Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site utastro.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!genrad!mit-eddie!think!harvard!seismo!ut-sally!utastro!dipper From: dipper@utastro.UUCP (Debbie Byrd) Newsgroups: net.astro Subject: StarDate: July 11 Wind Message-ID: <333@utastro.UUCP> Date: Thu, 11-Jul-85 02:00:23 EDT Article-I.D.: utastro.333 Posted: Thu Jul 11 02:00:23 1985 Date-Received: Mon, 15-Jul-85 07:14:03 EDT Organization: U. Texas, Astronomy, Austin, TX Lines: 31 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