In oceanography, the turning of the current vector that arises from stratified geostrophic flow when density is conserved following a parcel (as is approximately the case in the oceanic thermocline). If θ is the angle of the current, U is its magnitude, f is the Coriolis parameter, g is the gravitational acceleration, and w is the vertical velocity, then ∂θ/∂z = −(gw/fU2)(∂/∂z), so that moving upward in the water column, currents will spiral clockwise in upwelling zones, and counterclockwise in downwelling zones.