Ekman, Vagn Walfrid

(1874–1954) Swedish oceanographer: explained the variation in direction of ocean currents with depth.

After graduation, Ekman worked at the International Laboratory for Oceanographic Research in Oslo for several years before returning to Sweden in 1908. He was appointed professor of mathematical physics at Lund in 1910. In the 1890s the Norwegian Arctic explorer had noted that the path of drifting sea ice did not follow the prevailing wind direction, but deviated about 45° to the right. In 1905 Ekman was able to explain this as an effect of the Coriolis force caused by the Earth’s rotation. He went on to describe the general motion of near-surface water as the result of the interaction between surface wind force, the Coriolis force and frictional effects between different water layers. Ekman flow thus accounts for situations in which near-surface water moves in the opposite direction to that at the surface, with the net water transport at right angles to the wind direction. The resulting variation of water velocity with depth is known as the Ekman spiral. An analogous situation exists in atmospheric flow.