Pressure gradient

In atmospheric sciences (meteorology, climatology and related fields), the pressure gradient (typically of air, more generally of any fluid) is a physical quantity that describes which direction and at what rate the pressure changes the most rapidly around a particular location. The pressure gradient is a dimensional quantity expressed in units of pressure per unit length, or Pa/m

Mathematically, it is obtained by applying the del operator to a pressure function of position. The negative gradient of pressure is known as the force density.

In the Petroleum Geology and Petrochemical sciences pertaining to oil wells, and more specifically within Hydrostatic Pressure, pressure gradients refer to the gradient of vertical pressure in a column of fluid within a wellbore generally expressed in psi/ft. this column of fluid is subject to the compound pressure gradient of the overlying fluids. The path and geometry of the column is totally irrelevant, only the vertical depth of the column has any relevance on the vertical pressure of any point within its column and the pressure gradient for any given true vertical depth.

Strictly speaking, the concept of pressure gradient is a local characterisation of the air (more generally of the fluid under investigation). The pressure gradient is defined only at those spatial scales at which pressure (more generally fluid dynamics) itself is defined.

Within planetary atmospheres (including the Earth's), the pressure gradient is a vector pointing roughly downwards, because the pressure changes most rapidly vertically, increasing downwards, see vertical pressure variation. The value of the strength (or norm) of the pressure gradient in the troposphere is typically of the order 9 Pa/m (or 90 hPa/km).

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