NUMERICAL STUDY ON EFFECTS OF THE QINGHAIXIZANG PLATEAU ON FORMATION OF THE URAL BLOCKING HIGH

By employing the improved T42L5 spectral model and utilizing the ECMWF data covering the period from 1 Julyto 7 July 1982,a numerical research on the formation of the Ural blocking system has been made.The results show thatthe model forecasts for the upstream U ral area turn out to be worse if the dynamic effect of the Qinghai-Xizang Plateauis not considered.The correlation coefficient between the model forecasts and observed 500 hPa geopotential heightanomaly decreases by 9% for the 5-day mean,and their averaged root mean square (RMS) error increases 15 m.Due tothe dynamic effect of the Plateau,the trough being on the northwest of the Plateau is barricaded and turns to be atransversal trough.Consequently southwest flow occurs along the northwest of the Plateau in front of the trough,whilenortheast flow prevails over the west of the trough,causing the formation of the blocking high over the Ural area.Whenthe dynamic effect of the Plateau is not taken into consideration,the trough develops and moves southeastward and theUral blocking high changes into a migratory high.All these result in the failure of the simulation.The dynamic effect ofthe Plateau helps to increase the negative vorticities over the Plateau and its north periphery as well as the Ural area,andalso helps to increase the positive vorticities over the Black Sea and the Caspian Sea area.On the other hand,thethermodynamic effect mainly influences the Plateau and its downstream area and plays an less important role in theformation of the blocking high over the upstream Ural area.