Summer Extreme Temperature In China And Its Association With The Previous Soil Moisture

China is one of the countries frequently suffered by meteorological disasters.Doing research on extreme climate and improving the accuracy of extreme climate events prediction would be significant. Summer extreme temperature is one of the most common extreme climate disasters in China. Sea surface temperature and atmospheric circulation factors are common used in summer extreme temperature prediction models, but soil moisture is seldom considered in summer extreme temperature prediction models in China. Could soil moisture improve the accuracy of extreme temperature prediction is needed to be understood. Firstly, based on the observational soil moisture data of Chinese 778 agrometeorological stations form 1992 to 2010, ERA-interim reanalysis soil moisture data, JRA55 reanalysis soil moisture data, NCEP-DOE R2 soil moisture data and the Twentieth Century Reanalysis(20CR) data, by calculating four statistical quantities mean bias,correlation coefficient,standard deviation of differences, and ratio of standard deviations, the applicabilities of these four reanalysis soil moisture datasets over the east of Northwest China, North China and the Jianghuai region are investigated by using the Brunke ranking method and the empirical orthogonal function analysis(EOF). Secondly,Based on the maximum and minimum surface air temperatures of 587 stations in China, ERA-interim reanalysis soil moisture(SM)data and the extended reconstructed sea surface temperature (ERSST) data, the possible linear connection between the previous (spring and winter) sea surface temperature (S ST), soil moisture and summer extreme temperature in China during 1979 to 2009 is investigated. Statistical summer extreme temperature prediction models were developed by using Barnett-Presisendorfer Canonical Correlation Analysis(BP-CCA), Ensemble Canonical Correlation(ECC) method and newly defined summer extreme temperature indices. And the scores for the prediction models with predictive skill in the independent sample tests were also calculated.Lastly, combined with synthesis of difference method, the possible physical process of that how soil moisture anomalies in spring affecting the summer extreme temperature in the Jianghuai region and Northeast China is discussed. The main conclusion are as followed.(1) in the spring and summer, the JRA55 data showed to be less humid in the east of Northwest China, the average deviation of most stations is between -0.08 m3 · m-3 to 0.08 m3 · m-3. The ERA_interim, NCEP-DOE R2, 20CR data is larger than the observational data, the average deviation in the south of North China and the Jianghuai region is less than the average deviation in the north of North China and the east of Northwest China. For the interannual variability, the ERA_interim reanalysis data shows the best relationship with the observational data. The ERA_interim reanalysis can best reproduce the variation tendency of the observed soil moisture data in the east of Northwest China, North China and the Jianghuai region. Overall, the ERA_interim reanalysis data shows the best relationship with the observed soil moisture data, followed by the JRA55, NCEP-DOE R2 data, and the 20CR data shows the worst.(2) the summer extreme temperature in China has close relationship with the previous SST and SM anomaly, the spatial distribution of the previous SST anomaly was similar to the PDO pattern, and the previous SM anomaly in South China, in the Tibetan plateau, in Northeast China and in the west of Northwest China. The cross validation tests showed that BP-CCA models based on the previous winter predictors had higher predictive skill than that based on the previous spring predictors.BP-CCA models based on SM had higher predictive skill than that based on SST.The independent sample tests showed that ECC models based on the previous SM and SST had high predictive skill for summer extreme temperature in China. The study shows that the previous soil moisture and sea surface temperature contain valuable signals for summer extreme temperature in eastern China, and can be considered for the summer extreme temperature prediction operations.(3)Based on the synthesis of difference conclusions, the upper potential height and wind anomalies in Northeast China and the Jianghuai region has close relationship with the previous SM anomalies in Jianghuai region, Northeast China,North India and Myanmar. 500hPa potential height anomalies and 200hPa zonal westerlies anomalies over North China and Lake Baikal are most significant influence factors for summer extreme temperature in Northeast China. For the Jianghuai region, the local 500hPa potential height anomalies and 200hPa zonal wind anomalies are important influence factors.