Interdecadal changes in the frequency of winter extreme cold events in North China during 1989–2021

How extreme weather and climate events change is an intriguing issue under global warming. By investigating the frequency of extreme cold events (Frexces) in winter over North China (NC), this paper presents robust interdecadal changes in Frexces in NC since the late 1980s. Two shift points are detected at about 2003 and 2013 through a Mann–Kendall test. Three periods are then identified as 1989–2002 (P1), 2003–2012 (P2), and 2013–2021 (P3). Frexces increases from P1 to P2 and then decreases from P2 to P3. Correspondingly, the winter mean Siberian–Ural High (SUH), polar jet stream (PJS), and North Atlantic Oscillation (NAO) show interdecadal changes. The winter SUH gets stronger and the PJS and NAO weaker during P2, while the SUH is weakened and the PJS and NAO strengthened in P3. The stronger SUH and weaker PJS is favourable for cold-air intrusion into NC in P2, and the opposite is true for the weaker SUH and stronger PJS in P1 and P3. The weaker NAO in P2 relates to long-distance wave propagation to Eurasia to strengthen the SUH, while wave activity accompanying the stronger NAO in P3 is confined to western Eurasia. For the all-extreme cold events composite, the area affected by the cold air inducing extreme cold events in NC enlarges northwestward to the West Siberian Plain, and the intensity of the cold air also gets strengthened from P1 to P3.

摘要

全球变暖背景下, 极端天气气候事件的变化受到关注. 本文研究发现, 1989–2021年期间, 华北地区极端冷日数在2003和2013年发生了年代际变化. 极端冷日数先增加后减少. 2003–2012年, 西伯利亚–乌拉尔高压偏强, 极地西风急流偏弱, 有利于冷空气南下入侵华北地区, 华北极端冷日数偏多. 而在1989–2002年和2013–2021年, 情况相反. 虽然三个时段华北极端冷日的强度没有显著差异, 但与其相联系的冷空气强度变得更强, 2013–2021年冷空气中心区域往西北扩张到了贝加尔湖以西地区.