南印度洋海温异常对2020年夏季江淮流域降水的影响

The influence of the southern Indian Ocean sea surface temperature anomalies on the precipitation in the Yangtze-Huaihe River Basin in the summer of 2020

从南印度洋海温异常影响的角度,利用1979-2020年NCEP和NCAR再分析资料,通过南印度洋偶极子(SIOD)指数的定义,研究2020年夏季SIOD对中国江淮流域降水异常的可能影响及大气环流原因.结果表明,1979-2019年江淮流域夏季降水与夏季SIOD指数呈显著负相关,相关系数-0.44,当SIOD指数表现为负(正)异常时,江淮流域夏季降水偏多(少);2020年夏季南印度洋海温表现为SIOD指数负位相,对应江淮流域显著的降水异常偏多.将2020年夏季的大气环流形势与1979-2019年夏季SIOD负异常年份的合成分析进行对比可见,SIOD指数负异常年,对流层高层南亚高压偏强、偏南,东亚副热带西风急流偏南;中层西北太平洋副热带高压偏强、偏北;低层西北太平洋上空水汽输送异常偏多.2020年的环流形势与一般的SIOD指数负异常年类似,但对流层中层表现为中高纬度波动强烈,环流经向度较大,有利于冷空气输送至江淮流域.利用E-P通量进行动力诊断,发现2020年和SIOD指数负异常年,均存在位于60°~80°N上空400 hPa处的辐合中心和位于24°~40°N上空250 hPa处的辐散中心,尤其是在2020年,辐合和辐散的强度更强,不仅对阻塞形势的建立有一定促进作用,有利于冷空气南下与西北太平洋副热带高压西侧的暖湿气流交汇于江淮流域,也有利于东亚副热带西风急流及低空急流加强,为江淮流域降水提供有利的水汽条件和上升运动的增强.

From the perspective of the influence of the southern Indian Ocean sea surface on the temperature anomaly and using the reanalysis data of the NCEP/NCAR from 1979 to 2020,the possible impact of southern Indian Ocean dipole(SIOD)in the summer of 2020 on the anomalous precipitation in the Yangtze-Huaihe River Basin(YHRB)and the causes of atmospheric circulation were studied with the reanalysis data from 1979 to 2020 and the previous definition method of the SIOD index.The result showed that,there was a significant negative correlation between summer precipitation in YHRB and summer SIOD index from 1979 to 2019,with a correlation index of-0.44.When the SIOD index was negative(positive),the summer precipitation in YHRB was more(less).In the summer of 2020,the sea surface temperature of the southern Indian Ocean showed a negative phase of SIOD index,corresponding to the significant precipitation anomaly in YHRB.Those results were found by comparing the atmospheric circulation situation in the summer of 2020 with the synthetic analysis of the negative SIOD index anomaly years in the summers of 1979-2019.In the negative SIOD index years,the South Asian High in the upper troposphere was stronger and southerly,and the westerly jet belt in the East Asian subtropical zone was southward.The Northwest Pacific Subtropical High was stronger and northerly.The water vapor transport over the lower level of the Northwest Pacific Ocean was abnormally high.The circulation situation in 2020 was similar to it during the general negative SIOD index anomaly years but,in the middle troposphere,the circulation fluctuated strongly in middle and high latitudes,and the meridian of circulation was larger,being more conducive to the transport of cold air to YHRB.E-P flux was further used for dynamic diagnosis,and it was found that in 2020 and the negative abnormal years of SIOD index,there were convergent centers located at 400 hPa above 60°-80°N and divergent centers at 250 hPa above 24°-40°N.Especially in 2020,the intensity of convergence and divergence was stronger,which not only promoted the establishment of the blocking situation,but also helped the cold air flow south and the warm and humid air currents on the west side of the Northwest Pacific Subtropical High converge in YHRB.It was also conducive to the strengthening of the East Asian subtropical westerly jet and the low-level jet,thereby providing favorable water vapor conditions and increasing upward movement for precipitation in YHRB.