitation occurs wherein moisture-laden air rises, one of two people by heater at the equator or by to run up and over a much more dense air mass. As the climbing air cools its capacity to organize water reduce (relative humidity increases) and, at part point, saturation v respect to water vapor is reached. Then, condensation--clouds and rain!


Figure 25. This number demonstrates just how the wind moves at the surface ar as it regarded Hadley cabinet circulation.
Source: Mike Arthur and also Demian Saffer

The diagrams over and listed below portray just the Hadley cabinet circulation, that is driven by heater in the equatorial region. Top top the surface, wind moves far from high push (High) and also toward low press (Low). Convergence occurs close to the equator (winds punch in in the direction of one another) and Divergence occurs under the descending wait that creates high-pressure belts. The final number (Figure 26) mirrors all six cells diagrammatically, along with the pressure variations in ~ the surface ar of the Earth and also zones of common wet and also dry belts. Note specifically the dried belts close to 30 levels North and South.


Figure 26. This figure present divergent and also convergent winds together they pertained to Hadley cabinet circulation.
Source: Mike Arthur and Demian Saffer
Figure 27. This figure shows all 6 cells diagrammatically, in addition to the pressure variations in ~ the surface of the Earth and zones of usual wet and dry belts.
Click right here for Text alternate 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: new Water: Scarcity or Surfeit?Module 2: Climatology that WaterRelative HumidityGlobal Wind

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

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

This courseware module is part of penn State"s university of Earth and also Mineral Sciences" OER Initiative.

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