How is the cold wave caused?

Strong cold air in the north broke out in the south, and there was severe cooling and windy weather in the path. When the temperature drops to a certain standard, it is called a cold wave. China Meteorological Bureau defines a cold wave as: within 24 hours, the average temperature drops by more than 10℃, and the lowest temperature reaches below 5℃. China has a vast territory and complex terrain, and the climate varies greatly from place to place. Therefore, local meteorological stations can also formulate cold wave standards in their own regions according to local climate characteristics.

The main reason for the cold wave weather is that in the Arctic, due to the weak sunlight, the ground and the atmosphere get less heat, and it snows all the year round. In winter, the direct sunlight passes through the equator and reaches the southern hemisphere. The arctic region is colder and wider, and the temperature is generally below MINUS 40℃-50℃. Large-scale cold air masses gather to a certain extent, and under the action of suitable high-altitude circulation, they will invade southward on a large scale, forming cold wave weather.

Cold wave and strong cold air usually bring strong winds and cool weather, which is the main disastrous weather in winter half a year in China. Cold waves and strong winds are a great threat to coastal areas, such as the cold wave on April 2 1 ~ 25, 1969. Strong winds hit the Bohai Sea, the Yellow Sea and Hebei, Shandong, Henan and other provinces, with land winds of 7 ~ 8 and offshore winds of 8 ~ 10. At this time, the astronomical tide was just right, and the outbreak of cold wave caused the rare storm surge in Bohai Bay and Laizhou Bay for decades. On the northern shore of Shandong Province, the sea water rose by more than 3 meters, washed away the seawall by more than 50 kilometers, and the sea water flowed backwards for 30 ~ 40 kilometers.

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

The freezing rain, snow and ice weather brought by the cold wave is extremely harmful to transportation. For example, 1987 1 1 A cold wave process in the last ten days caused the turnouts of several stations under the jurisdiction of Harbin, Shenyang, Beijing and Urumqi to freeze, the tracks were buried by snow, the communication signals failed, and the train operation was blocked. After the rain and snow, the roads were frozen and skidded, and traffic accidents increased obviously. Cold wave is very harmful to human health. The windy and cool weather can easily lead to colds, tracheitis, coronary heart disease, cor pulmonale, stroke, asthma, myocardial infarction, angina pectoris, migraine and other diseases, and sometimes make patients worse.

cold front

What is a cold front?

Cold front is the most common front in China, and it can move all over the country. However, due to the different configurations and moving speeds of the cold front and the upper trough, the distribution of clouds and precipitation near the cold front is also obviously different, and some mainly appear behind the front; Others mainly appear in the front.

According to the analysis of meteorologists, the weather conditions of cold front can be roughly divided into two types:

The first type: the cold front moves slowly and has a small slope, which is in front of the 700 HPA trough in the air, and is usually called the first type of cold front. This type of cold front, because the cold air mass moves forward on the one hand, makes the warm air mass in front of the front move forward on the one hand, and is forced to slide upward along the front on the other hand. When the water vapor condition is sufficient, cloud system and precipitation will be generated on the front.

Because this cold front is in front of the high-altitude trough, it is conducive to the upward movement of air. Before the front came, the warm air mass was not blue and cloudless. With the arrival of the cold front, there are often cirrus clouds and cirrostratus in the air. As the front approaches, the clouds gradually thicken. The frontage is nimbostratus, and the width of rain area is about 150~200 km.

The second type: the cold front moves quickly and has a large slope. It is often called the second type of cold front behind the trough at 700 HPA or near the trough line. The cold advection above this cold front is strong and the airflow sinks. Only the warm air near the ground front is lifted, but the front has a large slope and a strong airflow moves upward. The weather conditions in winter and summer are obviously different. In summer, the warm air mass is moist and unstable, and the strong cold advection on it becomes more unstable. Therefore, strong cumulonimbus clouds often form near the front line and are arranged near the front line like a cloud embankment. When the cold front comes, there will be thunderstorms and formation precipitation, but the rainfall area is only a few tens of kilometers. In winter, warm air before the front is located in front of the trough, and the airflow rises to form cirrus, cirrostratus, high-level clouds and nimbostratus. Near the ground front, there is a vast continuous precipitation area. After the precipitation stops, there is often a strong wind, also called a dry cold front.

Because the cold front moves fast and slowly, when the cold front moves slowly, the warm air will rise slowly and steadily, so it is easy to appear layered clouds and the rainfall is moderate. When the cold front moves fast, warm air will be lifted rapidly by cold air, which is easy to cause heavy cumulonimbus clouds, accompanied by lightning and heavy rain.

Occurrence time: there are cold fronts in northwest China all year round, strong in winter and weak in summer, with similar frequency. Its shape and moving speed are greatly influenced by the terrain.

The general characteristics of cold front activity: there is cold front activity in East Asia. The frequency of cold front is more in the north than in the south, and the frequency of cold front in the southwest is the smallest. Half a year in winter is more than half a year in summer, with the most in spring and the least in autumn.

Location: The intensity of cold front is strongest in winter, which often directly drives South China and South China Sea, resulting in cold wave weather. The cold front in summer is weak, mainly in the north, and it often brings thunderstorms.

North China is the only place for cold front activities in China. In Northeast China, there are cold fronts all year round, especially in spring and autumn. There are three sources of cold front in these two areas: West Road, Northwest Road and Beibei East Road. The cold front in winter mainly causes cooling and strong winds, and thunderstorms can occur in summer. In spring, cold fronts often cause strong winds and precipitation in Northeast China, but only sandstorms in North China.

After the cold front:

1 temperature: drop

The air pressure drops first and then rises.

Precipitation: There is rain behind the front.

When the front moves, if the warm air mass plays a leading role in pushing the front to move to the cold air side, this front is called a warm front. In China, the warm front often appears on the east side of cyclone center, and it often appears in pairs with the cold front. Generally, when a warm front passes through the boundary, the air pressure decreases and the temperature increases.

Here's one

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