Journal
ADVANCES IN ATMOSPHERIC SCIENCES
Volume 39, Issue 4, Pages 546-552Publisher
SCIENCE PRESS
DOI: 10.1007/s00376-021-1033-y
Keywords
extremely cold winter; anomalous atmospheric circulation; synergistic effect; La Nina; warm Arctic
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Funding
- national key R&D Program of China [2018YFC1505603]
- Key Research Program of Frontier Sciences, CAS [ZDBS-LY-DQC010]
- National Natural Science Foundation of China [41876012, 41861144015]
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This report highlights that the frequent cold surges in the winter of 2020/21 were mainly caused by large-scale atmospheric circulation anomalies in the mid-high latitudes of the Northern Hemisphere, with the synergistic effect of the warm Arctic and La Nina intensifying these anomalies.
In the first half of winter 2020/21, China has experienced an extremely cold period across both northern and southern regions, with record-breaking low temperatures set in many stations of China. Meanwhile, a moderate La Nina event which exceeded both oceanic and atmospheric thresholds began in August 2020 and in a few months developed into its mature phase, just prior to the 2020/21 winter. In this report, the mid-high-latitude large-scale atmospheric circulation anomalies in the Northern Hemisphere, which were forced by the negative phase of Arctic Oscillation, a strengthened Siberian High, an intensified Ural High and a deepened East Asian Trough, are considered to be the direct reason for the frequent cold surges in winter 2020/21. At the same time, the synergistic effect of the warm Arctic and the cold tropical Pacific (La Nina) provided an indispensable background, at a hemispheric scale, to intensify the atmospheric circulation anomalies in middle-to-high latitudes. In the end, a most recent La Nina prediction is provided and the on-coming evolution of climate is discussed for the remaining part of the 2020/21 winter for the purpose of future decision-making and early warning.
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