Oceanic Segment III: The Eckman Spiral
Isn’t that the coolest name you ever heard??
The Eckman Spiral flows on logically from the Coriolis Effect. In the Southern Hemisphere, Coriolis dictates that things kinda want to go left. Vice versa in the north.
So if you are a volume of water, just kicking it on the surface of the ocean in the sunny northern tropics and a wind comes along and moves you, you go with the wind, but also go a little to the right, in accord with Coriolis. So if a wind comes along from the south (so pushing everything northish), you will end up going something like 45degress east of north (45degrees to the right of north) once Coriolis and the wind direction are both accounted for.
So much for the surface waters.
Now the waters just below the surface never see the wind themselves. But they feel it indirectly through the motion of the surface waters. The surface waters move the deeper waters as they themselves move. But instead of being a force moving north like the wind was, they are moving east-of-north. So the deeper waters have forces urging them east-of-north (the surface waters) and slightly to the right (Coriolis), so they move a little more easterly again than the surface waters.
This effect continues down the water column, with each consecutively deeper volume of water moving more easterly than the volume above it.
And once all the levels are added up and accounted for, the whole water body moves 90degrees to the right of the direction of the wind. So, because of the Eckman Spiral, a wind from the south makes water masses move straight east.
This has major consequences for other processes such as upwelling, that we shall discuss in the next oceanic concept.