平流层NAM异常事件与东北亚地面温度的关系

Relationship of Stratospheric Circulation Anomalies with Surface Temperatures over Northeast Asia

对再分析资料的合成分析表明,10 h Pa北半球环状模（NAM）指数和东北亚地区地面温度（SAT）存在显著的后滞相关关系。正/负位相平流层NAM异常事件往往伴随着东北亚地区正/负异常地面温度变化。负位相NAM指数超前东北亚地面温度异常20～40天,正位相NAM指数超前约20天。定义了有效平流层极端事件（ESE）,并研究了不同标准下平流层NAM异常能够传到对流层的比例。研究表明,NAM异常下传的比例随定义标准的提高而增加。研究结果显示,平流层大气环流异常在一定程度上能够作为先兆因子来延长中国北方冬季对流层天气预报。

Composite analyses using reanalysis data indicate that the time-lag correlations between indices of stratospheric annular mode（NAM） at 10 h Pa and Northeast Asia surface air temperatures（SATs） are statistically significant. Negative/positive stratospheric NAM anomalies are followed by negative/positive SAT anomalies. The leading time of the maximum value of negative NAM indices at 10 h Pa to that of Northeast Asia SATs is 20 to 40 days, and the leading time of positive stratospheric NAM to SATs is about 20 days. Criteria are defined for extreme stratospheric events（ESEs）. The authors also examine the frequencies of stratospheric NAM events that propagate to the troposphere and surface with two different criteria. It is found that the frequency increases as the criterion is higher. The results suggest that signals of stratospheric circulation anomalies are potentially useful for extending tropospheric winter-time weather forecasting for North China.