How is the extremely cold weather caused?

Arctic oscillation is a climate concept, and it is a seesaw phenomenon of air pressure change in mid-latitude and high-latitude in the northern hemisphere. Usually, the polar center of the Arctic is controlled by low pressure, and there is a huge cold vortex over the polar region all the year round, surrounded by the surrounding high pressure, while the high pressure is dominant in the mid-latitude region. This situation is called the positive phase of the Arctic Oscillation. In this case, the cold air is confined to the polar regions, so it is not so cold in winter.

However, when the positive phase of the Arctic Oscillation gradually weakened and began to develop to the negative phase, "high in the south and low in the north" gradually changed to "low in the south and high in the north", and the polar center of the Arctic was gradually controlled by high pressure, which pushed the cold air that had been confined to the polar region to the south and brought cold wave weather to the passing area.

This winter, the Arctic Oscillation was in a negative phase, and the cold air in the Arctic quickly spread to the middle and high latitudes. The Ural Mountains blocked the establishment of the high and promoted the strengthening of the Siberian high. This circulation situation is conducive to strong cold air invading Europe, China and Japan in the south, while warm air entering the Arctic in the north, resulting in a situation of "cold in the south and warm in the north".

At the same time, southern China, Japan and the northwest Atlantic are controlled by abnormal cyclone circulation, which is beneficial for the water vapor in the western Pacific to be transported to China and southern Japan, and will merge with the strong cold air in the north to form a blizzard in Japan and a severe low temperature rain in southern China.

Factor 2: Global warming

Global warming leads to the dissolution and regression of Arctic sea ice, which is also the cause of abnormal weather. Due to global warming, the volume of the Arctic ice sheet has decreased by 20% in the past 30 years. Once the polar ocean lacks ice sheets, the relatively warm air on the sea surface will move to the cold high altitude, thus affecting the polar atmospheric circulation. As a result, the polar cold air, driven by the high-pressure system, moved to the northern hemisphere continent, causing the local temperature to plummet. The decrease of Arctic sea ice will affect the development of the high-pressure weather system over northern Russia, bringing the cold winds from the Arctic and Siberia to Europe and the British Isles.

Studies by foreign polar and marine research institutions have confirmed that there is a connection between the reduction of Arctic sea ice and the development of high pressure in polar regions, which affects the air flow pattern in low latitudes in the south. With the decrease of sea ice, a lot of heat is released from the ocean into the cold air, which leads to the warming of the air. Warm air makes the air pressure unstable, which changes the air pressure difference between the North Pole and its south, and finally leads to the change of air flow pattern.

Factor 3: La Nina phenomenon

La Nina phenomenon, also known as anti-El Nino phenomenon, refers to the phenomenon that the sea surface temperature in the eastern and central equatorial Pacific Ocean continues to be abnormally cold, which is the product of the interaction between tropical ocean and atmosphere. The symptoms of this phenomenon are hurricanes, heavy rains and severe cold. For example, at the beginning of 2008, under the influence of this phenomenon, some parts of our country suffered a sustained large-scale low-temperature snow disaster and freezing attack that is rare in history.

La Nina originates from the change of local ocean temperature, which will have a far-reaching impact on atmospheric circulation, which is an important factor affecting climate.