Counterflow

Countercurrent - a current directed against the prevailing winds in a given area or against the movement of the main stable currents. It is customary to distinguish (because they have different mechanics) surface, subsurface and deep countercurrents.

The best-known are the trade wind surface counterflows , described as far back as the 19th century, which are caused by the transverse unevenness of the trade winds and directly depend on their intensity.

The trade winds (and trade winds ) are also responsible for the subsurface equatorial countercurrents of the Cromwell Current in the Pacific and the Lomonosov Current in the Atlantic Oceans .

Subsurface backflows are caused by a constant pressure gradient created by the main current, and therefore are much more stable. With the appearance of inhomogeneities or weakening of the winds, subsurface counterflows can “emerge” to the surface and be observed as surface counterflows.

Among the most powerful surface-subsurface countercurrents is the Peruvian-Chilean countercurrent ( Gunther current ). It is directed south along the west coast of South America between the northward Peruvian oceanic and Peruvian coastal currents (see Peruvian Current (Humboldt Current) ). A similar, but weaker countercurrent is observed on the western coast of Africa (in the region of Angola and Namibia ).

The most striking example of deep counterflow can be considered the deep counterflow under the Gulf Stream , which moves south at a depth of two to five kilometers at a speed of up to 20 cm / sec. ^{[1] [2]}

Bottom counterflows are also sometimes distinguished, which can be observed in the straits connecting the basins with sharply differing density, temperature and / or salinity of the water. For example, in the Strait of Gibraltar or in the Bosphorus . Moreover, the surface flow in these cases is directed to a pool of higher density, and the bottom flow to a pool with a lower density.