2017年华西秋雨异常偏多的环流特征及其成因分析

Circulation features and causes of the anomalous rainfall over the West China in 2017

利用NCEP/NCAR再分析数据集和国家气候中心整编的2000多站逐日降水资料,对导致2017年华西秋季降水异常偏多的大气环流特征及其成因进行分析。结果表明,2017年秋季500 hPa位势高度上欧亚中高纬地区维持一脊一槽环流型,斯堪的那维亚半岛上空有一强大的高压脊,乌拉尔山以东—巴尔喀什湖有一深槽,西太平洋副热带高压异常强大并偏西伸。来自极地的冷空气与来自太平洋和孟加拉湾的暖湿气流交汇于华西地区。华西地区处于东亚副热带西风急流入口南侧的高空辐散区,低层对应较强辐合区和异常上升运动,有利于降水的维持。进一步分析表明,2017年华西秋雨异常偏多是同期巴伦支海海温异常偏暖和中纬度北大西洋海温异常偏暖以及赤道中东太平洋La Nina型海温异常共同作用的结果,其中巴伦支海海温异常与华西秋季降水在年代际时间尺度上存在较为一致的变化,两者自1986年起均处于一致的负位相,而2000年以后两者由负位相转为正位相;秋季中纬度北大西洋海温异常与华西秋雨之间的年际关系也存在明显的年代际转折,在2002年前后由两者不存在关系转为显著正相关关系。以上各个海区海温异常对华西秋雨的影响也通过一系列的大气环流模式模拟试验进行了验证。

Based on the NCEP/NCAR reanalysis data set and daily precipitation data from more than 2000 stations compiled by the National Climate Center,the atmospheric circulation features and its possible causes of the abnormal precipitation in the autumn of West China in 2017 were analyzed.Results indicate that at 500 hPa geopotential height in autumn 2017,the circulation pattern of one ridge and one trough is maintained in the middle and high latitudes of Eurasia,with a strong ridge of high pressure over Scandinavia Peninsula,and a deep trough from the east of Ural Mountain to Balkhash Lake.At the same time,the subtropical high in the western Pacific is very strong and extends westward.The cold air from the polar region converges with the warm and humid air from the Pacific Ocean and the Bay of Bengal in West China.The West China region is located in the upper divergence region to the south of the entrance region of the East Asian subtropical westerly jet.The lower level corresponds to the strong convergence region and the abnormal upward movement,which is conducive to the maintenance of precipitation.Results further show that most of the autumn rain anomalies in West China of 2017 are the result of the combined effects of the abnormal warm Barents Sea surface temperature,the abnormal warm mid-latitude North Atlantic sea surface temperature,and the La Nina type Sea Surface Temperature(SST)anomalies in the equatorial Middle East Pacific.Among them,the interdecadal variations of the Barents Sea Surface Temperature Anomaly(SSTA)and the autumn rain in West China are relatively consistent.Both of them have been in the same negative phase since 1986,but they have changed from negative phase to positive phase since 2000.There is also a significant interdecadal transition between the SSTA in the North Atlantic and the autumn rain in West China in autumn,and the relationship between them has changed from non-existent to positive correlation before and after 2002.The influence of the above SSTA on the autumn rain in West China is also verified by a series of simulation experiments of atmospheric circulation model.