北极海冰的年代际转型与中国冻雨年代际变化的关系

基于1961-2013年HadISST海冰密集度资料,定义了北极海冰的季节性融冰指数,结果显示近几十年来北极季节性融冰范围呈显著的上升趋势,并分别在20世纪70年代末和90年代中期存在显著的年代际转型,相应地,中国冻雨发生频数总体上呈现出显著的减少趋势,但也存在显著的年代际转型。在20世纪70年代末之前,北极季节性融冰范围较小但显著增长,中国冻雨频数年际变化振幅较大,且主要受巴伦支海、喀拉海海冰的影响;20世纪70年代末至90年代中期北极季节性融冰范围维持振荡特征,没有显著的线性趋势,中国冻雨频数变化振幅减小,与北极海冰相关较弱,主要相关因子为北大西洋及北太平洋海表温度变化;而90年代中期以后,北极海冰融化加快,特别是2007年以后,季节性融冰范围大大增加,而中国冻雨频数处于低发时段,其变化与太平洋扇区海冰及堪察加半岛附近海温呈显著负相关,季节性融冰的显著区域也从东西伯利亚海逆时针旋转向波弗特海-加拿大群岛北部扩张,同时向北极中央区扩张。不同年代影响冻雨的海温或海冰关键海区不同,产生特定的大气环流异常响应,进而影响到我国冻雨。

Decadal regime shift of Arctic sea ice and associated decadal variability of Chinese freezing rain

Based on the HadISST sea ice concentration (SIC) data from 1961-2013, we define the Arctic sea ice seasonal melting index and analyze the spatial and temporal characteristics of Arctic sea ice seasonal melting extent. It turns out that in recent decades there are two significant decadal regime shift, late 1970s and the middle of 1990s respectively. Before the late 1970s, the oscillation of Arctic sea ice extent was decrease under the background of global warming, the seasonal melting extent (SME) was small but increased significantly; during the late 1970s and the middle of 1990s, the oscillation of the SME was maintain and had no significant trend; while after the middle of 1990s, although there is a hiatus of the global warming, the melting of Arctic sea ice is accelerating, especially after 2007, during which Arctic sea ice SME is greatly increased. Besides that, as the time goes by, the significant SME area expanded anticlockwise from the East Siberia sea to Beaufort Sea-north Canadian Arctic Archipelago gradually, and expand to the central Arctic at the same time. Correspondingly, the total frequency of Chinese freezing rain (CFR) is decreasing during the past several decades and also has significant decadal regime shift. The inter-annual amplitude of the total frequency of CFR was large during 1962-1979, then turned small during 1980-1996, with close relation to SST instead of sea ice. After 1997 the total frequency of CFR is at a low stage, but is increasing, which may mostly be influenced by Arctic sea ice variability. The key area of SST or SIC that influence CFR are different during different decadal epochs, resulting in certain atmospheric background circulation anomalies. There is a consistency between the change of CFR and the SME, which means that the decadal regime shift of the Arctic sea ice may be the cause of the decadal regime shift of Chinese freezing rain.