[Physics] Why can’t we see clouds everywhere around us


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We see clouds at a particular height,and not everywhere near the ground.I am not really well versed in the concept of cloud,but I felt the clouds would be lighter by the way they look.So,they should have been at the bottom instead of being at the top.
I will be waiting to know the reason for clouds being only at the top and not anywhere else around us at the ground.

Best Answer

Clouds happen when there is more water in the air than it can hold. This forces whatever the air can't hold to condense, which forms tiny droplets, which in aggregate make clouds or fog.

The question then becomes, why does the air have more water in it than it can hold only in some places. To answer that, we have to look at why different locations have more or less water in the air, and why the air can hold more or less water in different locations.

That air in different locations has different amounts of water in it should be obvious. Air downwind of a warm lake, for example, can be expected to contain significant evaporation from that lake. Air in the desert, on the other hand, can be expected to contain little water since there is so little available.

As for how much water the air can hold, this is a function of temperature and pressure. Higher pressure (more air molecules in the same volume) can hold more water molecules. Warmer air can also hold more water. These are the two main reasons clouds are usually above us. The air is both colder and at lower pressure as you go higher.

Local geography and wind patterns can be a major influence. When moist air is blown accross a mountain range, it is forced to higher altitudes where its pressure and temperature will decrease. If the original humidity was high enough, then this cooler and less dense air won't be able to hold all the water anymore. That causes some to condense out to form clouds. If the condesation is heavy enough, the tiny droplets merge to form heavier drops, which then fall as rain.

This is why the upwind side of mountain ranges are usually much wetter than the downwind side. This is also why you are much more likely to find a desert just downwind of a mountain range. The air is forced to dump some of its water on the way up the mountains, so is much dryer when it gets back down the other side.

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