Cold wave warning is divided into blue, yellow, orange and red.

The cold wave warning signal is divided into three levels, which are represented by orange, yellow and blue respectively.

Cold wave is a natural weather phenomenon. 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 rain and snow weather along the way. When this cold air reaches a certain standard, it is called a cold wave.

Cold wave is cold air from polar regions or cold zones in winter, which invades the middle and low latitudes on a large scale like tides. When a cold wave strikes, the temperature will drop sharply, accompanied by strong winds, rain and snow. It has a serious impact on industrial and agricultural production, people's lives and human health.

cause

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 powerful westerly belt, so it is difficult to overflow, so there are few cold waves in the southern hemisphere. The northern hemisphere is different. The Eurasian continent and the North American continent connect the Arctic region and the low latitude region, and the tall mountains on the land cut off the westerly belt, resulting in that the westerly wind in the northern hemisphere is much smaller than that in the southern hemisphere, and the westerly belt is discontinuous, while the land heats up and cools down rapidly. 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, so the cold air in the Arctic can go south along these two continents and invade low latitudes.

Because the temperature in the Arctic and Siberia is very low, the density of the atmosphere will increase greatly, and the air will continue to shrink and sink, increasing the pressure. This will form a strong, deep and wide cold high pressure.

When the power of this cold and high pressure system is enhanced to a certain extent, it will flood into China like a tidal burst, bringing severe cooling to China. Cooling, strong wind, rain, snow or freezing weather appear one after another, with a wide range of influence. This is the cold wave.

Every time a cold wave breaks out, the cold air in Siberia will decrease and the air pressure will also decrease. But after a while, the cold air gathered again and piled up, gestating a new cold wave outbreak.

Most of the cold air in the northern hemisphere formed in the Arctic Ocean, then strengthened in Siberia, Canada and other regions, and then further southward.

There is also a strong cold high pressure on the Antarctic continent in the southern hemisphere, and the cold air accumulated on the Antarctic continent is larger and more stable than that in the northern hemisphere. However, due to the existence of a complete and powerful westerly belt in the southern hemisphere, it is difficult for cold air to invade the middle and low latitudes on the Antarctic continent, and the Antarctic is surrounded by a Wang Yang, which will weaken the power of cold air. So there are few cold waves in the southern hemisphere, and the range and frequency of cold air are smaller than those in the northern hemisphere.