1987 Edition

Pressure gradient

Reference work entry

A pressure gradient is the rate of change (gradient) of atmospheric (barometric) pressure with regard to horizontal distance at a given point in time. The value is usually expressed in mb per 100 mi.

The pressure gradient is a force (P) that acts in a direction from higher toward lower pressure. In the atmosphere the pressure gradient force is directed perpendicular to the isobaric surfaces. It can be divided into two components, one that points vertically upward (Pv) and one that is horizontal (PH). The vertical component is balanced by gravity and is very small. However, small deviations are very important in the cloud formation process.

The horizontal component can produce relatively large accelerations. The size of PHdepends on the rate of change of pressure in the horizontal direction. Where the isobars are close together, the horizontal pressure gradient force is large; where the isobars are far apart, it is weak. A large (steep) gradient produces strong winds. Weaker winds are...

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© Van Nostrand Reinhold 1987

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