Sea currents

The currents are classified according to various characteristics: by the forces causing them (genetic classification), by stability, by the depth in the water column, by the nature of the movement, and by their physicochemical properties.

Three groups of currents are distinguished:

• Gradient flows caused by horizontal hydrostatic pressure gradients arising when the isobaric surfaces are tilted with respect to isopotential (level) surfaces
  • Density caused by a horizontal density gradient
  • Compensation caused by sea ​​level tilt due to wind
  • Bar-gradient caused by uneven atmospheric pressure above the sea surface
  • Seiches arising from seiche oscillations of sea level
  • Stock or sewage resulting from the occurrence of excess water in any area of ​​the sea (as a result of the influx of mainland water, precipitation, melting ice )
• Wind currents
  • Drift caused only by the drag of the wind
  • Wind, caused by both the enticing effect of the wind, and the slope of the sea level and the change in water density caused by the wind
• Tidal currents caused by tides .
  • Breaking current

Tidal currents are the strongest, especially occurring offshore , in shallow water, in straits and estuaries .

In oceans and seas, currents are usually caused by the combined action of several forces. The currents that continue to exist after the end of the action of the forces that caused them are called inertial .

According to the variability, the currents are divided into periodic and non-periodic.

Periodic currents change with a certain period . Such currents include tidal currents.

Non-periodic flows are associated with temporary causes (for example, arise under the influence of a cyclone ).

Currents are distinguished, the velocities and directions of which change little during the season ( monsoon ) or per year ( trade winds ).

Currents that do not change in time are called steady currents , and those that change in time are called unsteady flows .

Wind currents are determined by the direction of the prevailing winds. These are always surface currents, they are formed under the combined influence of friction forces, turbulent viscosity, pressure gradient , Coriolis force . Among the strongest wind currents are the North and South Passat currents , the West Winds movement , etc. The theory of wind currents was developed by the Swede V. Ekman , Russian scientists V. B. Shtokman and N. S. Lineykin, American G. Stommel .

Density flows are determined by differences in the density of water. An example of a density current is the Gulf Stream , as well as the North Pacific Current.

• Thermohaline circulation
• Index cycle
• North Atlantic climate dynamics

• Evgenov N.I. Sea currents. - Ed. 2nd. - L .: Gidrometeoizdat , 1957 .-- 112 p. - 3000 copies.

• Sea currents - an article from the Great Soviet Encyclopedia .
• Sea currents // Brockhaus and Efron Encyclopedic Dictionary : in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.