西南雨季降水异常海气背景场特征

Characteristics of Sea-Air Background Field of Precipitation Anomalies in the Rainy Season in Southwest China

为了研究中国西南雨季降水异常海气背景变化场特征,利用西南地区1960~2022年81站共63年的逐日气象观测降水量资料、同期英国哈德莱中心月平均海表温度(SST)资料(格点分辨率为1˚ × 1˚)、欧洲气象资料中心(ERA-interim)的月平均降水再分析资料(格点分辨率为0.25˚ × 0.25˚)、欧洲气象资料中心月平均位势高度(200 hPa,500 hPa,700 hPa及850 hPa)和风场等再分析资料(格点分辨率为2.5˚ × 2.5˚)。通过相关分析、合成分析等方法,对西南雨季降水异常海气背景变化场特征进行了研究分析,结果表明:1) 海温异常年份做西南地区雨季降水合成分析时,当前一年冬季和当年春季西太平洋暖池海域的海温异常偏高而东太平洋冷舌海温异常偏低,当年夏秋季和雨季同期北印度洋海域整体海温偏高时,西南雨季降水偏少,降水多在青藏高原,川南部分区域及贵州西南部发生;而当四季和同期海域海温异常偏低时,此时降水偏多,且多集中发生在云南大部、贵州和川东等区域。2) 降水异常年份做海温合成分析时,当西南雨季降水偏多时,四季和同期海域海温整体异常偏低;当西南雨季降水偏少时,夏秋季和同期北印度洋海温分布并不是全区一致型,而是呈正IOD位相分布形势。3) 大气环流异常形势表明:当四季和同期海域海温异常偏高时,高层南亚高压异常东移,中层西太平洋副热带高压进一步西伸,低层来自孟湾和南海–西太平洋的水汽输送减少,导致西南地区除川西地区外大部降水减少,而高原雨季降水增加;在海温异常偏低时,南亚高压和西太平洋副热带高压强度较弱,位置并没有明显的东移和西伸,低层水汽输送又进一步增加,除川西高原降水减少以外,西南地区大部雨季降水增加。In order to study the characteristics of the sea-air background variation field of precipitation anomalies in the rainy season in southwest China, the daily meteorological observation precipitation data of 81 stations in southwest China for a total of 63 years from 1960 to 2022, the monthly mean sea surface temperature (SST) data of the Hadley Center in the United Kingdom during the same period (grid resolution of 1˚ × 1˚), and the monthly mean precipitation reanalysis data of the European Meteorological Data Center (ERA-interim) (grid resolution of 0.25˚ × 0.25˚), European Meteorological Data Centre (ERA-interim) monthly mean geopotential altitude (200 hPa, 500 hPa, 700 hPa and 850 hPa) and wind field reanalysis data (grid resolution of 2.5˚ × 2.5˚). Correlation analysis and synthesis analysis were used to study and analyze the characteristics of the sea-air background variation field of precipitation anomalies in the rainy season in southwest China. The results show that: 1) When the SST anomaly year is used for the synthesis analysis of precipitation in southwest China, the SST in the warm pool of the western Pacific Ocean is abnormally high in the winter and spring of the current year, and the SST in the cold tongue of the eastern Pacific is abnormally low, and when the overall SST in the northern Indian Ocean is high in the summer and autumn of the year and the same period of the rainy season, the precipitation in the southwest rainy season is low, and the precipitation mostly occurs in the Qinghai-Tibet Plateau, some areas of southern Sichuan and southwest Guizhou. When the sea surface temperature is abnormally low in the four seasons and the same period, the precipitation is more at this time, and most of it occurs in most of Yunnan, Guizhou and eastern Sichuan. 2) When the SST synthesis analysis was performed in the precipitation anomaly years, when the precipitation in the southwest rainy season was too much, the overall sea surface temperature in the four seasons and the same period was abnormally low. When the precipitation in the southwest rainy season is low, the distribution of SST in the northern Indian Ocean in summer, autumn and the same period is not consistent across the whole region, but shows a positive IOD phase distribution pattern. 3) The anomalies of atmospheric circulation show that when the sea surface temperature is abnormally high in the four seasons and the same period, the upper South Asian high anomaly moves eastward, the middle western Pacific subtropical high extends further westward, and the low-level water vapor transport from the Ben Bay and the South China Sea-Western Pacific decreases, resulting in a decrease in precipitation in most parts of southwest China except for western Sichuan, and an increase in precipitation in the plateau during the rainy season. When the SST is abnormally low, the intensity of the South Asian high and the western Pacific subtropical high is weak, and the position does not move eastward or westward significantly, and the low-level water vapor transport further increases, except for the decrease of precipitation in the western Sichuan Plateau, the precipitation in most of the southwest region increases in the rainy season.