Ekman spiral
Vectors denoting the wind-induced velocity at different depths trace out a spiral about a line perpendicular to water surface
- Steady wind induces flow in lower layers at 90°, 180° or more to wind direction
- Current magnitude where flow is 180° to wind direction is usually ~4% of surface current
Definitions: (1) wind ‘penetrates’ to depth where flow is 180° to wind direction; (2) water above this depth of penetration is Ekman layer
Wind speed, water viscosity, & magnitude of Coriolis effect all affect depth to wind penetrates
Generally wind penetrates to greater depths at low latitudes (except right at equator)