Variability Of Summer Extreme High Temperature In Northeast China And Its Association With Sea Surface Temperature Anomaly In The North Atlantic

Based on CN05.1 data set of the daily temperature,ERA-interim reanalysis data,OISST data and CMIP6 model data,firstly,the atmospheric circulation of summer extreme high temperature events in Northeast China is classified by hierarchical clustering algorithm,and then the EHT events are classified.The circulation evolution before the summer extreme high temperature events in Northeast China and its relationship with the North Atlantic sea surface temperature anomaly are discussed.The characteristics of all kinds of extreme high temperature events are analyzed.Finally,the classification and change of summer EHT in Northeast China under the global warming SSP245 scenario are predicted by using the results of three models of CMIP6.The main conclusions are as follows.(1)Summer EHT events in Northeast China can be divided into three types namely the westerly-type,blocking-type and wave-train type.The main circulation characteristics of these three extreme high temperature events are as follows:The main feature of atmospheric circulation in westerly-type EHT is that there is a stronger polar vortex than normal and a shallow ridge moves eastward along the Westerlies.With the guide by westerly,it then forms an anticyclone anomaly over Northeast China,thereby resulting in an EHT event over there.When a blocking-type occurs,its corresponding atmospheric circulation shows that a blocking high over the Ural gets stronger,and the northwest airflow sinks and heats Northeast china where locates in the front of the high ridge,thus leading to the extreme high-temperature event.The last type is wave-train type,which has a feature of the "+-+" wave-train type circulation anomaly over Eurasia in the troposphere,and Northeast China is controlled by an anticyclone anomaly and thus forms a high-temperature event.The key sea area affecting the wave-type EHT event is the tropical North Atlantic Ocean.The positive sea surface temperature anomaly in the key sea area where EHT occurs 10-20 days ahead is conducive to the maintenance of the zonal wave-type circulation anomaly over Eurasia in summer.The occurrence of wave-train type EHT events provides favorable conditions.(2)There are significant interannual and interdecadal changes in the number of EHT summer days in Northeast China.The interdecadal transition point is 1992.The number of EHT summer days has been over many years in Northeast China.There is an EU-typeteleconnection wave in the Eurasian continent.Western Europe and Northeast China have positive potential height anomalies.The Northeast China has an anticyclone circulation anomaly.The area is hot and the number of hot days is high.The key North Atlantic sea area that affects the number of EHT days in Northeast China is located in the region(15?25°N,20 ? 70°W).When the sea temperature in this area is high,there are many EHT days in Northeast China.The intraseasonal change in the number of summer EHT days in Northeast China is as follows: the upward trend is the slowest in June,the most significant increase in congestion,and the fastest is the upward trend in August.(3)Using the simulation results of the three models of CMIP6,the classification and change of the EHT events in summer in northeast China under the global warming SSP245 scenario were predicted in the future.In the future warming period,the number of EHT days in the Can ESM5 mode will increase the fastest,at 3.15 d / a,and the BCC-CSM2-MR mode will grow the slowest,at 2.42 d / a.In the prediction results of these three models,The blocking-type EHT events are most frequent and showing an upward trend,The frequency of westerly-type EHT events all showed a downward trend.