Abstract
Abstract. We re-visit Ekman's (1905) classic problem of wind-stress-induced ocean currents to help interpret observed deviations from Ekman's theory, in particular from the predicted surface current deflection of 45∘. While previous studies have shown that such deviations can be explained by a vertical eddy viscosity varying with depth, as opposed to the constant profile taken by Ekman, analytical progress has been impeded by the difficulty in solving Ekman's equation. Herein, we present a solution for piecewise-constant eddy viscosity which enables a comprehensive understanding of how the surface deflection angle depends on the vertical profile of eddy viscosity. For two layers, the dimensionless problem depends only on the depth of the upper layer and the ratio of layer viscosities. A single diagram then allows one to understand the dependence of the deflection angle on these two parameters.
Highlights
The motion of the near-surface ocean layer is a superposition of waves, wind-driven currents and geostrophic flows
Ekman dynamics is due to the balance between Coriolis and the frictional forces generated by the wind stress
The surface current is deflected to the right and left of the prevailing wind direction in the Northern Hemisphere and Southern Hemisphere, respectively
Summary
The motion of the near-surface ocean layer is a superposition of waves, wind-driven currents and geostrophic flows. The basic theory of wind-driven surface currents in the ocean, away from the Equator, is due to Ekman (1905) and constitutes a cornerstone of oceanography (see Vallis, 2017). Ekman dynamics is due to the balance between Coriolis and the frictional forces generated by the wind stress. Consistent with observations of steady wind-driven ocean currents, are the following: i. The surface current is deflected to the right and left of the prevailing wind direction in the Northern Hemisphere and Southern Hemisphere, respectively. With increasing depth in the boundary layer, the current speed is reduced, and the direction rotates farther away from the wind direction following a spiral
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
