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Re: [Phys-l] Albedo and GW.


From: on behalf of John Denker
Sent: Mon 9/4/2006 5:51 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Albedo and GW.
1) Any patch of surface has its own radiative-equilibrium temperature, Tr.

2) A typical patch of surface in the arctic has an average temperature
*above* Tr, because of non-radiative heat "leaks" coming in from warmer
parts of the earth.

3) Therefore, each such patch is (on average) emitting more radiation than
it receives.


The data would indicate otherwise:

"A portion of the sunlight that reaches Earth is absorbed into the system, while some of the light is reflected by our planet back into space. Some of the sunlight that gets absorbed is converted to heat and later emitted by the surface and atmosphere back up into space. The term "net radiation" refers to the total amount of sunlight and heat energy that does not escape from the top of the Earth's atmosphere back into space. More precisely, net radiation is the sum total of shortwave and longwave electromagnetic energy, at wavelengths ranging from 0.3 to 100 micrometers, that remains in the Earth system. The image above is a false-color map showing the net incoming energy (in Watts per square meter) that was contained in the Earth system for the given month(s). Regions of positive net radiation indicate areas of energy surplus in the Earth system (i.e., green regions over the tropics) and areas of negative net radiation signify regions of energy deficit (such as blue regions over high latitudes and the poles)."


John also wrote:

Dry air is nearly transparent, in the IR as well as visible. You can
verify this for yourself by walking around in the high desert at night: skin
exposed to the sky feels cold, even if the air is not particularly cold.


Air has windows of transmission in the IR; some regions are quite opaque:

It is true that the wavelength range where room temperature bodies emit most of the IR (7.5-13 microns), air is quite transparent.

Larry Woolf
General Atomics