Ekmanspiral : A logarithmic spiral (when projected on a horizontal plane) formed by the heads of current velocity vectors at increasing depths. The current vectors become progressively smaller with depth. They spiral to the right (looking in the direction of flow) in the Northern Hemisphere and to the left in the Southern with increasing depth. Theoretically, in deep water, the surface current vector sets 45° and the total mass transport sets 90° from the direction toward which the wind is blowing. Flow opposite to the surface current occurs at the so-called 'depth of frictional resistance'. The phenomenon occurs in wind drift currents in which only the Coriolis and frictional forces are significant. Named for Vagn Walfrid Ekman who, assuming a constant eddy viscosity, steady wind stress, and unlimited water depth and extent, derived the effect in 1905.