what are pressure gradients?

Answer 1

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 in 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.

Answer 2

A gradient of any kind is simply a change in something over some basis. A gradient and a slope are essentially the same thing.

A pressure gradient is just a change in pressure over some change in something like temperature or distance. On a weather map, you may see some squiggly lines called isobars. Literally, iso means same and bar means pressure. Thus, a single line represents a location over ground where the pressure is the same value.

The gradient in the case of isobars is the difference in pressure between the different isobars. For example, if one isobar is at p = 15 psi and another is at P = 16 psi, the pressure gradient is P - p = 1 psi per isobar. It could also be indicated as P - p = 1 psi per mile, for example, if we measure how far the isobars are apart on the ground.

When the isobars are tightly bunched together, the pressure gradient is steep because there is a lot of pressure change over a short distance on the ground. These sharp pressure changes typically invoke heavy winds because the air cascades down the steep gradient like water tumbles over a falls.