What is the ATMOSPHERE?
The atmosphere is the air that we breathe. It is also the wind and the wind chill and the wind speed that blows through our hair and the clouds that float in the sky. All the weather that takes place is part of the atmosphere. The atmosphere surrounds us at every moment, keeping us alive and warm. It is the part of the Earth system that we are most familiar with; so familiar that we often take it for granted. Without the atmosphere, we would perish within minutes.
There are a few important properties that have to do with the atmosphere. The first is temperature. That is simply how hot or cold the air is. During the day, the atmosphere is warmed by the sun, so the temperature goes up. At night, after the sun goes down, the atmosphere cools and the temperature drops.
Another property is called pressure. Pressure is the weight of the air over an area, and is usually given in pounds per square inch. The atmosphere is several kilometers thick. That means there is a lot of air above that is all pushing down on top of us. On the surface, there are small differences in pressure from place to place, and these differences are what lead to all the weather we experience.
When two neighboring regions are at different pressures, they are out of balance with each other. These pressure differentials cause pressure gradient forces which create winds and storms which try to restore the balance.
The atmosphere is the most dense near the surface because of gravity. As one goes higher, the air gets thinner and thinner. At an altitude of about ten kilometers, the atmosphere is only half as thick as at the surface. That's why air tanks are needed to climb Mt. Everest (nine kilometers high) and commercial airliners must be pressurized (flying at a height of about ten kilometers).
The last important property of the atmosphere is humidity. Humidity is a measure of how much water is in the atmosphere. When water evaporates from lakes and oceans, it turns into a gas and becomes part of the atmosphere. It is this water that sometimes condenses into clouds and becomes rain.
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