The temperature in many cities has hit a new low this year. What is the reason?

How cold is this winter? This winter is not peaceful. There are a lot of crazy news, which are unprecedented events. Some cars and streets were frozen into ice sculptures, and some small animals were frozen to death in large numbers. There are also many water pipes at home that have not been frozen for years. These are not available in previous years.

Winter comes a little early.

The first large-scale snowfall in autumn and winter this year did come earlier. Since Gregorian calendar 65438+10.3, there has been a large-scale snowfall in many northern provinces, and the snowfall is not small. Even the mountainous area in northern Henan, located in the Central Plains, has been snowing heavily, which really makes farmers feel the first cold weather in autumn and winter.

The autumnal equinox solar term on September 22nd this year is the earliest autumnal equinox since 124 years, and it began to snow ten days later, which makes people say that it is the coldest winter in 60 years. Since the coldest winter in 60 years was put forward by the heavy snow at the beginning of 10, we have to find out how that heavy snow came from.

Please click to enter the picture description (maximum 18 words).

La Nina incident is the first reason.

The cold in early autumn this year is related to the rapid development of La Nina phenomenon. On September 1 1, NOAA first announced the appearance of La Nina. On September 30th, the Australian Bureau of Meteorology and the National Climate Center of China also announced that the equatorial Middle East and the Pacific Ocean had entered the La Nina state. Then it escalated into La Nina event, and the intensity was still moderate.

Atmospheric circulation cools the northern hemisphere.

The world seems to be experiencing the coldest winter, from the severe cold in Europe to the snowstorm in Japan and the persistent low temperature in China. As for the causes of these severe cold events, experts say that it is related to the changes of atmospheric circulation in the northern hemisphere and extremely high polar regions, and there are two most direct reasons.

One is the Siberian high. This is the main system for controlling cold air in the northern hemisphere, especially in Europe and Asia. A strong Siberian high pressure means a windy winter and a cold winter. This winter, the Siberian high pressure is very strong. The second is the transformation of Arctic atmospheric circulation.

Please click to enter the picture description (maximum 18 words).

The arctic is not peaceful either.

There are two atmospheric circulations in the Arctic. One is spreading southward along central Europe, bringing cold weather to Europe. The other is the spread along the eastern part of Asia, which led to the obvious snowstorm in Japan after 65438+ 10/6.

When the Arctic Oscillation is in the normal phase, the pressure field in the middle and high latitudes outside the polar regions forms a situation of "high in the south and low in the north", and the cold air stays in the polar regions; On the contrary, when the Arctic Oscillation is in the negative phase, the situation of "high in the north and low in the south" is formed, and the polar cold air spreads to the south, bringing cold weather to the middle and high latitudes.

From June 5438+1October this year, the Arctic oscillation, which maintained a positive phase for four months, gradually weakened, and quickly developed to a negative phase around June 5438+1October 20, and the cold air that had stayed in the polar region broke out southward. Due to the relatively low air pressure in Europe, Japan and the northwest Atlantic, two favorable paths for cold air to go south have been formed.

The cold weather in some mid-latitude areas of Eurasia is closely related to the change of Arctic atmospheric circulation phenomenon-"Arctic Oscillation". Recently, the Arctic Oscillation is in a negative phase, which causes cold air to invade the mid-latitude region of Eurasia, while warm air travels north to the Arctic region.

Please click to enter the picture description (maximum 18 words).

Global temperature cooling is a trend.

"Since the winter, the strong cold wave in Europe, the snowstorm in Japan and the low temperature in China are all extreme weather events caused by the same atmospheric circulation anomaly." Extreme low temperature freezing is not uncommon in this season. In recent years, there have been different degrees of cold waves and snowstorms in Europe from June 5438 to 10.

However, this year's persistent low temperature disasters in Europe and Asia have attracted close attention from atmospheric science circles at home and abroad. Although Europe was hit by a cold wave, such low temperature weather is not uncommon. European scientists published an article in the British "Independent" saying that the melting and shrinking of Arctic sea ice is the main reason for this abnormal weather.

Please click to enter the picture description (maximum 18 words).

Due to the warming climate, the volume of the Arctic ice sheet is reduced. Once the polar ocean lacks ice sheets, the relatively warm air on its sea surface will move to the cold high altitude, thus affecting the polar atmospheric circulation. In this way, driven by the high-pressure system, the polar cold air moves to the northern hemisphere continent, resulting in a sudden drop in regional temperature.

From 265438 to the beginning of the 20th century, the positive phase of the Arctic Oscillation gradually weakened and began to develop to the negative phase, that is to say, "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, leading to the appearance of cold current and affecting the temperature in the middle and high latitudes of the northern hemisphere.