近50年中国区域性极端低温事件频发期的气候特征对比分析研究

基于1960—2011年中国冬季区域性极端低温事件库，分别选取20世纪60年代中、70年代中、90年代初、21世纪初以及2008—2011年5个典型的区域性极端低温事件频发时段，从大气内部环流和海温外部强迫两个方面对各频发期的气候异常特征进行了对比分析。总体而言，20世纪60年代冬季区域性极端低温事件的强度大、频次高，在一定程度上表现为年代际尺度的持续性特征，而20世纪70年代中、90年代初、21世纪初则以年际尺度的振荡为主。此外，2008年以来的频发期在大气内部环流和北太平洋海温外部强迫两个方面均呈与20世纪60年代中期较为相似的特征：即欧洲至南亚大范围区域的地表温度异常偏低，欧亚中纬度500 hPa高度场距平呈显著的北正南负模态，急流区南北梯度异常显著，北极涛动具有明显的指数负位相特征，北太平洋海温异常偏暖，太平洋年代际振荡为典型的冷位相等；同时，当前频发期与其他时段的差异较大，特别是与20世纪90年代初的气候特征差异尤为明显。因此，2008年以来区域性极端低温事件频发期所对应的海-气系统异常除了具有全球变暖背景下的一些新特征之外，也初步出现了一些年代际变化的异常信号。

A comparative study of the climatic characteristics of the periods of frequent occurrence of the regional extreme low temperature events in China in the recent 50 years

The climatic characteristics of the typical low-temperature periods of frequent occurrence were compared and analyzed based on the database of the Regional Extreme Low Temperature Events (RELTEs) in winter of China from 1960 to 2011. 5 typical low temperature periods of frequent occurrence (the middle of 1960s, the middle of 1970s, the beginning of 1990s, the beginning of 2000s and 2008-2011) were selected in order to analyze their scale characters. In general, RELTEs in 1960s which are characterized by high intensity and frequency exhibit a persistent feature of decadal scale, while other three frequent periods (the middle of 1970s, the beginning of 1990s and the beginning of 2000s) mainly show the annual oscillation characteristics. Besides, the inner atmospheric circulation and sea surface temperature (SST) external forcing are also compared among these 5 different periods. The results indicate that the current period of frequent occurrence has a similar character to that of 1960s, i.e. the surface temperature is extremely lower than normal from Europe to South Asia, the anomalies of 500 hPa field in the mid-latitudinal Europe-Asia show a north-positive and south-negative pattern, the north and south gradient at the west wind jet area is quite obvious, the AO index has the obvious character of negative phase, and the PDO shows the typical cold phase character with SST of the North Pacific warmer than normal. These characters are obviously different from other periods especially from 1990s. So, in addition to some new features in the background of global warming, the frequent occurrences of RELTEs recently might have implied some anomalous signal with the characters of decadal variability.