What are the characteristics of the climate in the past half month? What will the climate be like in the next winter? It is said that this year is the warmest year, why has it been so cold recently? Let's find out.
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Climatic characteristics since winter
The first half of December this year was significantly warmer, and the temperature dropped significantly in the middle of the month. Since December (as of the 18th), most parts of the north have received significantly more precipitation. During this period, the average temperature of the country was -1.3 °C, 0.9 °C higher than that of the same period in normal years, and the temperature in most parts of the country was mainly high.
The country has experienced a "roller coaster" of temperature fluctuations that continued to warm in the early stage and cooled sharply in the later stage. From December 1 to 13, the national average temperature was higher than that of the same period in normal years, which was the highest in the same period in history, and the temperatures in Yunnan and Ningxia were the highest in the same period in history. However, since the 14th, affected by a wide range of cold wave weather, the temperature in most parts of the country has plummeted, and the maximum daily cooling range of some national meteorological stations has exceeded the historical extreme.
Since winter, the average temperature of the country has undergone a "roller coaster" change
Since the beginning of winter, the national precipitation has been nearly 50% higher than that of the same period in normal years. Hebei, Shandong, Shanxi and Inner Mongolia all had the highest precipitation in the same period in history, Beijing and Henan were the second most, and Shaanxi was the third.
From December 14th to 17th, a large-scale cold wave occurred in the mainland, which had the characteristics of wide impact range, long duration, complex phase, large cumulative precipitation, and high overlap between the falling area and the previous process. There are 95 national sites with the maximum cooling range of 20°C or more, and the largest cooling range of 26.3°C in Datong, Shanxi. The area with the maximum cooling range of more than 8°C in the process is about 5.967 million square kilometers, accounting for about 62.2% of the country's land area, of which about 1.625 million square kilometers have a cooling range of more than 14°C. The daily cooling range of 10 national meteorological stations, including Liancheng (16.6°C) in Fujian (16.6°C), Anyuan in Jiangxi (16.5°C), Emeishan in Sichuan (16.5°C), and Guiping (15°C) in Guangxi, exceeded the historical extreme. Affected by the cold wave, the cumulative precipitation in southeastern North China, most of East China, northern and central China generally exceeded 10 mm, of which more than 25 mm in central Jiangsu, central Anhui, central Hubei and other places, and more than 50 mm locally. It will have a certain adverse impact on transportation, facility agriculture, urban operation, and people's production and life. Although the large-scale snowfall in the north has brought many inconveniences to production and life, it has also brought a different scenery to various places.
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Prediction of post-winter climate trends
It is expected that in the second winter (January-February 2024), the intensity of the East Asian winter monsoon will be 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 that of the same period in normal years, the temperature in most parts of the mainland is close to normal, but the cold and warm fluctuations are obvious, or the temperature "roller coaster" will be experienced again. In the latter winter, the precipitation in the central and eastern parts of the continent is more than normal, 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 relatively active, and there may be a phased strong cooling and heavy snowfall process in the northern region, and there may be a phased low temperature rain, snow and freezing weather in the southern part of the Yangtze River and the eastern part of the southwest region. During the intermittent period of cold air, atmospheric diffusion conditions deteriorate, and fog and haze may occur in the Beijing-Tianjin-Hebei region and its surroundings, the Fenwei Plain and the Yangtze River Delta.
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Why is it so cold when the cold wave comes in the warmest year?
The average temperature in the country this autumn is the highest in the same period in history, and the forecast results also show that the temperature in most areas this winter is close to the same period of the year or on the high side. No matter how you look at it, it contradicts the recent cold wave, what is the reason for this?
First, when we talk about whether a year or month is warmer, it is determined not by a single weather event, but by comparing the average temperature over the entire period of time to whether it is significantly higher or lower than that of the same period in history. For example, from November 3 to 7 this autumn, there was a cold wave weather process in most parts of the mainland, during which the temperature fell off a cliff, much lower than the same period in history, but if you calculate the average temperature of the whole autumn, it is the highest since 1961, so it is the "warmest autumn".
Isn't it said that global warming is going on? Why is the cold air still so strong in autumn and winter?
There is a huge temperature difference between the equator and the polar regions, and this difference has caused a strong westerly wind to form around the polar regions around the polar regions, which is called the westerly jet stream. The westerly jet stream acts like a "fence" that restricts the cold air from the polar regions. The stable polar vortex is confined to the Arctic region by a strong westerly jet stream, which is warming 2-3 times faster than the global rate in the context of global warming. As the Arctic warms and the temperature difference between the Arctic and the mid- and low-latitude latitudes weakens, it is difficult to maintain a strong westerly jet, and the cold air in the polar vortex becomes "restless" and more likely to split southward. The cold air from the Arctic is much cooler than in the middle and low latitudes where we live, and the repeated cold waves make us feel "cold and cold".
According to the statistical analysis of historical data, the winter temperature of the continent is generally warm under the background of El Niño, but the periodic cold air activities are more frequent, that is, the fluctuations of cold and warm are more obvious.
However, the intensity of the cold air process is not only affected by El Niño, but also has a lot to do with the fragmentation of the Arctic vortex and the disturbance of the westerly wind belt in the middle and high latitudes. Since mid-December this year, the Arctic vortex has split into two centers, located over Greenland and Siberia. With the violent distortion of the westerly wind belt over Eurasia, the Siberian high has strengthened abnormally, and most parts of the continent have changed from southerly winds to northerly winds, and cold air has moved southward, resulting in a sharp drop in temperature.
On the other hand, the El Niño-induced anomalous anticyclone in the Philippines transported tropical water vapor to the continental region, so the cold wave process from the middle and high latitudes combined with the abundant water vapor conditions from the low latitudes led to a large area of snowfall in the central and eastern parts of the continent. In addition, the increase in albedo in clear skies caused by snow on the ground also made the temperature recovery slower in the later period.
China is a climate change-sensitive area with significant impacts, and although the warming rate is higher than the global average, the intensity of extreme cold waves has not weakened, and the impact range of strong cold air or cold waves has increased. For example, from February 14 to 17, 2020, the nationwide cold wave process affected the mainland, with a cooling of 8~12 °C in most areas, and a local drop of more than 18 °C; snowfall (rain) in Northeast China, eastern North China, Huanghuai and other places, and the maximum snow depth of 7 stations in Jilin Province exceeded 40 cm; heavy rain or torrential rain occurred in Guangdong, Guangxi and other places, and disastrous weather such as hail, strong winds, thunder and lightning, and icy roads occurred in many provinces. From January 20 to 25, 2016, strong cold air affected most of the mainland from north to south, the national process cooling exceeded 6 °C, the area reached 7.86 million square kilometers, 529 counties and cities cooled by more than 12 °C, and 16 counties and cities exceeded 18 °C, 23 stations continued to cool down to break through the historical extreme, and the daily minimum temperature of 67 counties and cities exceeded the historical extreme; on the 25th, Guangzhou experienced the first snowfall since the founding of the People's Republic of China. (WeChat public account of the National Climate Center)