两广地区前、后汛期降水异常反位相现象及可能机理

利用1961—2018年中国地面气象台站2 400站中广东省和广西壮族自治区(两广地区)134站逐日降水资料、英国Hadley中心逐月海表温度资料、NCEP/NCAR逐月再分析资料,筛选了两广地区前汛期降水正(负)异常、后汛期降水负(正)异常的年份,即前、后汛期降水异常反位相年份。结果表明,近60 a来,两广地区前、后汛期降水反位相现象与热带西太平洋海温异常存在密切联系。前汛期期间,当热带西太平洋海温为负异常时,大气对该冷源的Rossby波响应引起西北太平洋反气旋环流异常,且水汽由热带西太平洋向两广地区输送并辐合,同时两广地区为水汽的湿平流区域、风场异常辐合区域,其上空受异常上升运动控制,这样的环流配置有利于两广前汛期期间降水正异常。热带西太平洋海温负异常可持续至后汛期期间,大气的Rossby波响应所致的西太平洋反气旋较前汛期偏西北,两广地区为水汽异常辐散区域,同时水汽干平流且风场异常辐散,受异常下沉运动控制,不利于两广地区降水的产生。反之亦然。

Anti-phase relationship between first and second rainy season precipitation anomaly in Guangdong-Guangxi region and its possible mechanism

An anti-phase relationship of precipitation anomaly between first and second rainy seasons is analyzed based on the daily precipitation data of 134 stations in Guangdong Province and Guangxi Zhuang Autonomous Region (hereinafter Guangdong-Guangxi region) at a total of 2 400 surface meteorological stations of China,the monthly sea surface temperature data from the Hadley Center in the UK,and the monthly NCEP/NCAR reanalysis data from 1961 to 2018.This paper selected those years when the precipitation is above/below-normal in first rainy season (April-June) and below/above-normal in second rainy season (July-September) in the Guangdong-Guangdong region.Results show that in the past 60 years,the anti-phase relationship of precipitation anomaly between first and second rainy seasons in Guangdong-Guangxi region is closely related to sea surface temperature (SST) anomaly in the tropical western Pacific.During the first rainy season,when SST anomalies in the tropical western Pacific are negative,the Rossby wave response of the atmosphere to the negative SST anomalies causes an anomalous anticyclone circulation in the western North Pacific.The water vapor is transported and converged from the tropical western Pacific to Guangdong-Guangxi region.Guangdong-Guangxi region is the wet advection area of water vapor and the anomalous convergence area of wind.The anomalous ascending motion of air is dominant in Guangdong-Guangxi region.This circulation configuration is conducive to the positive precipitation anomaly during the first rainy season.The negative SST anomalies in the tropical western Pacific can persist to the second rainy season.The cold source of the heating could also cause an anomalous anticyclone in the western North Pacific through Mastuno-Gill response,but the location of the anticyclone is more northwestward in the second rainy season than that in the first rainy season.The water vapor anomalies are divergent in Guangdong-Guangxi region.Guangdong-Guangxi region is the dry advection area of water vapor and the anomalous divergence area of wind,and is also controlled by the anomalous descending motion.Above circulation configuration is not conducive to the precipitation in Guangdong-Guangxi region.When SST anomalies in the tropical western Pacific are positive,the above situations are opposite.