crapworks said:
Hey guys, I'm aware that atmospheric temperature gradients causes changes in bouyancy so hot air goes up and cold air goes down and immediately fills in the 'void' the hot air left, thus causing wind.
What about in zero/micro gravity, how does temperature gradients in air behave? Will the differences in kinetic molecular speeds in temperature gradients still cause wind or none at all? How strong or how weak the wind will be if there are any and what direction (hot to cold or vice versa)?
i tend to agree with Andy if we stick to your specific interpretation of convection as the movement of air molecules differing in temperature directly toward or away from a source of gravity. that is, there is very little convective flow in orbit b/c there is very little gravity, and that there is no convective flow in absolute zero gravity. simply b/c the convection of air relies on both the existence of temperature gradients AND gravity.
but even if there is no convection (air movement directly toward or directly away from some source of gravity) to induce wind in a zero-gravity environment, wind can be induced via temperature gradients in other ways. remember that atmospheric temperature gradients also cause atmospheric pressure gradients. and these pressure gradients not only result in air movement directly toward or away form the center of the earth, but also air movement more or less parallel to the surface of the earth. this is why air from high-pressure systems spreads out and flows in the direction of adjacent low-pressure systems. so not only is wind on Earth caused by the movement of air perpendicular to the Earth's surface (convection), but also by the movement of air parallel to the Earth's surface (pressure differentials). for a specific example, imagine that there is a high-pressure system over the eastern U.S. and a low-pressure system over the western U.S. folks all over the U.S. can then be expected to feel a westerly wind (wind moving from east to west) until the pressure in the east decreases and the pressure in the west increases to a point of equilibrium. think "entropy."
now transfer this train of thought to a zero-gravity environment. imagine a mass of air floating freely in space, free of any gravitational influences (or imagine the mass of air enclosed in a box that's floating freely in space, and just take the gravitational pull of the walls of the box to be negligible...either example is suitable). even if there is a temperature gradient in the mass of air, it will not convect b/c there is no source of gravity. i.e. the air molecules won't align themselves in layers of decreasing temperature/increasing density in the direction of some gravitational pull b/c we are in a hypothetical zero-gravity environment. any areas of high pressure (and thus denser air) though will spread out to fill in areas of lower pressure, causing air movement, and thus wind...at least up until the point that all the high-pressure and low-pressure areas have reached equilibrium and the pressure is constant throughout the entire mass of air.
so yes, wind can exist in a zero-gravity environment so long as there is a temperature gradient in the fluid.
...notice though that I'm holding to your definition of convection as the movement of air directly toward or away from a source of gravity, and it differs slightly from say, Darryl's definition. but if we define convection generally as buoyancy-driven flow (as Andy described it), then perhaps what i just described above is in fact convection. but either way, you can see how wind can occur in a gravity-free environment.
