dipper@utastro.UUCP (Debbie Byrd) (07/11/85)
The air surrounding our planet Earth is always in motion. We'll talk more about the wind -- when we come back. July 11 Wind On our planet Earth, the wind is always blowing somewhere. So the wind must ve a constantly renewable source of energy. It turns out that the wind stems from the ultimate energy source of almost everything on Earth -- the sun. Here's why the wind blows. Sunlight shines on the Earth, and warms the air and the ground. Warm air expands -- and pretty soon the air near the ground gets warm enough to expand and rise. New air flows in along the ground to take its place -- and that flow of air is what we call wind. In the lower atmosphere, where we are, wind speed tends to increase with altitude. If you live in the city, you probably know that the wind blows harder at the top of tall buildings than it does near the ground. The wind near the ground is slowed down by friction with the surface of the Earth. That's the general rule -- but it's actually the case that on summy or rainy days, fast-moving air from the upper atmosphere moves down toward the ground to increase the speed of the wind. If the atmosphere is stable, the fast-moving air stays up high. That's why, in a fog or at night, the wind usually blows very softly -- or not at all. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin
lhl@lanl.ARPA (07/11/85)
> > On our planet Earth, the wind is always blowing somewhere. So the wind > must ve a constantly renewable source of energy. It turns out that the > wind stems from the ultimate energy source of almost everything on > Earth -- the sun. > *** OPUS LIVES !!! *** Which is puzzling: since the air is heated in the morning, and cools in the evening, why isn't there a constant wind (shock wave, actually) at the speed of the earth's rotation?
peterb@pbear.UUCP (07/17/85)
>> >> On our planet Earth, the wind is always blowing somewhere. So the wind >> must ve a constantly renewable source of energy. It turns out that the >> wind stems from the ultimate energy source of almost everything on >> Earth -- the sun. >> > > Which is puzzling: since the air is heated in the morning, and >cools in the evening, why isn't there a constant wind (shock wave, >actually) at the speed of the earth's rotation? >/* Written 11:52 am Jul 11, 1985 by lanl!lhl in pbear:net.astro */ At sunrise the sun has to pass through a thicker layer of air to heat it since the atmosphere is thickest(in relation to the sun's direction) when the sun is on the horizon. So the amount of energy is spread over a larger amount of air. As the earth rotates, the air layer thins, and the amount of energy per unit air volume increases. After the sun passes through the 12 O'clock position, the air layer thickens, and the energy per unit volume decreases. Since the energy function is smooth (except at sunset/sunrise, and there the discontinuity is low), a shock wave would be quite small, if noticable at all. Also with the mass of the air itself, the shock wave would be absorbed by the nearby air particles. Peter Barada {ihnp4!inmet|{harvard|cca}!ima}!pbear!peterb
connolly@steinmetz.UUCP (C. Ian Connolly) (07/20/85)
> > > > On our planet Earth, the wind is always blowing somewhere. So the wind > > must ve a constantly renewable source of energy. It turns out that the > > wind stems from the ultimate energy source of almost everything on > > Earth -- the sun. > > > > *** OPUS LIVES !!! *** > > Which is puzzling: since the air is heated in the morning, and > cools in the evening, why isn't there a constant wind (shock wave, > actually) at the speed of the earth's rotation? Off the top of my head, I'd say it's because friction and the viscosity of the atmosphere prevent such a thing from occurring - a damping of the shockwave, in effect. In addition, convection is a vertical movement - what goes up must come down, & density fluctuations due to water vapor probably prevent such flows from being orderly & in lockstep with earth's rotation. Then there are orographic effects, such as mountains, and varying albedo (snow fields absorb less energy than blacktop). It's a physicist's nightmare. -- C. Ian Connolly, WA2IFI - USENET: ...edison!steinmetz!connolly , , ARPANET: connolly@ge-crd An rud a bhionn, bionn.