Naked Science Forum
Life Sciences => The Environment => Topic started by: Anastasia.fr.1 on 06/08/2007 20:00:59
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In a dirty place [lots of dust and dirt !] how does the wind go so far down to lift up the dirt up. Because the wind is normly in the air with the clouds ! [???]
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Wind most certainly does come down to ground level as anyone living in Chicago can verify!
There are various layers in the atmosphere that have wind. Wind at ground level doesn't necessarily have to blow in the same direction as wind higher up.
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Thank you. so where does the wind come from ?
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Over there --->
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My basic answer (because I don't actually know any more than this) is that wind is the result of air masses moving from areas of high pressure to low pressure, in the same way that air rushes into a vacuum. There are various effects that cause these changes in pressure and direction of spin of the weather system - heating of the air, the spin of the earth (the Coriolis Effect, though please don't ask me how it works!) - high pressure tends to be associated with calm weather as you have a heavy air mass above you which is just sort of sitting around. Low pressure tends to be associated with stormy weather, as lots of air is rushing in. I'm sure there's someone out there who can give a rather more scientific answer though!
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(the Coriolis Effect, though please don't ask me how it works!)
Basic reason is easy to understand: Let's assume we're dealing with the Northern Hemisphere.
The lines of latitude (the East- West ones) get shorter and shorter as you go North.
Someone standing on 500 N line is going Eastwards faster than someone standing on the 600 N line because they are both going round once a day.
If you move from 50 N to 60N, your speed will carry you Eastwards, relative to someone standing on 60N. Likewise, someone moving Southwards from 60N to 50N will find themselves carried Westwards.
You can try this on a kids' playgound roundabout - you really do feel a force as you try to move in or out from the centre.
You are only allowed to try this if you are under 11 years of age, though - the park keeper may chase you off.
Any air, travelling North / South will be forced to follow a curved path due to this effect. This can cause whirlwind- type of motion or 'vortex'. in moving air.
There is natural convection of air up from the equator and down at the poles - and some circulation in between, too. Coriolis causes the convection currents to be twisted and the various bands of air show a sort of herring bone pattern in their directions of flow.
The low pressure areas tend to be caused where two streams of air brush against each other and the Coriolis effect accentuates the vortex effect, which, in turn, tends to lower the pressure further with increasing wind speed. These Depressions are very dynamic structures and tend to dart about in a chaotic fashion.
High pressure is where there is a large mass of air which is relatively still. You get stable weather there because it tends to deflect any approaching depressions.
The UK sits at a latitude where the cool northerly air mass is rubbing shoulders with the warm, wet southerly mass - hence the naff weather - except when there is a 'high' over us.
I recently read a couple of books about Met in connection with a Navigation Course. Fascinating. and it ties in with good ol' Physics quite well.
But dentstudent's explanation is certainly near enough for jazz.