春季/夏季型El Ni?o对中国夏季降水变化的影响

Spring and summer El Ni?o events and their influences on summer precipitation in China

利用中国气象局160站的逐月降水资料,NCAR/NCEP再分析资料以及美国CPC提供的Ni?o3. 4区指数,对比分析了SP、SU两类El Ni?o事件发展年、衰减年中国夏季降水和东亚环流特征的差异。结果表明:1) SP型El Ni?o事件发展年全国以少雨为主要特征,衰减年降水呈"北多南少"分布; SU型发展年,降水异常呈"三明治"型分布特征,衰减年降水偏多区域增大。2) 850 h Pa风场上,SP型El Ni?o事件发展年夏季风偏强,但反气旋性风场异常位置偏东偏北,衰减年夏季风还保持强劲,且反气旋性风场异常偏西偏南;而SU型发展年东亚夏季风偏弱,衰减年夏季风偏强。3) 500 hPa高度场上,SP型事件发展年夏季,我国受东亚夏季风影响总体偏弱,来自低纬地区的暖湿水汽向我国大陆输送不足;衰减年,受偏强东亚夏季风影响,来自低纬地区的暖湿水汽向我国腹地输送。SU型发展年,受相对活跃的冷空气影响,内蒙到华北地区多雨;衰减年,受偏强夏季风影响,冷暖气流在我国黄河及以北地区交汇。4)比较两类El Ni?o事件发生时对流层低层和高层特征表明:在SP型事件发展年,我国大陆上空,除内蒙和东北外,基本为下沉异常,衰减年基本为上升异常;在SU型发展年,我国大陆上空皆为显著的下沉异常,衰减年为弱下沉异常,但在偏强夏季风的作用下,降水偏多区域增大了。

In this study,the anomalies of summer precipitation in China,and the atmospheric circulation over East Asia,were compared during the spring(SP)and summer(SU)El Nino developing and decaying years,in order to improve the understanding of the relationship between the El Nino events and climate anomalies in China,and to provide references for climate predictions.The percentages of the precipitation anomalies in China;horizontal wind anomalies at 850hPa;geopotential height anomalies at 500hPa;velocity potential anomalies;and divergent wind anomalies at 850hPa and 200hPa,respectively,were also analyzed.This study utilized the monthly precipitation data of 160 stations in China for the period ranging from 1950to 2016,which were provided by the National Climate Center of China Meteorological Administration.The monthly geopotential height,wind,and specific humidity data were provided by the American National Centers for Environmental Prediction.The Nino 3.4 index data were provided by the American Climate Prediction Center.The results obtained in the study were as follows:1)During the SP El Nino developing years,the majority of China experienced below-normal precipitation levels,and displayed a"higher northern-lower southern"rain trend during the decaying years.During the SU El Nino developing years,the precipitation anomalies were observed to be"sandwich"formations,in which the regions receiving more rain were larger during the decaying years;2)It was determined that at 850hPa during the SP El Nino developing years,the summer monsoons were strong,and had maintained strong levels up to the decaying years.However,during the SU El Nino developing years,the East Asian summer monsoon were observed to be weak,before turning stronger in the decaying years;3)It was found in this study that at500hPa during the SP El Nino developing years,the influences of the East Asian summer monsoons on China's climate were weaker,and the warm and moist water from the low latitude regions was insufficient to become transported to the China's Mainland.However,during the decaying years,the warm and moist water from the low latitude regions was affected by the stronger summer monsoons,and was easily transported to the hinterland of China.During the SU El Nino developing years,having been affected by the relatively active cold air movements,it was observed that the Inner Mongolia and northern China regions had experienced above-normal rain levels.However,during the decaying years,having been affected by the strong summer monsoons,the cold and warm air had intersected north of the Yellow River;4)This study's comparison results of the lower and upper levels of the troposphere revealed the following:During the SU El Nino developing years,there were sinking anomalies observed over China,with the exceptions of Inner Mongolia and Northeast China;During the decaying years,there were rising anomalies observed over China.During the SU El Nino developing years,there were significant subsidence anomalies observed over China,and during the decaying years,there were weaker subsidence anomalies evident.However,having been affected by stronger summer monsoons,the regions which had experienced below-normal precipitation became larger.