东北春季极端连续无雨日与前冬北太平洋海平面气压的可能联系北大核心

基于1960—2019年中国东北地区108个台站逐日降水资料、JRA-55再分析资料和Hadley中心海温数据,分析了东北地区春季极端连续无雨日的年际变化特征及其与前冬北太平洋地区大气环流和海表温度的关系。研究表明,东北地区春季极端连续无雨日集中在3—4月。当3—4月极端连续无雨日偏多时,贝加尔湖地区存在异常高压,东北地区受偏北气流影响,局地水汽辐散。进一步分析发现,东北地区3—4月极端连续无雨日与前冬1—2月北太平洋地区偶极型海平面气压存在密切联系。该大气模态可以引起同期北太平洋海温呈现出马蹄形异常分布并持续到3—4月。在3—4月,海温异常可以通过改变北太平洋上空的经向温度梯度,引起东亚到北太平洋地区的西风变化,进而有利于贝加尔湖地区出现异常高压。另一方面,海温异常还会增强北半球中纬度的波列活动,东传的波列也可以增强贝加尔湖地区的高压。上述异常环流为东北地区极端连续无雨日的增加提供了有利背景条件。留一交叉验证结果显示,前冬1—2月北太平洋地区偶极型海平面气压可作为东北春季极端连续无雨日的潜在预测因子。

Possible relationship between spring extreme consecutive dry days over Northeast China and North Pacific sea level pressure in the preceding winter

Based on daily precipitation data of 108 stations over Northeast China from 1960 to 2019, JRA-55 atmospheric reanalysis, and Hadley Center sea surface temperature (SST) data, this study investigates the interannual variability of spring extreme consecutive dry days(extreme-CDDs) over Northeast China and its relationship with preceding winter atmospheric circulation and SST over the North Pacific. The results show that the spring extreme-CDDs over Northeast China are concentrated in March-April. With more extreme-CDDs in March-April, there is an abnormal high pressure over the Baikal Lake region, and Northeast China is simultaner ously influenced by the high related abnormal northerly airflow and local water vapor divergence. Further analysis found that the interannual variability of March-April extreme-CDDs over Northeast China has a close relationship with a dipole pattern of sea level pressure over the North Pacific in preceding January-February. This atmospheric pattern can lead to horseshoe-shaped SST anomalies in the North Pacific in January-February, and the SST anomalies can persist into the following March-April and change the meridional temperature gradient over the North Pacific, consequently resulting in westerly anomalies over the region from East Asia to North Pacific and favoring anomalous high over the Lake Baikal region. In addition, the SST anomalies can enhance the mid-latitude wave activity, and the related wave train can propagate eastward to East Asia, also contributing to anomalous high over the Lake Baikal region. The aforementioned atmospheric circulation anomalies provide favorable background conditions for more extreme-CDDs over Northeast China. The leave-one-out cross-validation result indicates that the preceding winter dipole pattern of sea level pressure over the North Pacific can be used as a potential predictor for the spring extreme-CDDs over Northeast China.