Human activity and simultaneous high-pressure anomalies influence the long-duration cold events of winter in China.

Long-duration extreme cold events in China were often characterized by strong simultaneous high-pressure anomalies (SHA) over the Ural and the North Pacific regions, e.g., 2018. It is unclear how human activity and the SHA influenced the long-duration extreme cold events in China, respectively. Herein, we investigated variations in such long-duration cold events during the past 60 years and contributions of human activity and the related atmospheric circulation pattern. Results show since 2008, the coldest periods in each winter in eastern China have become colder than those in the 1980s and 1990s, which caused an enlarging temperature difference between China and the Northern Hemisphere. We found that an increase in SHA resulted in the cold events colder and longer than a single high anomaly, through a combined reinforcing effect on the high-latitude ridges and a blocking effect on eastward movement of the East Asian trough. The UHA dominates the intensity of cold events, while the PHA modulates the duration of cold air. Comparative analysis indicated that, the enhanced SHA offsets part of the anthropogenic warming effect, resulting in extreme cold events still occurring in warm winters. And strong SHA can increase the probability of the strong cold events to about twice that with weak SHA. It is meaningful to deeply understand variations of cold events under global warming. [ABSTRACT FROM AUTHOR]