中国冷暖冬季节内交替的时空特征及其与北极极涡振荡的关系

Spatial-Temporal Characteristics of Chinese Warm and Cold Intraseasonal Alternation in Winter and Its Linkage with Arctic Vortex Oscillation

近年来,中国冬季气温除了全国性增暖或降温的年际与年代际变化,其季节内的差异也逐渐明显。本文利用1980~2020年台站及再分析资料,运用时时矩阵的多变量正交经验函数(Multivariable Empirical Orthogonal Function, MV-EOF)分解并结合功率谱分析法,分析了主要反映我国冬季气温在前冬和后冬呈反相变化的主模态特征。结果表明,由白令海–阿拉斯加、北欧和北美区域构成的冬季北极三叶型极涡振荡与我国冬季前后冬的冷暖交替存在密切联系。当冬季北极涛动处于正位相且北极“三叶型”极涡振荡为正位相时,北欧高压脊在前冬加强且异常偏北而后冬位置偏南,引起北极极涡在前冬向极收缩而后冬向赤道扩张,进而影响北极冷空气南下入侵我国,造成我国冬季呈前冬暖后冬冷的特征;而当冬季北极涛动为负位相且“三叶型”极涡振荡为负位相时,北极极涡主要受到白令海–阿拉斯加脊在后冬异常增强的影响,北极极涡横轴由前冬的向南扩张转为后冬向北收缩,对应于我国前冬冷后冬暖的特征。

In recent years, in addition to the inter-annual and inter-decadal variations of national warming or cooling, the intra-seasonal variations of winter temperatures in China have also become more and more obvious. In this paper, using the 1980~2020 station and reanalysis data, we apply the multi-variate orthogonal empirical function (MV-EOF) of the temporal-temporal matrix and combine it with the power spectrum analysis method so as to divide China’s winters into early winter and last winter, in which the temperatures change inversely. It is found that the Arctic “trilobal” vortex oscillation index in winter, which is composed of the Bering Sea-Alaska, Northern Europe and North America, is closely related to the alternation of cold and warm temperatures in winter in China. When the Arctic Oscillation (AO) is in positive phase and the Arctic “trilobal” vortex oscillation is in positive phase, the high pressure ridge of Northern Europe is anomalously to the north in the early winter but to the south in the late winter, which causes the Arctic vortex to narrow down inwardly in the early winter but to expand outwardly in the late winter, and then affects the Arctic cold air to invade China southward, resulting in China’s winters to be characterized by the warmth in the early winter and the coldness in the last winter. When the Arctic Oscillation (AO) is in negative phase and the “trilobal” vortex oscillation is in negative phase, the Arctic vortex is mainly affected by the anomalous enhancement of the Bering Sea-Alaska Ridge in the late winter, and the transverse axis of the Arctic vortex changes from expanding southward in the early winter to contracting north-ward in the late winter, which corresponds to the coldness in the early winter and the warmth in the late winter in China.