Tropospheres of Earth and Mars, Why does air temperature decrease with altitude? |
Tropospheres of Earth and Mars, Why does air temperature decrease with altitude? |
Aug 14 2010, 11:02 AM
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Junior Member Group: Members Posts: 55 Joined: 6-March 10 From: Cincinnati, OH Member No.: 5246 |
What causes the lapse rate in the tropospheres of Earth, Mars, and Venus?
I used to think that it was because thinner air has a lower heat capacity and absorded less radiation (both incoming short-wave from the Sun and outgoing infrared). But I've also read that air at high altitudes is cooler because it is farther from the ground (i.e, it is less warmed by the infrared-emitting surface). This makes sense if you're in a balloon or airplane, but what about on a wide, high plateau where you're on the ground. Isn't the air is still cooler there than at sea level? Without going into dry vs. wet lapse rates or effects of convection, is there a simple answer to this question that a fifth grader could understand? Tom |
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Sep 10 2010, 12:16 PM
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Junior Member Group: Members Posts: 57 Joined: 13-February 06 From: Brisbane, Australia Member No.: 679 |
What causes the lapse rate in the tropospheres of Earth, Mars, and Venus? I used to think that it was because thinner air has a lower heat capacity and absorded less radiation (both incoming short-wave from the Sun and outgoing infrared). But I've also read that air at high altitudes is cooler because it is farther from the ground (i.e, it is less warmed by the infrared-emitting surface). This makes sense if you're in a balloon or airplane, but what about on a wide, high plateau where you're on the ground. Isn't the air is still cooler there than at sea level? Without going into dry vs. wet lapse rates or effects of convection, is there a simple answer to this question that a fifth grader could understand? Tom Hi Tom Assuming you haven't found an answer - which an enterprising 10 year old probably would have by now - I can simply say that air loses heat as it gets higher because it gets tired on the way up. Though that sounds facetious I'm serious. Energy is lost as air rises under the effect of gravity - it has to climb against the drag of gravity, which means energy is expended. |
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Sep 10 2010, 03:13 PM
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Director of Galilean Photography Group: Members Posts: 896 Joined: 15-July 04 From: Austin, TX Member No.: 93 |
I'd say it's also due to the greenhouse effect. Less air above you to help keep heat in. Think of a clear night vs a cloudy night. Those clouds do a great job of keeping the ground warm. But even on a clear, still night the air above you helps somewhat to keep you warmer, and at high altitudes there is less of it.
-------------------- Space Enthusiast Richard Hendricks
-- "The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke Mother Nature is the final inspector of all quality. |
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Sep 10 2010, 04:03 PM
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Member Group: Members Posts: 293 Joined: 29-August 06 From: Columbia, MD Member No.: 1083 |
The adiabatic lapse rate (-9.8K/km on Earth) is just acceleration due to gravity over the specific heat at constant pressure (cp). That's true for other planets as well. On Earth, you get an inversion (warming with height) in the stratosphere and the thermosphere because of enhanced radiative absorption from ozone and atomic oxygen, respectively. Mars doesn't have a true stratosphere and doesn't have any large region in the middle atmosphere that temperatures warm with height until you reach the thermosphere. Titan has a distinct troposphere, stratosphere, etc...
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Sep 12 2010, 08:31 AM
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Junior Member Group: Members Posts: 55 Joined: 6-March 10 From: Cincinnati, OH Member No.: 5246 |
Thanks everybody.
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