The effect of Rossby wave propagation and local transient forcing on a heavy precipitation event in spring in eastern China

To explore the evolution mechanism of atmospheric circulation anomalies during the extreme heavy precipitation event in eastern China in early April 2023, based on daily NCEP reanalysis datas, by diagnosing Rossby wave energy dispersion and transient forcing, the role of Rossby wave propagation and local transient wave force for the establish and maintain of double-blocking circulation distribution in middle-high latitude over the Eurasian region and possible precursor are researched, and it is putted forward possible mechanism of double-blocking circulation distribution in middle-high latitude affecting the extreme heavy precipitation in eastern China in early April 2023, the results point out: Under the earlier stronger polar vortex, similar role of polar Eurasian distant correlation(POL) has caused positive abnormal development of potential height over Ural Mountains to Northeast Asia, after that when the North Atlantic stimulates Rossby waves travelling downstream, the combined action of upstream Rossby wave and transient forcing of western cold air over Lake Baikal causes a relatively stable "+-+" type double-blocking circulation distribution over Ural Mountains to Northeast Asia, namely the pattern of the "Ural Mountains blocking high pressure, Baikal Lake trough, and Northeast Asia blocking high pressure": Ural Mountain blocking high pressure and Northeast Asia blocking high pressure are abnormal heat sources, both of which have a relatively positive pressure structure above and below; the Lake Baikal low trough is abnormal cold source, with an oblique pressure structure. The meridional wind anomaly in the double-blocking circulation distribution strengthens the southward (northward) transport of cold (warm) air, When the weak fluctuations of the subtropical westerly wind jet travelling to the eastern China overlaps with the middle-high latitude Rossby wave under in the same phase,"+-+" type Rossby wave in middle-high latitude stretch to south, and strengthen the meridional wind, Under the combined effect of the strong south wind on the southwest side of the low-level anticyclone and the warming of the sinking airflow of the Northeast Asia blocking high pressure, the eastern China has significantly increased in temperature; With strong cold air sinking and moving to south, strong cold front ,cyclone , shear line are formed one after another from the North to the South in eastern China , and at the same time snowstorm, cold wave, strong convection and heavy precipitation occure successive. When the north Atlantic again stimulates the Rossby wave spreading downstream, the eastern North Atlantic blocking high pressure strengthen and move eastward, by which the Ural Mountain blocking High is weakened and collapsed, and the precipitation in the eastern China is ended.