青海冬季区域持续性低温事件变化及成因分析

Regional persistent low temperature events in winter in Qinghai Province:variation and causes

利用1961-2017年青海省43站逐日最低气温观测资料,依据区域持续性低温事件判识标准,提取历史上61次典型事件,对影响该类事件的环流演变和前兆信号进行分析。结果表明:事件发展中北半球极涡经历分裂-收缩增强的变化过程,中高纬自西向东逐渐发展为"正-负-正"异常波列状分布;事件发生当日,大西洋地区、乌拉尔山及西伯利亚地区高度场异常偏高,东亚大槽偏深,利于自极地南下的冷空气在西欧上空堆积并沿纬向西风急流路径向东传播影响东亚地区。进一步分析表明,当出现该类事件时,中高纬地区存在三个关键影响区,其中乌拉尔山关键区高度场正异常同此类事件的联系最紧密。

Based on the daily minimum temperature observation data from43 stations in Qinghai Province from1961 to2017,61 typical regional persistence low temperature events were extracted according to the judgment criteria of regional persistence low temperature events,and the corresponding atmospheric circulation were analyzed. The results show that there were obvious precursory signals15 days before a event,especially when there were anomalies in the Ural Mountains,Lake Baikal and Okhotsk Sea,the probability of regional sustained low temperature events in Qinghai was high. While events occurred in winter in Qinghai Province,the probability of positive anomaly at500 hPa height field in Ural Mountains was the highest,followed by that in the Okhotsk Sea and the Lake Baikal. Meanwhile,the longer the events duration,the better the corresponding relation between events and the height field positive anomaly in the key area. Therefore,it is further revealed that the combination and configuration of height field anomalies in the two key areas(Ural Mountains and the Okhotsk Sea)can well explain the typical events in Qinghai in winter;all of which are useful for further improving the multi-scale climate prediction in winter in this area.