- Trade winds set tropical water into west- ward motion --> equatorial currents
- Deflection by Coriolis Effect + reflection at continents --> western boundary currents = warm water currents
- West Wind Zone (20°-60°) --> create eastern boundary currents = cold water currents
- Western boundary currents ca. 10x faster than eastern boundary currents
- Eastern and western boundary currents enclose subtropical gyre
Wind-driven Currents: Ekman Spiral & Transport
- Fridjof Nansen (Fram) observed that arctic sea ice moved 20-40º to the right of wind direction. He passed his observations to Wilfrid Ekman
- Due to Coriolis effect surface water moves 45º to wind direction
- Dynamic energy is passed to deeper water layers
-
Energy
is dissipated due to friction --> depth at which current speed = 0:
Ekman depth - Coriolis force causes gradual deflection to the right (northern hemisphere) while passing energy further into deeper layers: Ekman spiral
- Net water transport over Ekman depth is 90º to wind direction
