Impact Of The Previous Soil Moisture Anomaly In The Indochina Peninsula On The Super Strong Plum Rain In 202

In the summer of 2020,a super Mei-yu event occurred in the Yangtze River Basin(YRB),causing enormous economic losses and human casualties.Recent studies have investigated the possible causes of this super Mei-yu event from the perspective of anomalous atmospheric circulation activities and sea surface temperature(SST)anomalies;however,the influence of land surface processes has not garnered considerable attention.This study investigates the possible contributions of land surface processes to this extreme event based on observational analysis and numerical simulations,and shows that antecedent soil moisture(SM)anomalies over the Indo-China Peninsula(ICP)have a vital influence on the super Mei-yu in 2020.The results show the following:(1)The negative SM anomalies in May over ICP result in a significant increase in the precipitation over YRB.The antecedent dry soil over ICP increases the surface temperature and sensible heat flux.The “memory” of soil allows the anomalies to persist into the Mei-yu period.The heating of the lower atmosphere by the surface strengthens the western Pacific subtropical high(WPSH),which causing an anomalous anticyclone from ICP to the western Pacific and thus enhance the southwesterly winds and vertical motion over YRB.Consequently,the water vapor flux and convergence are strengthened,which resulted in the significant increase of precipitation in Mei-yu period.(2)Sensitivity experiments based on the Weather Research and Forecasting Model further confirm the results of observational analysis and show that the SM anomalies in May over ICP increase the precipitation by 10.6% from June to July over YRB.The results of the warm air heated by ICP surface significantly warms the lower troposphere from the ICP to the western Pacific under the influence of the background wind,thus increasing the geopotential height and inducing an anticyclone.Meanwhile,warm advection increases the meridian temperature gradient,which is conducive to the occurrence and development of continuous frontal precipitation(3)The results of statistical analysis and numerical experiments show that SM anomalies over ICP and Indian Ocean(IO)SST anomalies have a synergistic effect on the super Mei-yu in 2020.Correlation analysis prove that SM anomalies in May over ICP have significantly negative correlations with the WPSH intensity,water vapor flux and convergence,vertical motion and precipitation over YRB in the background of IO SST warming.The results of numerical experiments based on the Community Earth System Model prove that there is a synergistic effect between SM anomalies in May over ICP and IO SST warming.IO SST anomalies and ICP SM anomalies increase the precipitation in YRB by 8.1% and 14.1% in June to July.With the synergistic effect of the two factors,the precipitation over YRB increases by32.3%.These findings can improve understanding of the mechanism of the super Mei-yu event in2020 and facilitate the prediction of extreme Mei-yu events.