The Impact Of ISO In The Eurasian Mid- And High-latitude Atmosphere On The European Blocking Frequency In Summer And Their Synergistic Effect On The Extreme High Temperatures In Eurasi

Based on the daily reanalysis data of NCEP from 1979 to 2018,this paper focuses on the structure,propagation and evolution characteristics of atmospheric ISO in the middle and high latitudes of Europe and Asia during 10-30 days in summer,and discusses the relationship between atmospheric ISO in the middle and high latitudes and blocking events in Eurasia.The influence mechanism of ISO in middle and high latitudes on the frequency of blocking events in Europe and their synergistic influence on extreme high temperature events are discussed.The main conclusions are as follows:(1)There are atmosphere intraseasonal oscillation periods of 10-30 days and 30-50 days over the middle and high latitudes,in which there are two modes of propagation of atmospheric ISO: eastward propagation and westward propagation in 10-30 days.During the eastward propagation mode,the height anomaly in the middle and high latitudes of Europe and Asia shows a four-level wave train with positive and negative alternating northwest and southeast inclination.(2)During the eastward mode(westward mode)of phase 6–7(5–6),the positive anomaly of blocking frequency is the strongest in Europe,and the key area is characterized by positive northwest–negative southeast potential height anomaly(positive potential height anomaly).During the eastward propagation(westward propagation)mode phase 1–8(3–4),the blocking frequency in Ural has the strongest positive anomaly,and the south of the key area shows negative potential height anomaly(the key area shows positive potential height anomaly).(3)When the Atlantic region is influenced by the atmospheric ISO in the middle and high latitudes,and the main body of the negative potential height anomaly is located to the west of 30°W,it is more conducive to the formation of a positive NAO type potential height anomaly distribution,the southwest wind anomaly in the Atlantic region,the negative potential vortex anomaly to Europe,and the strong divergence of energy and the eastward transmission of wave flux,which is conducive to the occurrence of downstream European blocking events.(4)The blocking activity in Europe significantly regulated the influence of the two modes of ISO propagation in the middle and high latitudes of Europe and Asia on extreme high temperature events,which increased the frequency of extreme high temperature events in the whole of Europe and northeast China,and decreased the frequency of extreme high temperature events in the south of Europe and the Urals Mountains.