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Author Topic: Why does the wind blow?  (Read 3384 times)

Offline thedoc

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Why does the wind blow?
« on: 20/05/2013 12:14:40 »

I want to know, what is wind? Not the type you get from eating lots of baked beans(Ha! Ha!) but the one that we feel on our face and in the trees. I want to know whether it is all gases that make up our atmosphere or something else? Where does it come from or go and what is giving its energy/driving it? what is solar wind?

Await your response.

Many thanks,

Pradip Patel
Asked by Rohit Patel

                                        Visit the webpage for the podcast in which this question is answered.

 ...or Listen to the Answer or [download as MP3]

« Last Edit: 20/05/2013 12:14:40 by _system »


Offline Lmnre

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Re: What is wind?
« Reply #1 on: 12/05/2013 16:26:04 »
A picture is worth a thousand words (and the thickness of the Earth's atmosphere shown below is greatly exaggerated in order to show the circulating air).

As you will read, wind doesn't merely go from here to there but basically goes around and around in various ways, and it is powered by the Sun!

Compared to the rest of the Earth, the equatorial regions (that is, near 0 latitude) receive the greatest amounts of the Sun's rays specifically its thermal rays, which is why I did not call it sunlight. The equatorial regions then heat the air above them more than elsewhere, and this difference causes the air there to rise more than elsewhere. This causes a chain reaction that results in what scientists call Hadley Cells (see diagram above). The physics of everything involved here limits the length of Hadley Cells to about 30 latitude.

The same difference in heating also occurs between about 60 and the nearby poles, causing what scientists call Polar Cells. Between these two kinds of cells (that is, between 30 and 60) are what scientists call Ferrel Cells, but they rotate in the opposite direction because the Hadley and Polar Cells have more effect on the air there than does the Sun's rays. If you think of all these cells as gears, then you can see why the Ferrel Cells turn opposite to what the Sun's energy would drive them to do.

As the air in these cells gain altitude, the physics involved causes the water in them to fall out, which causes more rain in the tropics than elsewhere. This also tends to make the air over the 30 latitudes rather dry, and so little rain falls there, which in turn causes the major deserts to form in those regions (see diagram below). (Everything happens for a reason!)

Another physical phenomena, called the Coriolis Effect, causes the movement of air at the surface to deviate from their simple north-south directions and adds an east-west component to the direction of the winds in the various regions (see diagram below) that is, adding an easterly component to the tropical and polar winds, which travel toward the direction of the equator, and a westerly component to the temperate winds, which travel in the direction away from the equator. Keep in mind that the names of winds indicate where they seem to be coming from, not going toward. So, for example, the northeast winds in the northern tropics come from the northeast and move toward the southwest.

So there you have the general global wind patterns. Our ability to predict the wind and weather is limited due to the complexity of all the physics involved, although computers especially supercomputers which can "crunch" more data more quickly than is humanly possible, now give us the ability to predict wind and weather more accurately several days into the future and beyond.
« Last Edit: 20/06/2013 06:49:11 by Lmnre »

Online yor_on

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Re: Why does the wind blow?
« Reply #2 on: 01/06/2013 14:37:19 »
Very nice description Lmnre.

The Naked Scientists Forum

Re: Why does the wind blow?
« Reply #2 on: 01/06/2013 14:37:19 »


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