Complete collection of detailed information of seawater movement
Mbth: the moving factors of the ocean: the effect of sea breeze and the change of air pressure. Features: Regular and periodic main motion forms: waves, tides and ocean currents, waves, tides, ocean currents, meanings, ocean currents' causes, wind currents, density currents, compensation current, others, ocean currents' distribution. Due to the influence of geographical environment, the fluctuation of seawater is influenced by sea breeze and air pressure changes, prompting it to leave its original equilibrium position and move upward, downward, forward and backward. This formed waves at sea. Wave is a kind of regular periodic fluctuation. When the waves rush to the shore, the up-and-down movement of the lower water is hindered because the depth of the sea is getting shallower and shallower. Due to the inertia of objects, the waves of seawater are layered and more and more, and each wave is higher than the other. At the same time, as the water depth becomes shallower, the movement resistance of the lower water is getting bigger and bigger, so that in the end, its movement speed is slower than that of the upper water, and due to inertia, the highest part of the wave falls forward and falls to the beach, becoming splashing water. Tide Because the moon is closer to the earth than the sun, the tidal force ratio of the moon and the sun is 1 1: 5. For the ocean, the moon tide is more important than the sun tide. The driving forces of earth tides, ocean tides and atmospheric tides are all caused by the different gravitational forces of the sun and the moon on various parts of the earth, and they influence each other. The elastic-plastic tidal deformation of the ocean bottom crust will cause corresponding tides, that is, tides have tidal effects; The migration of seawater quality caused by tidal waves changes the load borne by the crust and makes it bend again. The air tide is above the sea tide, which acts on the sea surface and causes additional vibration, making the change of the sea tide more complicated. As a complete tidal science, its research object should be solid tide, ocean tide and atmospheric tide as a unified whole. However, because the tide phenomenon is very obvious and closely related to people's life, economic activities, transportation and so on, it is customary to interpret the word tide as ocean tide in a narrow sense. Due to the tidal force of the sun and the moon, the lithosphere, hydrosphere and atmosphere of the earth have periodic movements and changes respectively. The elastic-plastic deformation of the solid earth caused by the tidal force of the sun and the moon is called solid tide, which is referred to as solid tide or ground tide for short. The periodic rise and fall, fluctuation and advance and retreat of the sea surface caused by the tidal force of the sun and the moon are called ocean tides, referred to as ocean tides for short; Periodic changes of atmospheric elements (such as pressure field, atmospheric wind field, earth's magnetic field, etc.) (such as 8 12, 24 hours). ) caused by the tide is called the atmospheric tides, referred to as the tide. Among them, the atmospheric tide caused by the sun is called the solar tide, and the lunar tide is called the lunar tide. Ocean current, also known as ocean current, is a large-scale flow of seawater along a certain path in addition to tidal movement caused by tidal force. The factors that cause ocean current movement can be wind or uneven distribution of seawater density caused by hot salt effect. The former represents the wind stress acting on the sea surface, and the latter represents the horizontal pressure gradient force in the sea water. Coupled with the geostrophic bias, seawater flows both horizontally and vertically. Due to the obstruction and friction between the coast and the seabed, the current performance near the coast and the seabed is very different from that in the open ocean. Hot salt effects such as freezing, melting ice, precipitation and evaporation in the ocean cause uneven distribution of seawater density in a large area of the sea surface, which can generate high-density seawater on the surface of polar and high-latitude parts of the sea and sink to the deep sea and seabed. Under the action of horizontal pressure gradient force, it flows horizontally, and it can flow upward through the bottom of middle water and then to the surface. This is the hot salt cycle in the ocean. The wind drift on the ocean surface constitutes the wind-driven circulation on the ocean surface. Among them, the northern equatorial current and the southern equatorial current at low latitude and middle latitude are blocked by the coast at the western boundary of the ocean, and their mainstream turns to the north and south respectively. Due to the variation of Coriolis parameters with latitude (β effect) and horizontal turbulent friction, a current with stronger flow direction to the west, narrower flow amplitude and higher velocity is formed. Half of the heat transported from the equatorial region to the high latitudes of the earth every year is transported by the westward dense current at the western boundary of the ocean. In the northern hemisphere, the hot salt circulation entering the upper ocean is in the same direction as the westward strengthening current of the ocean, which increases the velocity; In the southern hemisphere, due to the opposite direction and slow flow rate, the ocean circulation is not obviously strengthened westward. The surface layer with a depth of less than 200-300 meters in the ocean is the wind drift layer. The resultant force of wind stress and horizontal turbulence stress acting on the sea surface by planetary wind system is balanced with geostrophic bias, and then wind drift occurs. The magnitude and direction of wind force in planetary wind system change with latitude, which leads to the convergence and divergence of sea surface water. On the one hand, it redistributes the density of seawater and produces a horizontal pressure gradient force. When it is balanced with the geostrophic bias force, a horizontal geostrophic flow is formed in a fairly thick horizontal layer. On the other hand, at the bottom of the wind drift layer in the equatorial region, seawater flows upward from subsurface water or falls into subsurface water, forming ascending and descending airflow in the equatorial region. In the mid-latitude and high-latitude areas of the southern hemisphere, due to the lack of continental coast, the wind-driven circulation on the ocean surface forms the Antarctic circumpolar current that flows continuously around the Antarctic continent. In the eastern ocean and coastal waters, when the wind blows evenly along the coast for a long time, on the one hand, the wind drifts, and the seawater converges and diverges horizontally, resulting in upwelling and downwelling; On the other hand, due to the accumulation and loss of coastal seawater, the sea surface tilts, and the horizontal pressure gradient force produces coastal current, forming coastal wave current. The ocean current that strengthens to the west flows northward in the northern hemisphere (southward in the southern hemisphere) and then turns eastward. When it reaches a certain area, the current begins to be unstable, and the axis of the current bends in waves near its average position, resulting in the phenomenon of current bending (or winding). Finally, a circulation is formed, leaving the mother body, resulting in a cold current ring composed of cold water from the continental shelf and a warm current ring composed of warm water from the ocean interior. This is a mesoscale vortex with mesoscale. In addition, in other parts of the ocean, due to the instability of ocean currents, other kinds of mesoscale vortices can also be formed. These mesoscale vortices concentrate a large part of the energy in the ocean, forming various weather vortices superimposed on the average circulation field of marine climate, which makes the ocean circulation more complicated. In the continental shelf or shallow sea of the ocean, due to the obvious friction between the coast and the seabed and the particularly strong tidal current, quite complex shallow sea currents such as continental shelf circulation, shallow sea circulation and strait current are formed. Current can be divided into cold current and warm current according to whether its water temperature is lower or higher than that of the sea area it flows through. The former comes from low water temperature, while the latter comes from high water temperature. The horizontal velocity of the surface ocean current varies from a few centimeters per second to 300 centimeters per second, while the horizontal velocity of the deep ocean current is below 10 centimeter per second. The vertical speed is very small, from a few centimeters per day to dozens of centimeters per hour. Ocean currents flow in the direction of flow, which is the opposite of the definition of wind direction. Meaningful ocean currents have influences and constraints on many physical, chemical, biological and geological processes in the ocean, as well as the formation and changes of climate and weather over the ocean. Therefore, understanding and mastering the laws of ocean currents, large-scale air-sea interaction and long-term climate change is of great significance to fisheries, shipping, sewage discharge and military affairs. According to the causes of ocean currents, the causes of ocean currents can be divided into three categories: airflow, atmospheric movement and near-surface wind zone, which are the main driving forces of ocean current movement. The prevailing wind blows the sea surface and pushes the sea water to drift with the wind, so that the upper sea water drives the lower sea water to form a large-scale ocean current, which is called wind current. For example, under the action of the northeast trade wind, the northern equatorial warm current A flows from northeast to southwest, and is influenced by geostrophic deflection in the process of horizontal movement, and finally deflects into an equatorial warm current flowing from east to west. Density current is called density current because the temperature and salinity of seawater in different sea areas are different, resulting in different seawater densities and different seawater flows. Density current is not only distributed in the Strait of Gibraltar, but also in the Red Sea and Indian Ocean, Red Sea and Mediterranean Sea, Baltic Sea and North Sea, Mediterranean Sea and Black Sea. The surface water of the Indian Ocean flows to the Red Sea, and the bottom water of the Red Sea flows to the Indian Ocean. Distribution law of density current: in the strait between the closed sea area and the open ocean, the distribution of density current is generally obvious. The Strait of Gibraltar, which connects the Mediterranean Sea and the Atlantic Ocean, is a typical example of density current. The Mediterranean region has a Mediterranean climate, with hot and dry summers and mild and humid winters. The Mediterranean Sea has large evaporation and high salinity, while the Atlantic Ocean has high density, low water surface, low salinity, low density and high water surface. Therefore, the water level of the Atlantic Ocean is higher than that of the Mediterranean Sea, and the surface seawater of the Atlantic Ocean will flow into the Mediterranean Sea through the Strait of Gibraltar, while the bottom seawater of the Mediterranean Sea will flow into the Atlantic Ocean from the bottom of the Strait. In World War II, German submarines used this principle to enter the Gibraltar Strait, shut down their engines, avoided the monitoring of the British army, and went around behind the British army, thus successfully attacking the British army. The ocean current formed by the difference of wind force and density in the compensation current reduces the seawater flowing out of the sea area. Due to the requirement of seawater continuity and compensation for losses, the seawater in the adjacent waters will flow and replenish, and the ocean current thus formed is called compensation current. The formation of compensation current is closely related to wind current and density current. It can be divided into horizontal compensation current and vertical compensation current. The latter is also called upward flow and downward flow, including upward flow and downward flow. The vertical compensation current mainly occurs in coastal areas. Near the coast, seawater moves under the action of wind and is influenced by offshore wind or coastal wind. Affected by offshore winds. With the sea breeze blowing, the surface seawater moves offshore, which leads to the seawater velocity in the adjacent sea area to compensate for the shortage of seawater, and the lower seawater also rises to the sea surface, and the seawater coming to compensation current forms an upwelling (cold current on both sides of the mainland in the low latitude trade wind area). When the surface seawater is blocked by the coast or island, the seawater gathers and splits in the horizontal direction, resulting in downward flow in the vertical direction. Impact: Upflow can bring nutrients from the bottom to the surface, make plankton grow in large numbers and provide bait for fish. Therefore, the upwelling waters often form important fishing grounds, such as the Peruvian fishing grounds, which benefit from the Peruvian cold current (rising to compensation current). There are other sea areas in the world that also have rising compensation current distribution, such as California cold current, Benguela cold current and Canary cold current. The formation of other ocean currents is not only affected by the above factors, but also by the land shape and geostrophic deviation, which will force the ocean currents to change their flow direction during the movement. The formation of ocean current is the result of the comprehensive action of many factors, which makes the distribution of ocean current very complicated, but it also has certain laws. Ocean current distribution Although the distribution and direction of ocean current are complicated, there are still laws to follow. (1) A low-latitude circulation is formed between the equator and 40-60 degrees north and south latitude, and its flow direction is clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. The western part of each circulation is warm current, and the eastern part is cold current. (2) A high latitude circulation is formed north of 40 or 60 north latitude. Its circulation direction is counterclockwise, with cold current in the west and warm current in the east. (3) The North Indian Ocean north of the equator belongs to monsoon current because it is located south of the Tropic of Cancer. In winter, the northeast monsoon blows, the surface seawater flows westward, and the ocean current flows counterclockwise; In summer, the southwest monsoon blows, the surface seawater flows eastward and the ocean current flows clockwise. (4) The east-west ocean currents are all warm currents except west wind drift in the southern hemisphere. Ocean current has a great influence on the coastal climate of the mainland, and the area where the cold current passes has the function of cooling and dehumidifying the climate; Warm current has the function of warming and humidifying the climate along the way. The influence of geographical environment summarizes the global ocean circulation, which is of great significance to the heat transport and exchange in high and low latitudes and the regulation of global heat distribution. Ocean currents have an impact on coastal climate, marine life distribution, fishery production, navigation, etc., and have an important contribution to the process of human civilization and social life. Impact on Climate Warm current plays a role in warming and humidifying the climate flowing through coastal areas. For example, the formation of maritime climate in western Europe is influenced by the North Atlantic warm current. The cold current plays a role in cooling and dehumidifying the climate flowing through the coastal areas. For example, the coastal cold current has a certain effect on the formation of desert environment on the west coast of Australia and the Pacific coast of Peru. If the ocean current is abnormal, the global atmospheric circulation will also be abnormal, which will affect the climate. Such as: El Nino phenomenon. It shows that El Nino is a global phenomenon. Generally speaking, in the East Pacific, under the influence of ocean currents and trade winds, the seawater in the eastern sea flows northwest with the warm current of the South Equator, and the eastern sea provides upwelling compensation, which is characterized by low water temperature in the eastern sea and high water temperature in the west. When El Nino occurred, the upwelling of cold water stopped and disappeared along the coast of Peru due to the rising temperature on the east coast of the ocean and the coast of Peru, which made the atmospheric circulation abnormal and the precipitation changed. For example, El Nino in 1982- 1983 caused a sudden increase in precipitation and flooding in Peru along the equatorial eastern Pacific Ocean. The persistent drought in Australia and Indonesia on the west side of the Pacific Ocean has caused forest fires, especially in Africa. Our country is also affected by it. For example, in 1998, one of the natural causes of the catastrophic floods in the Yangtze River Basin in China was the impact of El Niñ o. As for El Nino, we haven't fully grasped its activity law, and scientists are actively studying it. Therefore, we should attach great importance to international cooperation and establish a global marine and atmospheric monitoring network to minimize losses. The influence of ocean currents on the distribution of marine life is mainly the formation of fishing grounds. The four major fishing grounds in the world can be divided into two categories: one is the confluence of cold and warm currents, and the other is the rising place of compensation current (Peruvian fishing ground). Because the confluence of cold and warm air currents and upwelling can bring nutrients to the ocean surface. At the intersection of cold current and warm current, the sea water is disturbed, causing the sea water to churn up and down, so it brings rich nutrients from the lower layer to the surface layer, prompting plankton to multiply in large numbers, and all kinds of fish gather here to feed, forming a fishing ground. The three world-famous fishing grounds are all located in the sea area where cold current and warm current meet. They are Hokkaido Fishing Ground (Japan), Beihai Fishing Ground (UK) and Newfoundland Fishing Ground (Canada). Impact on marine pollution After pollutants from land enter the ocean, ocean currents can bring pollutants from offshore to other sea areas, thus expanding the scope of pollution. However, with the movement of ocean currents, pollutants will spread to other sea areas and speed up the purification. For example, the recent oil spill from an oil tanker in Spanish waters has seriously polluted 350 kilometers of coast and caused serious damage to local fishery production and ecological environment. However, the rapid flow of fuel to other sea areas has also relatively slowed down the pollution in this sea area. The impact on navigation is just as we usually go faster with the wind than against the wind. Sailing generally chooses coastal areas with smooth sailing.