Clouds are extremely complicated. Perhaps you are well acquainted with the complexity of clouds from lying on your back in the grass some fine summer day and studying their slow, graceful billowing movement across the sky, but clouds are complicated are extremely difficult to model properly, as well.

For one thing, they can cause either global cooling or global warming. Many clouds are white, so they reflect incoming radiation back into space, causing cooling. However, they are also rather opaque at the longer, thermal wavelengths where the Earth emits its strongest radiation. Thus they contribute to the greenhouse effect and cause global warming. Oftentimes, the effects of clouds depend on where in the atmosphere they are forming (tropospheric clouds? statospheric clouds?) On the Earth, the air tends to cool as you go upwards into the troposphere. At the boundary of the troposphere and the stratosphere, the trend reverses, and the heat goes up. You are losing the Earth's radiative heat, but you are approaching the ozone layer, which traps a large amount of radiation in the upper stratosphere (as a side note, the fact that the stratosphere has its hot layers above its cool layers means that it doesn't have to convect, which is why it's such a nice smooth place to fly planes). As you go further into the vacuum of space through the mesosphere, thermosphere, and exosphere, the temperature goes down again.
A lovely fellow here at the meeting has been working on something quite interesting� he has been modeling the effect of clouds on planets around other stars. Now some extra-solar planets can be seen with telescopes (the large ones) but the majority of planets can only be inferred by the gravitational effect they have on their parent star or the slight dimming of the star when the planet passes in front of it (occultation). Naturally we can�t tell if these planets have clouds at all, making the effort mainly a thought experiment. But the results are actually quite stunning: if you take a planet with an atmosphere like the Earth�s, and you place it at the distance from its star to deliver an Earth-like heat budget, you can isolate the effect that the dominant wavelength of the star has on what the clouds do. The size of the cloud particles do not change, you see, but since the wavelength of the light is changing, the degree to which the cloud particles scatter and reflect the incoming light changes- even the type of scattering that takes place can change. This leads to either a cooling or warming feedback loop that completely changes the thermal structure of the atmosphere, and the temperatures of the surface. Thus even if you lived at the absolutely appropriate distance from a star, even if you lived on a planet exactly like the Earth in every way, the fact that your star was an M star or whatever crazy kind of star would make your life completely different, even, perhaps, impossible.
One woman even took this consideration to determine what color plants would be on planets around extra-solar planets, and you could get purple plants or blue plants or any number of shades of planets as the plants would optimize the way they gathered their light. If humans existed there, they might see in a totally different wavelength range, because what we now call the �visible� spectrum is really just where the sun�s maximum light output is, making our eyes perfectly attuned to make maximum use of the energy that is available to us.

Re: Comment
clouds might be complicated and extremely difficult to model but they are beautiful in their own way n especially when clouds start to form a lil shape of something or show a vague figure of somethin or someone..its an interesting post!

in the end , i told her that she should go find out the answer herself rather than give space for some distortions in the process..
» AlexisNg on 2008-09-25 10:21:44

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