As the saying goes: "Xiaohan Xiaohan, frozen into a ball." According to the "Chinese Astronomical Calendar", the "Xiaohan" solar term ushered in at 11:23 on January 5, Beijing time, marking the coldest day of the year-"Count Nine Hantian" has arrived.

On the morning of January 5, the Central Meteorological Observatory issued the first cold wave blue warning for 2021.

The quick freezing mode is turned on and the temperature in many places will hit a new low this winter

  According to the forecast from the Central Meteorological Observatory, affected by the strong cold air, the temperature in the central and eastern regions of my country will generally drop by 6 ℃-8 ℃ from the night of the 5th to the 8th, including parts of western North China, eastern Huanghuai, eastern Jianghuai, and eastern Jiangnan. The temperature drop in the area can reach more than 10℃; after the temperature drop, the 0℃ line of the lowest temperature will press south to southern Jiangnan to northern South China, and the -10℃ line will press south to the Qinling to eastern Jianghuai line.

There will be northerly winds of magnitude 4-6 and gusts of magnitude 7-9 in the Yangtze River Basin and its north.

  Fang Chong, the chief forecaster of the Central Meteorological Observatory, said that although the cooling rate is slightly smaller than the "New Year's Eve" from December 27 to 31, 2020, many places have undergone the previous round of "crushing" of cooling. "Temperature" is relatively low. It is expected that after this round of cooling, the lowest temperature in parts of my country's southern northeast, northern China, and eastern Huanghuai will hit a new low since this winter.

Among them, the lowest temperature in Beijing, Dalian, Jinan and other places will be below -15℃, and the lowest temperature in Shenyang will drop below -25℃.

  As far as Beijing is concerned, starting from January 6, affected by the cold wave, there will be strong winds and continued low temperature weather in Beijing.

The Beijing Meteorological Observatory issued a gale yellow warning signal at 16:30 on January 5th: It is estimated that from 1 am to 22:00 on the 6th, there will be northerly winds of about magnitude 5 and gusts of magnitude 8, 9 in most parts of the city.

The forecast shows that the lowest temperature in Beijing at night on the 6th will be around -16°C.

  According to statistics, the lowest temperature in Beijing since 2000 is -17℃. If the temperature in Beijing during this cold wave is lower than -17℃, it will break the lowest temperature record since the 21st century.

  Experts reminded that due to the previous low base temperature, coupled with this cold air process, the wind is relatively large.

Therefore, people's body temperature will be lower, so keep warm.

La Niña and Arctic sea ice are too small to be ignored

  This year, the cold wave seems to be extraordinarily cold. What caused it?

  According to the statistics of the National Climate Center, since the beginning of winter (December 1, 2020-January 3, 2021), there have been two cold air processes affecting my country in December 2020, which were from December 13 to 15 (National Strong cold air) and December 29 to January 1 (national cold wave).

  According to Yuan Yuan, a researcher at the Climate Prediction Office of the National Climate Center, compared with the same period in history, the number of cold air (including cold waves) is not too high, but both of these are national cold air processes with a large impact and strong intensity.

  Investigating the reason, Yuan Yuan analyzed that since the beginning of winter, the Eurasian mid-high latitudes have been controlled by the meridional circulation of “high west and low east”, and the circulation pattern has not changed much in December last year. At the same time, the East Asian winter monsoon is relatively strong. The interaction between the two is the direct cause of the low temperature in most areas of central and eastern my country since December 2020.

  In terms of climate, the recent peak of the La Niña phenomenon in the equatorial Central and Eastern Pacific and the lack of sea ice in the Arctic in autumn are two signs that cannot be ignored.

Historical statistical analysis shows that in most La Niña years, the meridian of the atmospheric circulation in the middle and high latitudes of Europe and Asia is relatively large in winter, and the cold air activities affecting my country are more frequent and stronger than usual. The temperature in most parts of central and eastern my country is higher than that of the same period of normal years. The probability of being low is also greater.

  In addition, the lack of anomalous sea ice in the Arctic in September 2020 (the second least in history) is also one of the important reasons.

Studies have pointed out that the lack of Arctic sea ice in September is conducive to the stronger Siberian high in winter.

Monitoring in the summer of 2020 shows that the atmospheric circulation in the Arctic region exhibits a typical negative AD phase, with its modal index reaching the lowest value in history, which is also conducive to the stronger Siberian high this winter and the stronger East Asian winter monsoon.

  "In general, the most direct cause of the low temperature in most of the central and eastern parts of my country is the meridional circulation of'high in the west and low in the east' and the strong East Asian winter monsoon. The lack of sea ice in La Niña and the Arctic in autumn will be this winter. Strong wind provides important background conditions." Yuan Yuan emphasized.

  Our reporter Fu Lili