Hi TinselKoala,

I have a question which you perhaps could kindly answer:

before rain fall, water vapor condenses and same amount energy which was used to evaporate water is released, isn't it ? Why we need Sun for this process ?

Thanks,
Vasik

The water is transported to a higher elevation by air movement. It needs an energy source for this to happen. As it happens parcels of air are heated and are transported to higher elevation because they are less dense than the surrounding air and rise due to buoyancy.

This transport of air carries  water vapour to higher elevation where it eventually condenses and falls as rain. As you suggest the condensation of air does release heat at altitude but this actually counteracts the thermal gradient that causes the air to rise in the first place.

The heating and heat release don't necessarily occur in the same location. We feel that effect as wind.

 

Actually only partially true. Building cumulus clouds and thunderstorms and other heavy weather are indeed driven by the reinforced convection caused by the release of the latent heat of evaporation when the water vapor condenses. It all depends on the local "adiabatic lapse rate" which is the rate at which the air cools off with increasing altitude due to the change in pressure. If the actual surrounding air cools at a greater rate than the adiabatic lapse rate, then a rising parcel of air, which cools naturally at that rate as its pressure drops, becomes increasingly warmer than the surrounding air as it rises. When the parcel cools to the point at which condensation begins, the release of energy causes the parcel to be that much warmer than the air around it so its rise actually can accelerate.

Good luck doing it without losses that need to be made up from outside, and good luck taking work out of the system... which will also need to be made up by supplying energy from outside.

Well, I think it can be done...