On November 30th, with a cold wave coming, Hangzhou suffered a “cliff-like” cooling, and Hang Cheng also ushered in the first snow in the second half of this year. Many people lament that it was still warm in autumn a few days ago, and these days it has entered a cold winter.
Why did this winter come so suddenly? Will there be a cold wave coming later? Can we enjoy the snow scene in Hang Cheng again? How should we keep warm through winter? This issue of “Science+”invited Mao Yanjun, a senior engineer of Zhejiang Climate Center, to predict this winter from the perspective of meteorology.
During the activity, Mao Yanjun gave a lecture on popular science from five aspects: the degree of extreme cold weather, the main reasons of extreme cold weather, the low temperature in winter in Zhejiang, the characteristics of this winter and how to deal with extreme cold weather.
“In meteorology, extreme cold weather is a level of cold. Reduce the temperature from below minus 40℃ to 9..9℃ is divided into eight grades, one of which is MINUS 40℃, which we call’ extremely cold’. Mao Yanjun said that the lowest temperature in genhe city, located in Inner Mongolia Autonomous Region of China, reached MINUS 58℃, making it a cold pole in China, while the lowest temperature in Zhejiang Province appeared in Tianmu Mountain, which was MINUS 20 on January 16, 1958..6℃ is equivalent to “severe cold”. “So for Zhejiang, it has not reached the temperature of extreme cold.”
So what caused the extremely cold weather? Mao Yanjun said that the causes of extreme cold weather are very complicated. Generally speaking, there are three main factors that will lead to extreme cold weather, including abnormal atmospheric circulation and SST in high latitudes, that is, La Nina phenomenon and global warming. “If the first two factors are superimposed at this time, resulting in changes in air pressure and seawater temperature, it is likely to cause extremely cold weather.”
From the history of Zhejiang Province and Hangzhou, the average temperature in Zhejiang Province in winter is 7..22℃, the lowest temperature in Hangzhou appeared on February 6, 1969, 9 below zero..6℃, equivalent to “slight cold” level. Mao Yanjun analyzed that this cold wave was a province-wide cold wave, starting on November 28th and ending on December 2nd. The maximum temperature drop was 12℃ in qingyuan county and 15℃ in Huzhou in 48 hours..6℃。
“This cold wave is characterized by a large cooling range, but the minimum temperature is not low. The lowest in the province is Deqing County on December 1, with a score of 1 below zero..9 degrees. The lowest temperature of this cold wave in Hangzhou appeared on December 1, which was MINUS 0..4 degrees. Mao Yanjun analyzed that last year’s cold wave first appeared on November 6 -8, earlier than this year, but the cooling range and minimum temperature were higher than this year.
Will it be colder this winter than in previous years? During the activity, Mao Yanjun gave the answer-there is a great possibility of staged cold.
Mao Yanjun believes that according to the forecast, from December 2022 to February 2023, La Nina will continue, which will be conducive to the cold air going south. “When La Nina happens, it will lead to the increase of the meridional circulation and the acceleration of the cold air in the north to the south, which will lead to extreme cold weather.” Mao Yanjun analyzed that before November 30, the La Nina phenomenon was very obvious this year. From the monthly analysis, La Nina phenomenon continues throughout the winter, but the intensity of each month is constantly changing. “La Nina phenomenon is strong in December and weakened in February 2023.”
On the other hand, from the analysis of global warming, the temperature in Hangzhou has hit record highs this summer. In the last 20 years, the warmer years in winter account for the majority, and global warming is one of the factors leading to extreme weather. In addition, the uncertainty of cold air activity at high latitudes is great, so there is a great possibility of staged cold.
Mao Yanjun suggested that when extreme cold weather occurs, there will generally be strong winds, freezing rain and snow, and continuous low temperature. Heavy snow will interrupt aviation, railway and highway transportation, and low temperature will interrupt power supply and tight natural gas supply, which will have an impact on people’s daily lives. In terms of coping, when extreme cold weather strikes, we should add clothes in time to keep warm, and at the same time exercise properly, as well as diet to keep out the cold.
(Source: Zhejiang Online)