If hot air rises, then why are many low-lying areas so hot?
In: Earth Science
It has more to do with the wind. Low lying areas are surrounded by areas of higher ground. Those higher areas act as a buffer and shield for the wind. Without any wind the heat from the sun doesn’t get pushed around. It just builds and builds and builds.
Hot air rises, but the atmosphere cools the higher up you go. The reason for this apparent contradiction is that pressure decreases the higher you go, which allows the air to expand. And when gases expand, they cool down.
The hottest places on Earth are the result of warm, moist air rising, rain falling on high mountains, and then the resulting dry air falling on the other side. Moist air heats and cools by a smaller amount as it rises and falls than dry air does, so what happens in those settings is you get something like:
30 C moist air -> rises up and becomes 10 C moist air (loses 20 C as it rises) -> rain falls -> now is 10 C *dry* air -> descends the other side of the hill -> heats up by more than it cooled down before and hits the valley as 40 C dry air (gains 30 C as it descends).
It isn’t the air which is heating up the area, it is the ground which is heating up the air.
The hot air rises, but the ground is still hotter than the surrounding air.
Think of it this way. Have you seen a poofy jacket? The air in the jacket holds in the heat. The poofier the jacket, the warmer it is, just like the more air above you the warmer the air can become. It can hold more energy. Air higher up isn’t as dense, so it can’t hold as much heat.
1. The rate at which the sun heats up the ground is faster than the rate at which the rising air carries that heat away.
2. Low-lying areas are usually close to the sea, and the heat trapped in the sea also helps to heat up the coastline
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