The Research Team of Lanzhou University Discovered the Characteristics and New Ways of Stratospheric Polar Vortices Affecting Extreme Cold Weather in the Northern Hemisphere
The cold wave is one of the most important extreme weather in the northern hemisphere in winter. Some severe cold wave usually causes widespread cooling and snowfall in densely populated areas of the northern hemisphere, threatening traffic, economy and even life safety. For example, the cold wave that occurred in Europe in February 2018 was called the 'Beast from the East' by the media. In the UK alone, it caused more than 8,000 traffic accidents and hundreds of millions of pounds in property damage. The cold wave that occurred in Asia in January this year also had a serious impact on our country. For example, the minimum temperature in Beijing was close to minus 20 degrees Celsius. Therefore, the prediction of this kind of cold wave is of great significance not only for decision-making but also for the entire society.
Previous studies have shown that the stratospheric atmosphere (10-50 kilometers from the ground) can provide important information for forecasting extreme weather and climate in the troposphere due to its slow evolution characteristics (compared to the troposphere). Especially during some important stratospheric disturbance events, such as the weakening of the stratospheric polar vortex in the northern hemisphere (that is, the polar night jet in the stratosphere changes from westerly to easterly), the influence of the stratosphere on the troposphere is more obvious. However, the impact of the weakening of the stratospheric polar vortex on the risk of cold waves of different intensities has not been systematically studied. In addition, the mechanism by which the Arctic polar vortex affects the cold wave is still inconclusive.
Recently, the research team of Professor Tian Wenshou from the College of Atmospheric Sciences of Lanzhou University and foreign collaborators published a paper with the title of 'Northern hemisphere cold air outbreaks are more likely to be severe during weak polar vortex conditions' in Communications Earth & Environment. (The northern hemisphere cold wave tends to become stronger under weak stratospheric polar vortex conditions). It is pointed out that cold waves in most parts of the northern hemisphere may be more severe when the arctic stratospheric polar vortex is weakened, such as the probability of occurrence of severe cold waves in the mid-latitudes of East Asia will increase by 100%, while the probability of occurrence of moderate cold waves will increase by 40% (see figure). The study further proposed a new way for the weakening of the stratospheric polar vortex to affect the cold wave in the northern hemisphere, that is by affecting the transmission of cold air between the eastern and western hemispheres. Their research provides a scientific basis for forecasting extreme cold weather in advance and scientifically preventing the hazards of cold wave events. The first author of this paper is Jinlong, a postdoctoral fellow in the College of Atmospheric Sciences, Lanzhou University, under the supervision of Professor Tian Wenshou during his Ph.D.
The research was funded by the key projects of the National Natural Science Foundation of China, the Youth Science Foundation of China, and The International Postdoctoral Exchange Fellowship Program.
Figure. Three recent extreme cold wave events in Europe (a), Asia (b) and North America (c), as well as the risk of moderate and severe cold waves at high latitude (d) and moderate latitude (e) in the northern Hemisphere under weak polar vortex conditions in the stratosphere.