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Old 23rd June 2010, 02:56 AM   #34
Critical Thinker
Join Date: Apr 2007
Posts: 334
Originally Posted by wogoga View Post
So what is called greenhouse effect in the case of Venus is nothing more than atmospheric heat insulation over hundreds of millions of years. Gases are excellent insulators.

Originally Posted by ben m View Post
Nope. First of all, gases are excellent insulators against *conduction* and only conduction. Given convection and advection, over large distances they're actually worse insulators than solids.

Do you know evidence of significant vertical convection on Venus?

In heights where atmospheric temperatures are (significantly) influenced by the sun, there is strong horizontal convection (zonal circulation, transporting heat between the day and night sides of the planet). At lower than 50 latitudes, such east-west winds decrease from around 100 m/s at 60-70 km height to less the 1 m/s near surface.

Heat is also transported from the equator to the poles. However, near surface, such heat exchanges are not needed, as the temperature there does not depend on sun radiation, but on the iso-thermic heat from within the crust. (see)

And they're no insulation at all against radiation, except in the normal atmospheric-greenhouse-effect effect sense.

Also liquids and solid are "no insulation at all against radiation, except in the normal" not-being-transparent "sense".

To characterize a well-known normal physical principle by a trendy ideological concept such as greenhouse-effect seems rather problematic to me.

That Venus may seem hotter than expected, results primarily from the fact that planets with atmospheres have no clearly defined surfaces.

A black body with Venus' surface temperature (~740 Kelvin) radiates around 17,000 W/m2, whereas a black body with a temperature of Venus' upper cloud deck (~240 Kelvin) less than 200 W/m2.

If we defined the boundary between Jupiter's atmosphere and Jupiter's fluid interior as Jupiter's surface, then we also could explain its high temperature by a super greenhouse effect.

Cheers, Wolfgang

Ideology driven science is rather rule than exception
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