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Atmospheric pressure is caused by
the weight of the air above. At sea level on Earth, on average,
atmospheric pressure is about 15 pounds of weight distributed over every
square inch of surface area. This means that a column of air an
inch across and stretching upward to the "top" of the
atmosphere only weighs 15 pounds.
Differences in surface air
pressure from one region to another are caused by solar heating.
As the Sun's energy heats up Earth's surface, the atmosphere above also
heats up, causing the air to expand and become less dense. Less
dense air weighs less than a similar volume of denser air, and so
atmospheric pressure is less. It is differences in atmospheric
pressure between one region and a neighboring region that drive
winds.
Air at lower pressure is less
capable of containing water vapor (water in its gaseous state), and so
low pressure regions are more prone to the formation of clouds by
condensation, especially if the air is cooled and becomes even less
capable of holding water vapor. Storm systems are typically
associated with low pressure zones. |
