Pressure Gradient Force

The atmosphere is not a uniform blanket of air. Pressure varies from place to place, and wherever it varies, the atmosphere tries to correct that imbalance. That attempt to correct itself is what we call a force — and it is the starting point for understanding why winds blow at all.

The force itself arises directly from differences in atmospheric pressure. Where two neighbouring regions have different pressures, the air between them experiences a push from the high-pressure side toward the low-pressure side. This push is the pressure gradient force. It is the fundamental driver of wind; without it, air would remain still.

To measure how strong this push is, we use the pressure gradient — the rate at which pressure changes with respect to distance. In other words, it tells us how quickly pressure falls off as we move from one point to another across a weather map.

The strength of the pressure gradient is read directly from the spacing of isobars, the lines joining points of equal pressure:

• Where isobars are close together, pressure changes rapidly over a short distance. The pressure gradient is strong, and the resulting force is large, producing faster winds. …