Why is the 'warmest year' so cold? The National Climate Center responds

What has been the climate like for the last half month? What will the weather be like in later winter? This year is said to be the warmest year, why is it so cold recently? Let's find out.

Climate characteristics since winter

The early part of December this year is significantly warmer, and the temperature drop is large in the middle of December. Since December (as of 18), precipitation in most parts of the north has been significantly higher. During this period, the national average temperature was -1.3 ° C, 0.9 ° C higher than the same period of the year, and the temperature in most parts of the country was mainly high.

The whole country experienced a "roller coaster" of temperature fluctuations in the early period and a sharp drop in the late period. The national average temperature from December 1 to 13 was higher than the same period of the year, the highest in the history of the same period, Yunnan and Ningxia were the highest in the history of the same period. However, since the 14th, affected by the large-scale cold wave weather, the temperature has plummeted in most parts of the country, and the maximum daily temperature drop of some national weather stations has broken through the historical extreme value.

Since winter, the average temperature across the country has experienced a "roller coaster" change

Since winter, the national precipitation is nearly 50% more than the same period of the year. The distribution of precipitation is very different, and the central and eastern regions are generally more in the north and less in the south. The precipitation in Hebei, Shandong, Shanxi and Inner Mongolia is the largest in the same period of history, Beijing and Henan are the second largest, and Shaanxi is the third largest.

From December 14 to 17, there was a large-scale cold wave process in China, which had the characteristics of wide influence, long duration, complex phase state, large accumulated precipitation and high overlap with the previous process. In 95 countries, the maximum temperature drop reached or exceeded 20℃, and the maximum temperature drop of Datong process in Shanxi Province was the largest, reaching 26.3℃. The area with the maximum temperature drop of more than 8 ° C is about 5.967 million square kilometers, accounting for about 62.2% of the national land area, among which the temperature drop of more than 14 ° C is about 1.625 million square kilometers. Ten national meteorological stations, including Liancheng in Fujian Province (16.6 ° C), Anyuan in Jiangxi Province (16.5 ° C), Mount Emei in Sichuan Province (16.5 ° C) and Guiping in Guangxi Province (15 ° C), saw their daily temperature drop break the historical maximum. Affected by the cold wave, the accumulated precipitation in southeast North China, most of East China, northern and central China generally exceeded 10 mm, of which central Jiangsu, central Anhui, central Hubei and other places exceeded 25 mm, and local more than 50 mm. It has some adverse effects on transportation, facility agriculture, urban operation and people's production and life. Although the large-scale snowfall in the north has brought a lot of inconvenience to production and life, it has also brought different scenery to various places.

Forecast of climatic trends in late winter

It is expected that in the later winter (January-February 2024), the intensity of East Asian winter monsoon is generally weak, except for the northeast of Inner Mongolia, northern Heilongjiang, most of Tibet, southern Qinghai and other places where the temperature is lower than the same period of the year, most of China's temperature is close to the year, but the cold and warm fluctuations are obvious, or once again experience the temperature "roller coaster". In late winter, the precipitation in the central and eastern parts of China is more, and the precipitation in the rest of the country is close to the same period of the year to less. The cold air activity is more active, the northern region may again appear stage strong cooling, heavy snow process, Jiangnan, the eastern part of the southwest may occur stage low temperature rain and snow freezing weather. During the cold air interval, atmospheric diffusion conditions deteriorate, and fog and haze may occur in the Beijing-Tianjin-Hebei region and its surrounding areas, the Fen-Wei Plain and the Yangtze River Delta.

How come the warmest year ever is so cold

The national average temperature this autumn is the highest in the history of the same period, and the forecast results also show that the temperature in most areas this winter is close to the usual period or higher. What is the reason for the recent cold wave that contradicts everything?

First, we talk about a warmer year or month, not by a single weather event, but by comparing the average temperature over the whole period to whether it is significantly higher or lower than the historical period. For example, from November 3 to 7 this autumn, there was a cold wave weather process in most parts of China, and the temperature during this period dropped off a cliff, much lower than the same period in history, but if the average temperature of the whole autumn is found to be the highest since 1961, it is "the warmest autumn".

What happened to global warming? Why is the cold air so strong in autumn and winter?

There is a huge temperature difference between the equator and the poles, and this difference causes a strong ring of westerly winds to form around the poles, called the westerly jet. The westerly jet stream acts as a "fence" that keeps cold polar air in check. The stable polar vortex is confined to the Arctic by a strong westerly jet stream, which is warming 2-3 times faster than the world under global warming. As the Arctic region warms, the temperature difference between it and the middle and low latitudes weakens, it is difficult to maintain a strong westerly jet, and the cold air in the polar vortex becomes "restless" and is more likely to split south. The cold air from the Arctic is much lower than the temperature in the middle and low latitudes where we live, and the cold wave weather that has appeared many times makes us feel "cold and cold".

According to the statistical analysis of historical data, under the background of El Nino, China's winter temperature is generally warm, but the staged cold air activities are more frequent, which means that the fluctuations of cold and warm are more obvious.

However, the intensity of the cold air process is not only affected by El Nino, but also has a great relationship with the breakup of the Arctic vortex and the disturbance of the mid-high latitude westerlies. Since mid-December this year, the Arctic vortex has split into two centers, one over Greenland and one over Siberia. With the severe distortion of the westerlies over Europe and Asia, the abnormal strengthening of the Siberian high pressure, the prevailing southerly wind in most areas of China changed to northerly wind, and the cold air moved south, resulting in a sudden drop in temperature.

On the other hand, the anomalous anticyclone in the Philippines triggered by El Nino transported tropical water vapor to the mainland of China, so the cold wave process from the middle and high latitude combined with the abundant water vapor condition from the low latitude, resulting in a large range of snowfall process in the central and eastern parts of China. In addition, the increase of clear albedo caused by snow on the ground also made the later warming slow.

China is a sensitive and significant area of climate change. Although the temperature increase is higher than the global average, the intensity of extreme cold waves has not weakened, and the impact of strong cold air or cold waves has increased. For example, from February 14 to 17, 2020, the national cold wave process affected China, with a temperature drop of 8 to 12 ° C in most areas, and a local temperature drop of more than 18 ° C; Snow (rain) weather occurred in Northeast China, eastern North China, Huanghuai and other places, and 7 stations in Jilin Province had a maximum snow depth of more than 40 cm; Guangdong, Guangxi and other places saw heavy rain or torrential rain, and many provinces saw hailstorms, strong winds, lightning and icy roads. January 20-25, 2016, strong cold air from north to south affected most parts of China; A total of 7.86 million square kilometers of China was covered by process cooling exceeding 6 ° C, 529 counties and cities had process cooling exceeding 12 ° C, and 16 counties and cities had process cooling exceeding 18 ° C. The continuous temperature drop in 23 stations broke the historical extreme value, and the daily minimum temperature in 67 counties and cities broke the historical extreme value. Guangzhou saw its first snowfall since the founding of the People's Republic of China on Tuesday.