云南雨日特征及其影响因子分析

Analysis of precipitation day characteristics and influencing factors in Yunnan region

为研究云南雨日特征,基于1960~2019年气象站点观测的逐日降水资料、NCEP/NCAR再分析资料和NOAA的重构海温资料,分析了云南降水日数的时空变化特征及其与海温的联系。结果表明,云南降水主要集中在5~10月,以6~8月最多,并以5 d及以上的长持续降水为主。但是,近年来,云南雨日数有明显下降趋势,EOF分析第一模态表明,云南5~10月雨日变化主要为全区一致型。通过线性相关分析发现,同期北印度洋海温与云南雨日有显著负相关关系,将10°~25°N,55°~65°E区域平均海温定义为北印度洋海温指数,通过海温指数与同期大气环流的回归分析,结果表明:当印度洋海温偏高时,200 hPa西风急流增强,云南地区附近高空有风场辐合,500 hPa低纬度地区位势高度增加,700 hPa低空存在较明显的水汽通量辐散和下沉运动,由印度洋和南海向云南输送的水汽减少,不利于降水发生。通过对比海温低值和高值年的雨日数可以发现,印度洋海温高值年,云南5~10月雨日数均为负距平,反之亦然。研究成果可为金沙江中下游水资源调度和水库群联合调度提供参考。

To study the characteristics of precipitation days in Yunnan,based on daily precipitation data from meteorological stations,NCEP/NCAR reanalysis data and reconstructed SST data from NOAA from 1960 to 2019,the spatio-temporal variation of precipitation days in Yunnan and its relationship with SST were analyzed.The results showed that the precipitation in Yunnan was mainly concentrated in May to October,with the most precipitation from June to August,and the main precipitation persistent in five days or more.However,in recent years,the number of precipitation days in Yunnan had a significant downward trend,and the first mode of EOF analysis showed that the change of precipitation days in Yunnan from May to October was mainly consistent in the whole region.Through linear correlation analysis,a significant negative correlation between SST over the same period in the North Indian Ocean and precipitation days in Yunnan was found.The average SST in the 10°~25°N and 55°~65°E regions was defined as the SST index in the North Indian Ocean.The regression analysis between SST index and atmospheric circulation in the same period showed that when the Indian Ocean SST was high,the 200 hPa westerly jet was enhanced.There was a convergence of wind fields in the upper air near Yunnan,the height increased in the low latitude area of 500 hPa,and the water vapor flux divergence and subsidence movement were obvious in the low altitude of 700 hPa,and the water vapor transported from the Indian Ocean and the South China Sea to Yunnan decreased,which was not conducive to the occurrence of precipitation.By comparing the number of rainfall days of low SST and high SST years,it can be found that the number of precipitation days in Yunnan from May to October in high SST years in the Indian Ocean was negative anomaly,and vice versa.The research results can provide a reference for water resources regulation and joint dispatching of reservoir group in the middle and lower basins of Jinsha River.