What's the difference between cold wave and cold wave? What about ocean currents and atmospheric circulation?

The difference between cold wave and cold wave

Every winter, there are a lot of strong cold air going south, which causes a large-scale cooling in China. Many media in our country are used to calling it "cold current", which is incorrect. This phenomenon should be called "cold wave". So what is a "cold wave" and what is a "cold wave"? How to distinguish the two? Here's a detailed explanation:

Cold wave is a common disastrous weather in China, which occurs frequently and has a wide range of activities. A cold wave, as its name implies, is a surge of cold air like a tide. But not all cold air attacks are called cold waves. Generally, after cold air attacks a place, if the temperature in those places can drop by more than 10 degrees Celsius in one day (24 hours), and the lowest temperature in that day is below 5 degrees Celsius, we call this cold air a cold wave. However, due to the influence of geographical environment and climatic conditions, the cold wave standards are also different.

Causes of Cold Wave: The cold wave invading China mainly broke out in the Arctic, Siberia, Russian and Mongolian. Most of these areas are located in the Arctic. In winter, there is no sunshine for a long time, and there is snow and ice everywhere. The air mass staying in these areas is getting colder and drier, as if it were lying in a large natural freezer. When this cold air mass accumulates to a certain extent and the air pressure in the south increases to a much higher level, it is like a flood stored in the mountains. At the first opportunity, it floods to the south with lower air pressure, forming a cold wave.

The result of cold wave: In places hit by cold wave, the wind direction often changes rapidly, the wind speed increases, the air pressure suddenly rises, the temperature drops sharply, and there may be rain, snow and frost. The cold wave goes south, and windy and dusty weather often occurs in northwest, Inner Mongolia and North China. In the area north of Huaihe River, there is generally little rain and occasional snowfall. After crossing the Huaihe River, the chances of precipitation increase. Generally, there is a cold wave every 3-8 days in winter in China, but the relatively strong cold wave has an average of about 4 times a year. Generally, it occurs from the end of 10 to the end of 10 the following year, and cold waves also occur in late February in some years. When the cold wave moves south on a large scale, the warm air will also "retreat one after another", so the area it passes through will be affected by the warm air first, and the temperature will increase obviously. If the passing area is already under the control of the warm air mass, there will also be weather in which the temperature rises sharply under the continuous delivery of warm air before the cold wave. Because t? Oh? Do you teach me? /P & gt；

The route of cold wave invading China: The cold wave invading China is not always the same, depending on which part of the Arctic and Siberia has the highest cold air pressure and which part of China has the lowest air pressure. In addition, it is also influenced by the high mountains in China.

So what kind of phenomenon is the cold current? To know what a cold current is, we must first understand what an ocean current is. The water on the ocean surface flows slowly and regularly in a certain direction at a huge scale and relatively stable speed. This is the so-called ocean current, also called ocean current. Ocean currents can be divided into warm currents and cold currents according to their nature. Any flowing ocean current whose seawater temperature is higher than the sea area it passes through is called warm current, and generally the ocean current flowing from low latitude to high latitude belongs to warm current; Any flowing ocean current whose seawater temperature is lower than the passing sea area is called cold current. Generally, the ocean current flowing from high latitude to low latitude belongs to cold current. The east-west ocean current is generally warm, only west wind drift in the southern hemisphere, affected by the Antarctic continent and sea ice floes, has a low seawater temperature and belongs to the nature of cold current.

Influence of ocean current: The main influence of ocean current is that it has a great influence on the coastal climate of the mainland. The cold current will reduce the temperature and precipitation flowing through the sea and coastal areas. The sea areas and coastal areas where warm current flows are generally warmer than other sea areas at the same latitude, with moist air and abundant rainfall, which is beneficial to agricultural production.

The main causes of ocean currents are: the sea surface is blown by long-term stable wind direction; In addition, it is also related to the density of seawater, the height of sea surface, the deflection of the earth's rotation, the outline of land and the distribution of islands. Although the distribution and direction of ocean currents are very 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.

From the above analysis, it can be seen that cold wave belongs to a form of air (cold air) flow, while cold wave belongs to the category of ocean current (seawater) flow. So we say that cold wave and cold wave are two completely different concepts and cannot be confused.

(Source: Original Works)

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atmospheric circulation

Atmospheric circulation

The state of large-scale movement of the atmosphere. In a large area (such as Europe, Asia, hemisphere and the whole world), the average state of atmospheric movement in a long period (such as month, season, year and year) or the changing process of atmospheric movement in a certain period (such as one week and meiyu period) can be called atmospheric circulation.

Atmospheric circulation is an important mechanism to complete the transport and balance of angular momentum, heat and water vapor and the mutual transformation of various energies in the terrestrial-atmospheric system, and it is also an important result of the transport, balance and transformation of these physical quantities. Therefore, studying the characteristics, formation, maintenance, change and function of atmospheric circulation and mastering its evolution law are not only an indispensable part of human understanding of nature, but also conducive to improving and improving the accuracy of weather forecast, exploring global climate change and making more effective use of climate resources. Atmospheric circulation usually includes three parts: average zonal circulation, average horizontal circulation and average meridional circulation.

① Mean zonal circulation. Refers to the prevailing zonal airflow in the atmosphere, centering on the polar regions and rotating around them. This is the most basic state of atmospheric circulation. As far as the mean zonal circulation in the troposphere is concerned, the easterly winds prevail in low latitudes, which is called easterly winds (due to the rotation of the earth, most of the northern hemisphere is northeast trade winds, and most of the southern hemisphere is southeast trade winds, so it is also called trade winds); The westerly winds prevail in the middle and high latitudes, which are called westerly belts (its intensity increases with height and reaches the maximum near the tropopause, which is called westerly jet); There is also a shallow weak easterly wind in the polar region, which is called polar easterly wind.

② Average horizontal circulation. Refers to the wavy airflow prevailing on the horizontal plane in the middle and high latitudes (also known as the average trough ridge). Usually there are three waves in winter and four waves in summer in the northern hemisphere. The transition between the three waves and the four waves represents the seasonal change.

③ Average radial circulation. Refers to the motion state composed of meridional motion and vertical motion of the atmosphere on the north-south vertical section. Usually, there are three circles in the troposphere: the low latitude is positive circulation or direct circulation (the airflow rises at the equator, goes north at high altitude, sinks at middle and low latitudes, and goes south at low altitude), also called Hadley circulation; Mid-latitude is anti-circulation or indirect circulation (low latitude airflow sinks, low altitude goes north, high latitude rises, high altitude goes south), also called Ferrer circulation; The polar region is a weak positive circulation (polar sinking, low altitude to the south, high latitude rising, high altitude to the north).

The concept of ocean current

Ocean currents are also called ocean currents. It is different from the tidal current that periodically changes its own velocity and direction, but has a relatively stable seawater flow direction. Ocean currents can be shallow and narrow currents that only flow along the ocean surface; It can also be a deep and big torrent, carrying millions of tons of seawater. The nature of ocean currents can be divided into warm currents higher than the water temperature flowing through the sea area and cold currents lower than the water temperature flowing through the sea area. The division of cold current and warm current is based on relative temperature, so the actual temperature of cold current is not necessarily lower than that of warm current; On the contrary, the temperature of warm current is not necessarily higher than that of cold current. Ocean currents are not only distributed on the surface of the ocean, which constitutes the circulation system in the ocean (that is, the surface circulation), but also distributed in the depths of the ocean, which constitutes the deep-sea circulation. According to the flow properties of ocean currents, they can be divided into stable ocean currents with zero acceleration and unstable ocean currents with changing speed and direction. Generally speaking, ocean current refers to steady flow. The large-scale ocean current is the main factor to promote the large-scale exchange of water, heat and salt in different sea areas, and has great influence on climate, marine life, marine deposition and transportation.

The main causes of ocean currents are: atmospheric movement and planetary wind system, density difference, compensation caused by fluid continuity, geostrophic deflection caused by land shape and earth rotation. Among them, the prevailing wind is the main driving force for the formation of ocean currents, but under the action of geostrophic deviation, the directions of wind and ocean currents are not completely consistent with the wind direction.

By the way, ocean current direction refers to the direction of ocean current flow, which is just the opposite of the concept of wind direction. Wind direction refers to the direction in which the wind blows. Ocean current speed refers to the distance (cm/s) that ocean current flows per unit time. In oceanography, the speed of ocean currents is usually expressed in knots. Moving 1 nautical mile per hour is called 1 knot. L nautical miles is equal to 1.852 km, so 1 knot is about 52 cm/sec.

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