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pressure gradient[′presh·ər ‚grād·ē·ənt]
the change in atmospheric pressure per unit of distance along a normal toward an equal pressure surface (isobaric front) in the direction of a decrease in pressure.
Horizontal pressure gradients are commonly used in meteorology—that is, horizontal components of pressure gradients established at sea level or at another level. In this case, the isobaric normal toward an isobar is taken at a given level. Normally a horizontal pressure gradient is 1–3 millibars per 100 km, but in tropical cyclones the gradient sometimes reaches tens of millibars per 100 km (1 millibar = 100 newtons per sq m). The concept of a barometric grade is often used instead of the vertical pressure gradient.