In the Ekman Spiral, the surface layer drifts at what angle to the wind in the Northern Hemisphere?

• A. 90 degrees
• B. 45 degrees
• C. 0 degrees
• D. 30 degrees

Answer: (B)

In the Ekman spiral, the surface current is deflected to the right of the wind in the Northern Hemisphere because the Coriolis effect acts on moving water and friction couples the surface layer to deeper layers. The simplest, idealized model of the Ekman layer shows that the balance between wind forcing, Coriolis deflection, and viscous interaction across the depth causes the surface velocity to point halfway between the wind direction and the rightward direction. That puts the surface current about 45 degrees to the wind. The whole layer then rotates with depth, forming the spiral, and the total water transport ends up at 90 degrees to the wind. So, the surface drift is roughly 45 degrees to the wind in the Northern Hemisphere. (Keep in mind this is an idealized result; real conditions can shift the angle somewhat.)