Opposing Trends of Winter Cold Extremes over Eastern Eurasia and North America under Recent Arctic Warming

Abstract

Under recent Arctic warming, boreal winters have witnessed severe cold surges over both Eurasia and North America, bringing about serious social and economic impacts. Here, we investigated the changes in daily surface air temperature (SAT) variability during the rapid Arctic warming period of 1988/89–2015/16, and found the daily SAT variance, mainly contributed by the sub-seasonal component, shows an increasing and decreasing trend over eastern Eurasia and North America, respectively. Increasing cold extremes (defined as days with daily SAT anomalies below 1.5 standard deviations) dominated the increase of the daily SAT variability over eastern Eurasia, while decreasing cold extremes dominated the decrease of the daily SAT variability over North America. The circulation regime of cold extremes over eastern Eurasia (North America) is characterized by an enhanced high-pressure ridge over the Urals (Alaska) and surface Siberian (Canadian) high. The data analyses and model simulations show the recent strengthening of the high-pressure ridge over the Urals was associated with warming of the Barents-Kara seas in the Arctic region, while the high-pressure ridge over Alaska was influenced by the offset effect of Arctic warming over the East Siberian-Chukchi seas and the Pacific decadal oscillation (PDO)-like sea surface temperature (SST) anomalies over the North Pacific. The transition of the PDO-like SST anomalies from a positive to negative phase cancelled the impact of Arctic warming, reduced the occurrence of extreme cold days, and possibly resulted in the decreasing trend of daily SAT variability in North America. The multi-ensemble simulations of climate models confirmed the regional Arctic warming as the driver of the increasing SAT variance over eastern Eurasia and North America and the overwhelming effect of SST forcing on the decreasing SAT variance over North America. Therefore, the regional response of winter cold extremes at midlatitudes to the Arctic warming could be different due to the distinct impact of decadal SST anomalies.

摘要

在近三十年北极快速增温的影响下, 频繁的寒潮侵袭欧亚和北美, 造成严重的社会、经济影响。本文分析了逐日气温变率在北极快速增暖时期1988/89-2015/16的变化, 我们发现次季节尺度分量贡献的逐日气温方差, 在欧亚东部呈现为显著的增加趋势, 而在北美呈现出显著的减小趋势。冷极值(定义为逐日气温偏冷1.5个标准差以上的天数)的增多主导了东亚逐日气温变率的增加, 而冷极值的减少主导了北美逐日气温变率的减小。欧亚东部冷极值对应的大气环流主要表现为乌拉尔高压脊增强和西伯利亚高压增强, 北美冷极值的大气环流主要表现为阿拉斯加高压脊增强和加拿大高压增强。资料分析和模式模拟结果表明, 乌拉尔高压脊的增强主要与巴伦支海和喀拉海地区的增暖相关, 而与海温异常的相关很弱。阿拉斯加高压脊的增强既受东西伯利亚和楚科奇地区的增暖的影响, 也受北太平洋类太平洋年代际振荡(PDO)型海温的作用。类似PDO型海温异常由正位相向负位相的转换抵消了北极增暖使阿拉斯加高压脊增强的影响, 减少了北美冷极值的发生频率, 由此导致北美逐日温度变率呈现出减小趋势。气候模式多集合模拟结果证实了北极增暖对欧亚东部和北美逐日气温方差增加的驱动作用, 以及海温异常强迫对北美气温方差减少的主导作用。因此, 我们认为, 由于北太平洋海温年代际异常的显著影响, 欧亚东部和北美地区冬季温度冷极值对北极增暖的区域响应表现出反向的变化特征。