Inverse Barometer Effect

The inverse barometer effect is the response of sea level to changes in atmospheric pressure: water rises under low pressure and falls under high pressure. The standard rule is about 1 cm of sea-level change per 1 hPa (1 millibar) of pressure change, an isostatic balance of the static water column. The ocean does not respond instantly or pointwise; it adjusts to the pressure averaged over a wide area. Pressure alone seldom shifts level beyond about 30 cm, but it accompanies the wind of a depression, so the combined surge is often larger. Correcting for it isolates the astronomical tide from meteorological residual.