From: Longlake15@aol.com
Date: Sun Apr 06 2003 - 21:36:34 PDT
From: Longlake15@aol.com Message-ID: <30.3c1b2d79.2bc25a52@aol.com> Date: Mon, 7 Apr 2003 00:36:34 EDT Subject: Re: Pinhole Digest #1182 - 04/06/03
One of your questions about broad wind patterns on earth. Yes, the
atmosphere moves with the earth, however, primary wind patterns are a
combination of large convection cells and rotation of the earth.
Visualize each hemisphere and the atmosphere above it. On a stationary
earth, air heats more at the equator than the poles. So, warm air at the
equator rises into the atmosphere and is replaced by colder air moving toward
the equator from the poles. This creates a large convection cell of air
moving across the earth's surface and warming as it moves to rise high into
the atmosphere at the equator. With the additional factor of arctic air (90
degrees North/ south) warming as it flows to the equator. By the time it
gets to about 60 degrees it has warmed and rises, rather than going all the
way to 90 degrees. Think also of equatorial air cooling as it moves north/
south. By the time it gets to about 30 degrees it has cooled enough to sink.
When it sinks and contacts the earth's surface, it can move to the poles or
to the equator as cool air. So it does both, completing a "cell" from 30
degrees to the equator - the basis for the easterly trade winds (blowing from
the east). Another "cell" is created from 30 degrees to 60 degrees as cool
air is warmed as it moves north/ south - the basis for the temperate
westerlies. Then when it gets to 60 degrees, it joins warm air moving from
the arctic regions. The third "cell" in each hemisphere is the easterly
polar winds.
The air moving across the earth within each of these cells experiences the
coriolis effect - moving at the same speeds as its origin, but getting caught
behind (slower than the earth's surface as it moves toward the equator -
hence easterlies) or moving faster than the earth's surface as it moves
toward the poles - hence westerlies.
This is better explained with 3 d models, pictures or sketches and is found
in most basic earth science and/ or physical science texts. Or ask most any
sailor. Hope this helps. Good luck.
Warren Long (Drew School)
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