Cold current and cold wave of cold air

Every winter, there are many strong cold air going south, which causes a large-scale cooling in China. Many domestic media used to call 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 concrete explanation: The cold wave invading China is not always like this. It depends on which part of Siberia and the Arctic has the highest air pressure and which part of China has the lowest air pressure. In addition, it is also influenced by the high mountains in China.

According to statistics, about 95% of cold air passes through central Siberia (70 ~ 90 E, 43 ~ 65 N) and accumulates there. This area is called the key area of cold wave. There are four main routes to invade China from key areas:

(a) Northwest Road (Middle Road) Cold air from key areas passes through the vicinity of China Hetao in the south of Mongolia and directly reaches the middle and lower reaches of the Yangtze River and the south of the Yangtze River. The cold air coming down this route, the cold wave weather north of the Yangtze River is mainly northerly wind and cooling. After reaching the south of the Yangtze River, it may develop with rain and snow due to the active fluctuation of the south branch.

(2) The cold air on the East Road passes through Mongolia to the north of North China. While the main cold air continues to move eastward, the low-altitude cold air turns to the southwest, invades North China through the Bohai Sea, and then reaches the two lake basins from the lower reaches of the Yellow River. The cold air coming down this route often causes strong winds in the northeast of the Bohai Sea, the Yellow Sea, the lower reaches of the Yellow River and the lower reaches of the Yangtze River, backflow in North China and East China, low temperature and even rainy and snowy weather.

(3) The cold air on the west road flows southward from key areas through Xinjiang, Qinghai and the southeast of Qinghai-Tibet Plateau, which has a great influence on the northwest, southwest and south of China, but the cooling rate is not great. However, when the fluctuation of the south branch and the fluctuation of the north branch overlap, it can also cause obvious cooling.

(4) East Road, Jiaxi Road, the cold air of East Road goes south from the lower reaches of Hetao, and the cold air of West Road goes south from the southeast of Qinghai. Two cold air often meet on the east side of the Loess Plateau, between the Yellow River and the Yangtze River, causing a wide range of rain and snow, and then the two cold air meet south, causing strong winds and obvious cooling. Also known as cold flow, cold flow, that is, its own water temperature is lower than the surrounding water temperature. Cold current is an important member of the ocean current family in the world. As the messenger of the cold ocean, it flows from high latitude or polar ocean to middle and low latitude, bringing cool breath to the sea it flows through. Pro-tide is the biggest cold current in the western Pacific.

Compared with the local seawater in the basin, the cold current has the characteristics of low temperature, low salt content, low transparency, slow flow rate, wide range and small depth. In the process of flowing to the middle and low latitudes, the cold current is constantly mixed and exchanged with the surrounding seawater, the temperature and salinity gradually increase, and the upper density decreases, forming a water layer with a sharp change in density-density thermocline between cold water and local water, which has a great influence on the activities of underwater ships. 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 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 cold wave and cold wave are two completely different concepts and cannot be confused.