Impact of soil moisture anomaly in Northern Eurasian on summer extreme high temperature days in Northeast Asia

Based on the CPC daily maximum temperature dataset from 1979 to 2021, this study identified the summer extreme high temperature events in Northeast Asia, and systematically analyzed the variation characteristics of the number of extreme high temperature days. Combined with NCEP/NCAR reanalysis data and GLDAS soil moisture data, correlation analysis and regression analysis were used to explore the possible influence of soil moisture anomaly in northern Eurasia on the change of extreme high temperature days in Northeast Asia in summer (June to August), and further reveal its potential physical mechanism. The results show that summer extreme high temperature events in Northeast Asia show a significant growth trend, and the high incidence areas are concentrated in northeast China and eastern Inner Mongolia. Further analysis shows that the soil moisture anomaly in the north of Eurasia shows a specific dipole distribution in spring and summer, that is, the soil moisture in the northeast of Europe is dry, and the soil moisture in the north of Lake Baikal and the outer Khingan Mountains is wet, and the land-atmosphere interaction affect atmospheric circulation patterns, contributes to the formation of "positive-negative-positive" zonal wave train structure over Eurasia. The eastward transmission of the wave train transmits the wave energy to the downstream region, contributes to the formation of anticyclonic circulation anomalies and positive geopotential height anomalies over Northeast Asia, which leads to the enhancement of atmospheric subsidence movement in the region, which leads to the surface warming, and finally increases the number of extreme high temperature days in Northeast Asia in summer.