Atmospheric Pressure

Atmospheric pressure is the force per unit area exerted by the weight of the air column above a point, measured with a barometer and reported in hectopascals (1 hPa = 1 mbar). Standard sea-level pressure is 1013.25 hPa. It falls roughly exponentially with height, near 12 hPa per 100 m in the lower troposphere, and varies horizontally by tens of hectopascals between highs and lows. The horizontal pressure gradient drives the wind, balanced by the Coriolis force in the free atmosphere. Tropical cyclone centers can fall below 900 hPa; mid-latitude highs exceed 1040 hPa.