The disaster predicted in the movie The Day After Tomorrow is not far away. What is a cold wave?

Cold wave is a kind of disastrous weather in winter, and people are used to calling it cold wave. The so-called cold wave refers to the cold air from high latitudes, which is rapidly strengthened in a specific weather situation and invades the middle and low latitudes, causing a wide range of severe cooling, strong winds and rainy and snowy weather along the way. When this cold air reaches a certain standard, it is called a cold wave. According to the regulations of China's meteorological department, if the temperature drop caused by cold air intrusion reaches more than 10 degrees Celsius and the lowest temperature is below 5 degrees Celsius in one day, it is called a cold wave process. But in fact, this standard set by experts does not apply to southern provinces. ?

Because the Antarctic continent is surrounded by vast oceans, the oceans separate Antarctica from other continents. The specific heat capacity of seawater is large, so the temperature of the ocean is slow and the temperature is slow. When cold air passes over the ocean, the slow cooling of the ocean will release a lot of heat and weaken the cold air. In addition, the westerly belt in the southern hemisphere is complete and powerful, and the cold air is trapped in the Antarctic continent by the westerly wind, so it is difficult to go north, so there are few cold waves in the southern hemisphere. The northern hemisphere is different. Eurasia and North America are connected with the Arctic and low latitudes. The mountains on the land cut off the westerly belt, and the land heated up and cooled down quickly. When winter comes in the northern hemisphere, the temperature in these two continents will be as low as tens of degrees below zero, which will not weaken the cold air. Therefore, cold air from the Arctic can travel south along these two continents and invade low latitudes.

China is located in the southeast of Eurasia. From China to the north, there are Mongolia and Siberia. Siberia has a cold climate, and if you go further north, you will reach the northernmost part of the earth-the North Pole. It is colder than Siberia, and the cold period is longer. The cold wave affecting China first formed on the ice surface of the Arctic Ocean, then intensified in Siberia or the Mongolian Plateau, and finally headed south. In North America, cold waves are mainly formed in the Arctic and Canada's Yukon and Hudson Bay.

The outbreak of cold wave has different characteristics in different regional environments: in the northwest desert and loess plateau, there is less wind and snow, which is easy to lead to sandstorm weather; In Inner Mongolia grassland, it is windy, snowy and cold weather; In North China and Huanghuai areas, cold waves are often accompanied by snow. In the northeast, it is characterized by more violent winds and more snow, and the snowfall is the highest in the country; Jiangnan is often accompanied by freezing rain. ?

The cold wave yearbook of China Institute of Meteorological Sciences divides the cold air process into four levels: national cold wave, regional cold wave, strong cold air and general cold air. ?

The freezing rain, snow and ice weather brought by the cold wave is extremely harmful to transportation. The moving speed of the cold wave is tens of thousands of meters per hour, which is similar to the speed of the train. There are three routes that affect the cold wave in China: one is the west road. This is the earliest and most frequent route affecting China. Strong cold air starts from the North Pole, goes south through western Siberia, enters China and Xinjiang, and then invades North China, Central Plains, South China and even Southwest China along the Hexi Corridor. The second is the middle road. Strong cold air flows from Siberia and Lake Baikal in Mongolia, passes through Inner Mongolia Autonomous Region of China, enters North China, and reaches the southeast coastal areas. The third road is East Road. Cold air flows south from northeast Siberia, sometimes through northeast China, sometimes through the Sea of Japan and the Korean Peninsula, and invades the eastern coast of China. The main force of the cold wave going south from this route is eastward, which is generally not very strong and the frequency will not be too much.