Re: Erdatmosphäre wird geringer?
Geschrieben von detlef am 20. September 2004 00:17:26:
Als Antwort auf: Erdatmosphäre wird geringer? geschrieben von Guerrero am 19. September 2004 21:05:20:
hallo,
ich hab da was gefunden:
http://astro.uchicago.edu/cara/southpole.edu/qanda/qa_outdoors.html
danach soll ueber beiden polen duenne kalte luft von oben herunter fallen. (als ausgleich fuer heisse luft, die ueber'm aequator hochsteigt)
gruss,detlef
Your website says the South Pole site is at 2,900 meters, but the actual air pressure is closer to 3300- 4000 meters - I was wondering why..? Is that due to the Earth's rotation?
This is a good question, but the answer is a little complicated. You probably know that hot air rises and cold air sinks. So, you might imagine that the hot air heated over the equator rises, and sinks as it moves towards the Poles. That's pretty much what happens, except the real Earth has mixtures of water and land, it's rotating, and the Sun is not exactly over the equator all the time. Here's a website I found with some useful pictures: http://www.uea.ac.uk/~e930/e174/l7_atmc.html The "Hadley Cell" picture demonstrates the heating/cooling cycle. The "real Hadley Cell" picture demonstrates something closer to what really happens, but note that it only reaches to 40 degrees north and south - this is a result of land and water disrupting the pattern. The "surface winds" picture shows more clearly the answer to your question. Note that both the poles have a permanent high pressure center sitting over them. This cold, lower-density air crashing down on the poles makes the effective altitude higher than the actual altitude. In the case of the South Pole, the large continent doesn't moderate the airflow as the water would, so it's REALLY cold and PERMANENTLY high pressure, and all of that air from the upper alitudes crashing down is so cold and from so high that it is thin, and this works out to make the effective altitude much higher. This high pressure center is also what makes it so dry at the South Pole -- the air that is crashing down has already had all the moisture taken out elsewhere.
The reason the arrows in that "surface winds" picture don't just go straight north and south, the reason they curve, is due to rotation (called the coriolis force), but that is not why the South Pole has a permanent high pressure center. This Coriolis force is also what makes hurricanes in the northern hemisphere rotate one way, while their counterparts in the southern hemisphere go the other way.