Entering the early winter season, "will this winter be a cold winter or a warm winter?" has become a hot topic among people again.In early November, when the highest temperatures at 683 meteorological observation stations across the country exceeded the local November historical extremes, and the highest temperature in Linqu, Shandong Province even reached 32.1°C, many people felt that this year must be a warm winter; but recently, with several waves of cold air heading south, cold waves and heavy snowfalls, everyone seems to have doubts about the judgment of a warm winter.
Figure 1 Live map of the site where the maximum temperature breaks through the monthly extreme value (08:00-16:00 on November 1)
Figure 21Distribution of the maximum cooling amplitude in the national process from November 3 to 7 (unit: ℃)
Image source: Central Meteorological Observatory
So how do you judge whether it is a cold winter or a warm winter? What is the reason why winter starts late in many places in the north? According to the latest climate forecasts, will this winter be a mild one? What role will El Niño play in this?
Warmer ≠ warm winter! Who has the final say between "cold winter" and "warm winter"?
"Whether it's going to be cold or not depends on the beginning of winter" "Whether it's going to be cold or not depends on the frost"... In the early years, people used folk agricultural proverbs to predict the climate in order to arrange farming work reasonably. The words of our ancestors are the result of the long-term evolution of farming history. But is it absolutely accurate and reliable? Not really sure. First, we need to clarify a concept,Cold winter/warm winter evaluates the cold and warm conditions of the entire winter, so the temporary cold and warm conditions do not represent the cold and warm conditions of the entire winter., we cannot draw arbitrary conclusions based on a cold wave or a period of warm weather.
Secondly, cold/warm winter and cold/warm winter are not the same thing. Colder/warmer is just compared to the average conditions. If the temperature is higher than the average, it can be said to be warmer. If the temperature is lower than the average, it can be said to be colder. Cold winter/warm winter are different, there are strict standards.
The National Climate Center formulated the national standard "Warm Winter Level" and it was officially promulgated and implemented in 2008. The national standard "Cold Winter Level" was also released in 2017.The determination of cold winter/warm winter uses the average temperature of the three months of winter as the basic element of determination, and is judged by the difference (anomaly) and standard deviation (a statistic that describes the deviation of a sequence from its average) between the average winter temperature and its annual value..
Taking warm winter as an example, it is divided into single-station warm winter and national warm winter. When the average winter temperature anomaly of a site is greater than or equal to 0.43 times its standard deviation, it is defined as a warm winter at a single site; national warm winter is defined by the percentage of the nationwide warm winter area in the national effective area (also known as the warm winter index). If the warm winter index ≥ 50%, it is defined as a national warm winter.
Image source: China Meteorological News (provided by the author)
According to the criteria for determining warm winters, from 1951 to 2018, there were a total of 20 nationwide warm winter years in my country. However, not all warm winter years are warm winter years, and not all warm winter year temperature anomalies are higher than the average. For example, in the six winters from 2013 to 2018, the temperature anomalies were all positive, but only 2013, 2014 and 2016 were warm winters; while the winter temperature anomaly in 1972 was a negative anomaly compared with the current average, but was an obvious positive anomaly compared with the average used that year. This difference is due to the increase in temperature averages at different stages due to climate warming.
It is worth noting that under the background of global warming, warm winters are occurring more and more frequently in my country.. Of the 20 nationwide warm winters that occurred from 1951 to 2018, 18 occurred after 1985.
This winter is extremely warm, will El Niño take the blame?
Since this autumn, the temperature in northern my country has been abnormally high, and winter has been "late" in many places. Although winter has already begun in most of Northeast China, northwestern North China, and most of northwest China, the onset of winter in most of the above-mentioned areas is later than normal, and in some areas it is more than 5 days later. Is this extremely abnormal climate phenomenon really related to El Niño?
According to the latest monitoring from the National Climate Center, since the equatorial central and eastern Pacific entered the El Niño state in May 2023, the sea temperature index in key areas from May to October has shown a continuous trend of rapid warming, and has exceeded 0.5°C for five consecutive months.It can be determined that a moderate-intensity El Niño event has formed, with moderate intensity and eastern type, and will last until next spring..
The Niño3.4 zone sea temperature index (°C) and SOI index evolve monthly. (Image source: provided by the author)
El Niño is indeed one of the reasons for the warm winter in my country. For our country, the occurrence of El Niño often leads to more precipitation in the south and warmer weather in the north. According to statistics, 14 El Niño events occurred from 1951 to 2000, and my country experienced mild winters 13 times. The most recent El Niño event occurred from November 2019 to March 2020. The average temperature in my country in winter that year was -2.3°C, which was 1.1°C higher than the same period in normal years. It was the fifth highest in the same period in history since 1961. Among them, six provinces (municipalities) including Shandong, Jiangsu, Anhui, Zhejiang, Guangdong and Shanghai experienced the warmest winter since local meteorological records were kept.
However, the temperature in most parts of my country has been late this year. This is mainly due to the zonal circulation that has dominated the middle and high latitudes of Europe and Asia since this autumn. my country is controlled by positive anomalies in the height field. The intensity of the Siberian High is generally weak, and the cold air activity is weak.
Affected by the El Niño event and superimposed on the background of global warming, it is expected that the global average temperature in 2023 is likely to break the record for the warmest year in 2016. The National Climate Center predicts that the temperature in most parts of my country this winter will be close to normal or higher than normal. The previous winter (December 2023) will be warmer, and the latter winter (January to February 2024) will be close to normal. The probability of a warm winter is higher in the north.
The big fluctuations in temperature and temperature are "late but coming". What are the other meteorological reasons behind them?
From "rocket-like" warming to "cliff-like" cooling, the cold wave is "late but arriving." So far, two rounds of strong cold air have swept in with wind and snow. Many people can't help but speculate, is the judgment of El Niño wrong?
my country's climate types are complex and diverse, and there are many influencing factors.Even in mild winter, there will be periods of coldness, and scenes of cold waves and heavy snow will not be absent.. For example, although the winter of 2016 was the warmest since 1951, it still encountered four large-scale cold air processes, with local cooling exceeding 16°C. At present, there will still be periodic cold air activities this winter. It is necessary to pay close attention to the approaching weather forecasts and warnings to prevent possible adverse effects caused by periodic low-temperature rain and snow weather processes.
El Niño is not the same as a warm winter, and the cold wave does not "slap" El Niño in the face. Scientific research shows that increased greenhouse gases, weakened East Asian winter monsoon, volcanic and solar activity are all possible causes of warm winters.
The sharp increase in the content of greenhouse gases such as carbon dioxide in the atmosphere is one of the main reasons for the rise in global average temperatures in recent decades.. The burning of large amounts of mineral fuels and deforestation have led to large-scale emissions of greenhouse gases into the atmosphere. Due to the unique insulation effect of greenhouse gases, they have caused an increase in average temperatures to a certain extent, especially in winter, leading to the formation of warm winters.
The strength of the winter monsoon is the direct cause of changes in winter temperatures in my country.. Generally speaking, weak winter winds mean that cold air masses at high latitudes are inactive, and the cold air that invades our country is less frequent and weak, so winter temperatures are higher and warm winters are more likely to occur. The opposite is true when the wind is strong in winter.
The polar vortex and subtropical high pressure will also affect my country’s winter climate. When the polar vortex area is small and deep in the winter half of the year, the polar vortex tends to shrink near the pole, and cold air gathers in high latitudes near the pole, and is not easy to spread to mid-latitude areas. It has little impact on most areas of my country, and the average winter temperature is high and prone to warm winters. When the polar vortex area is large and shallow, the polar vortex often deviates from the pole, moves in mid- and high latitudes, or moves eastward and south, bringing waves of stronger cold air, causing the temperature in the area north of the Yangtze River in my country to drop significantly.
The strength of the Western Pacific subtropical high located in southeastern Eurasia will also directly affect the cold and warm weather in my country in winter.. Generally speaking, when it is strong, it is conducive to the transport of warm air from the south to the north, and warm winters are likely to occur; when it is weak, it is not conducive to the transport of warm air from the south to the north, and winter temperatures in my country are often low, resulting in cold winters. Since the 1980s, the western Pacific subtropical high has continued to be stronger, which is conducive to maintaining a warm winter climate in my country.
In short, it is difficult to accurately predict that the average temperature exceeds the critical point. Predictions of winter temperatures can often only give a warmer or colder trend. The final judgment of whether it is a warm winter or a cold winter needs to wait until the winter is over and based on live data. For the public, whether it is a warm winter or a cold winter, they need to pay attention to weather forecast and warning information in a timely manner, add clothes to keep warm, and take protective measures.
Author: Cui Guohui, reporter from China Meteorological Administration Meteorological Publicity and Science Popularization Center (China Meteorological News)
Review: Zhou Bing, researcher at the National Climate Center, chief expert in climate services at the National Climate Center
Produced by: Popular Science China