Re: [Phys-l] Greenhouse effect / 2nd law

["LaMontagne, Bob" <RLAMONT@providence.edu>]

This ignores the huge positive thermal gradient just above the ground - an inversion after hours of radiational cooling. The only significant condensation is right at the ground (unless radiational fog forms). The unsaturated vapor above sends IR back to the ground keeping temperatures a touch warmer as JD states.

Bob at PC

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From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] on behalf of Dan Schroeder [dschroeder@weber.edu]
Sent: Tuesday, April 26, 2011 5:46 PM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] Greenhouse effect / 2nd law

On Apr 25, 2011, at 6:47 pm, John Denker wrote:

> If/when there is some humidity in the air, nighttime temperatures
> do not drop nearly so much.

Although the greenhouse effect plays a role here, I think the more important factor is condensation. Once the temperature drops to the dew point, further heat loss merely causes more water vapor to condense, with little effect on air temperature.

Dan

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