Vertical Velocity (w)

Vertical velocity w is the component of fluid velocity perpendicular to the horizontal plane, the rate of change of a parcel’s depth. In the large-scale ocean it is small, of order meters per day or 10^-5 to 10^-4 meters per second, far below horizontal speeds, because strong stratification suppresses vertical motion. It is rarely measured directly; instead it is inferred from horizontal divergence through the continuity equation grad dot v = 0, from Ekman pumping at the mixed-layer base, or from the omega equation in QG theory. Vertical velocity controls upwelling, subduction, and the vertical supply of nutrients.