The Key Role of the Vertical Structure of the Stratospheric Quasi-Biennial Oscillation in the Variations of Asian Precipitation in Summer

Based on observations and numerical simulations, this study explores the responses of Asian precipitations in summer to the vertical structure of Stratospheric Quasi-Biennial Oscillation (QBO), and the relevant mechanisms. Compared to the QBO phase defined by a particular level traditionally, considering QBO's vertical structure leads to more significant precipitation responses. When the tropical zonal winds exhibit easterlies (westerlies) at 70 hPa and westerlies (easterlies) at both 30 hPa and 50 hPa, there are downwellings (upwellings) over tropics and upwellings (downwellings) over mid-latitudes in the upper troposphere and lower stratosphere (UTLS). The meridional movement of the subtropical westerly jet (SWJ) is related to this secondary circulation, accompanied by anomalies of the South Asian High (SAH). These circulation anomalies lead to anomalous lower tropospheric circulations, causing abnormal vertical velocities and moisture transports, resulting in increased precipitation over South Asia and decreased precipitation in the Yangtze River basin.