Effects Of Sea Surface Temperature Changes On The Intensity Of Extreme Precipitation Events In Typical Regions

Global warming increases the frequency and intensity of extreme precipitation events.However,the contribution of extreme precipitation events in different regions remains to be further understood.In this paper,the Time-Square-Gather(TSG)intensity was used to identify the regional extreme precipitation processes in the Yangtze River Valley in China,and the summer extreme precipitation processes in three typical years in 1998,2017,and 2020 were taken as research objects to diagnose the corresponding characteristics of summer water vapor budget and circulation anomalies.Based on long-term sea surface temperature(SST)observations and the empirical orthogonal function(EOF),the SST in three typical years was separated into the warming trend and natural variability.The effects of the SST warming trend and natural variability on summer background water vapor budget were studied using the model sensitivity forcing test,and the quantitative contribution of the SST warming trend and natural variability to regional typical extreme precipitation intensity was recognized.The main conclusions are as follows:(1)The Yangtze River Valley is the large value region of the contribution of summer extreme precipitation to summer total precipitation in China.The three typical extreme precipitation processes in 1998,2017,and 2020 and their summers were accompanied by the convergence of water vapor in the whole atmosphere of the region,and the convergence occurred in the meridional direction.The anomalous anticyclonic circulation over the northwest Pacific formed a stable moisture transport with anomalous southwest winds at the southern boundary of the region.(2)The EOF results show that the time coefficient corresponding to the first mode of global SST anomaly shows a warming trend.In summer when typical extreme precipitation occurs,SST is a strong positive anomaly in the equatorial Indian Ocean and tropical Atlantic Ocean,mainly contributing to the warming trend,while SST anomalies in the equatorial Middle Eastern Pacific are La Ni(?)a type.(3)The numerical model sensitivity test shows that the circulation anomaly of SST anomaly forcing is consistent with the reanalysis data.In 1998,2017,and 2020,the net moisture convergence of the regional atmospheric column is 83%,212%,and 108% of the natural variability forcing,respectively,indicating that the SST warming trend is more important than the natural variability.The SST warming trend and natural variability are the main processes leading to extreme precipitation by forcing anomalous anticyclonic circulation over the northwest Pacific Ocean and causing anomalous water vapor transport over the southern boundary of the Yangtze River Valley.(4)Compared with the whole ocean basin,the SST warming trend in the tropical Pacific contributes less to the regional mean water vapor flux function than that in the Indian Ocean and the North Atlantic,and the forcing effect of the SST warming trend in the Indian Ocean is the most obvious.The contribution of SST natural variability forcing is the strongest in the tropical Pacific,the second in the Indian Ocean,and the least in the North Atlantic.