1. Marine winds and currents?
The warm north and south equatorial currents in the trade wind belt. The western drifts of the Western Belt are separated by land in the Northern Hemisphere and are called the North Atlantic Warm Current and the North Pacific Warm Current. In the southern hemisphere, they go around Antarctica and connect the three oceans (Indian Ocean, Pacific Ocean, Pacific Ocean). and Atlantic Ocean). Westerly drifts in the Southern Hemisphere are cold currents. Northern Indian Ocean monsoon currents (the northeast wind blows counterclockwise in winter and the southwest wind blows clockwise in summer. )
Compensating currents
For example, the cold water of the Indian Ocean. The Arctic Sea is flowing south, which will cause the warm current to shift north to compensate. Another example is that near 60°-64°S in the Southern Ocean,due to the existence of the Antarctic Divergence Zone, surface waters flow here and deep waters rise here. The amount of rising water reaches 60×106 m3/s. which represents the largest volume in the world's oceans. One of the areas with the greatest compensation effect.
3. Density flow
For example, the Mediterranean Sea has high evaporation, high salinity, and high density, while the density of adjacent Atlantic seawater is low, so a density current occurs form and the water of the Mediterranean Sea flows from the bottom of the strait and enters the Atlantic Ocean, and the surface waters of the Atlantic Ocean flow into the Mediterranean Sea through the Strait of Gibraltar.
Detailed information
1. Causes of Wind and Ocean Currents
Ocean currents are caused by shear stress generated by prevailing currents. the continuous action of the wind on the surface of the sea. Under the action of wind shear stress and turbulent mixing, the accumulation and density of sea water are redistributed, resulting in horizontal pressure gradient force and turbulent friction. After equilibrium with the Coriolis force, wind currents are generated.
When the turbulent mixing is strong enough to even out the density distribution, no horizontal pressure gradient force is generated and only the vertical turbulent frictional force of the seawater and the force of Coriolis are balanced, the wind current at this time is called "drift".
Under the action of the Coriolis force, the direction of surface waters drifting in the infinite deep sea always deviates from the wind direction by 45°, to the right in the hemisphere north and to the left in the southern hemisphere. hemisphere. This bias increases with depth and the flow velocity decreases with pdepth. The depth reached at which the flow velocity is only 4% of the surface flow velocity is called "Ekman depth".
2. Reasons for the formation of compensation currents
The main reason for the formation of compensation currents is that ocean currents formed by differences in wind and density cause a shortage of sea water in the area of seawater flow, such as updrafts and downdrafts. In the northern hemisphere, when the wind blows parallel to the coast (located to the left of the wind direction) for a long period of time, wind drift caused by the wind moves the surface. water moves away from the coast (called a rip current) under the action of the geostrophic deflection force, causing lower seawater near the coast to rise, forming an upwelling.
A downwelling forms far from the coast; , which flows from the lower layer vers the coastline to compensate for the loss of seawater close to the coastline. A similar situation is occurring in the southern hemisphere.
There are upwellings evident in the marine areas of each ocean. Upwellings can bring to the surface a large amount of seawater nutrients (phosphates, nitrates, etc.) present in the deep sea, thus providing abundant food. upwelling sea areas with strong currents are mostly famous fishing grounds, such as the Peruvian fishing ground, one of the four famous fishing grounds in the world (formed under the influence of the Peruvian cold current;
The west coast of Peru, Under the continuous blowing of the southeast trade wind, the warm upper sea water flows westward offshore and the cold sea water from the Deep water rises. Rising cold sea water brings more nutrients, allowing plankton to bloom and form.)
3. Formation of density flowté
Factors that cause differences in density include temperature, dissolved solids content, and mixture content. For example, when hot waste water from a factory is discharged into a river. , a large temperature difference flow is formed, and fresh water Intersects with salt water to form a hyperpycnal flow of salt water, and the river transports sediment to form a hyperpycnal flow of muddy water, etc.
Due to differences in the intensity of solar radiation received by each sea area, the sea water temperature appears to be different, and the sea water temperature at low latitudes is higher. The volume of sea water increases. The density of sea water will decrease and the sea surface (isobaric surface) will increase. In another sea area, the sea water temperature is relatively low and the sea surface is lower. Under the action of a force of gradient of horizontal pressure, seawater will flow towards the sea area having a lower sea surface.
In addition, due to the difference in seawater salinity, the density of seawater will also be affected. The higher the salinity of the sea water, the density of the sea water will also increase (the sea level is lower). Differences in ocean temperature and salinity lead to differences in the density of seawater, causing the flow of ocean water to form density currents.
In fact, the flow of seawater on Earth is shaped by the interaction between the ocean and the atmospheric environment. The ocean carries thermal energy to the atmosphere, and the atmosphere carries kinetic energy to it. Sea water forms a certain regular movement pattern under the combined influence of many factors such as sea water temperature, salinity, continental topography andgeostrophic deviation. It is impossible to have simple wind currents or density currents.
Baidu-Density Encyclopedia. Flow
Baidu Encyclopedia-Compensation flow
Baidu Encyclopedia-Wind and sea current