Curious Coriolis
Because of the spherical shape of the earth, the rate of rotation at a given point on the its surface depends on the latitude of the point. At the equator, the speed of travel is about 1,670 km/h, and at the poles 0 km/h. In Hamburg, the rate of rotational travel is only 980 kilometres per hour.
Now when a body moves northwards or southwards from the equator, it retains the rotational speed of the lower latitudes (aside from frictional losses). It will thus gain on the earth as the distance from the equator increases. Conversely, the earth will gain on a body approaching the equator from the North or South. This deflection is called the Coriolis force after the French physicist and engineer. In the northern hemisphere, the Coriolis force always deflects a travelling object to the right, and in the southern hemisphere to the left.
Strong, constant winds can quickly set water masses in motion, i.e. causing currents or drifts. Depending on wind speed and duration, a purely drift current carries water along down to varying depths: at wind force 4 down to 60 metres, in hurricanes down to a few hundred metres. However, once large masses of water get moving, various complex influences involving internal and external friction, such as deflections caused by the shape of the earth's surface, the form of the coastline and the Coriolis force resulting from the earth's rotation, act upon them.
When the wind blows across the surface of the water, the water particles offer frictional resistance to it. Added to this is the Coriolis force resulting from the planet's rotation. This turns the direction of wind-driven surface water currents 45 degrees to the right in the northern hemisphere and to the left in the southern hemisphere. At increasing depths the deflective force increases in strength while the speed of the currents decrease. Depending on the prevailing wind force, the water even flows against the direction of the wind at a certain depth.
Over the entire column of water down to this depth, the water is transported at a 90 degree angle to the direction of the wind (a phenomenon known as Ekman transport after the Danish marine physicist), to the right in the northern hemisphere and to the left south of the equator. Thus the water does not flow in the direction of the waves driven by the same wind, as may appear to be the case at first glance.