Atmospheric Pressure

Atmospheric pressure is the force exerted by the weight of the atmosphere. It is primarily affected by the temperature of the air. When it is warm, the air expands and becomes lighter. Light air rises and exerts lesser pressure on the surface of Earth. When it is cold, the air turns heavier and sinks. Heavier air pushes the lighter air upward and the movement causes the formation of wind, or moving air.

Meteorologists use an instrument called barometer to measure atmospheric pressure. There are two commonly used kinds of barometers: mercury and aneroid.

A mercury barometer is a glass tube about 91 cm long and filled with mercury. The level of the mercury in the tube indicates the atmospheric pressure in a place. The mercury rises when atmospheric pressure increases and goes down when atmospheric pressure decreases.

The aneroid barometer is an air-tight metal instrument that is very sensitive to changes in atmospheric pressure. Unlike the other type, it does not use mercury.