北极海冰的年代际转型及极端低温变化特征

Decadal Regime Shift of Arctic Sea Ice and Corresponding Changes of Extreme Low Temperature

摘要: 利用1979~2012年北极海冰范围逐月的距平变化资料，发现北极海冰的减少趋势存在显著的年代际转型，1979~1996年期间北极海冰范围减小速率较慢，为−79.6 km²/month，而1997~2012年则加速融化，海冰面积减小速率(−213.0 km²/month)是1979~1996年的2.7倍。随后探讨了北极海冰年代际转型前后北半球冬季中高纬度极端低温的变化特征及其相应的大气环流特征。研究发现前一时段的1979~1996年期间北半球中高纬度和东西半球极端低温频数均呈现跷跷板式的反位相分布特征，即欧亚大陆高纬度地区极端低温频数存在减少的趋势，西半球特别是格陵兰岛一带以及欧亚中纬度区域极端低温频数具有增加的趋势。这种变化与冬季北大西洋涛动有很大的相关。1997~2012年北极海冰加速融化时期，中高纬度极端低温主要表现为中纬度和极区之间的南北反相振荡特征，即中纬度欧亚大陆极端低温频数增加，北冰洋区与极端低温频数减少。这种变化主要与冬季西伯利亚高压通过影响中高纬欧亚大陆温度的变化进一步影响极端低温的变化有关。

Abstract: Based on anomaly change of monthly Arctic sea ice extent (SIE) from 1979 to 2012, it is found that the decreasing trend of Arctic SIE showed a remarkably decadal regime shift. The melting rate during 1979 to 1996 was slow, which was −79.6 km² per month. While it was −213.0 km² per month from 1997 to 2012 that was 2.7 times of the previous. Subsequently, from the decadal change of Arctic sea ice aspect, variation characters of extreme low temperature (ELT) over mid-high latitudes of the Northern Hemisphere, and related atmospheric circulation characters were discussed. Analyses of ELT frequency trend indicate that, there appears a spatial pattern of out-of-phase oscillation between most of the eastern and western hemispheres during 1979 to 1996. The ELT frequency over Eurasia shows a decreasing trend, and an increasing trend in the western hemisphere, especially over Greenland and middle latitude of Eurasia, which is linked closely to the North Atlantic oscillation. Conversely, there appears an out-of-phase seesaw pattern between the Arctic and northern mid latitude during the accelerated thawing of Arctic sea ice during 1997-2012. The typical character in large-scale surface level pressure anomaly is intensified Siberian high, which suggests more cold air invading into Eurasia continent.