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 and 50 hPa, there are downwellings (upwellings) over tropics and upwellings (downwellings) over mid-latitudes in the upper troposphere and lower stratosphere. The meridional movement of the subtropical westerly jet is related to this secondary circulation, accompanied by anomalies of the South Asian High. 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. With large populations and developed agriculture, understanding the factors influencing summer precipitation in South and East Asia is crucial for predicting future changes. While the quasi-biennial oscillation (QBO) has been recognized as a predictive factor for summer precipitation in these regions, its effects are still uncertain. This study finds that the vertical structure of QBO should be considered when predicting summer precipitation over South and East Asia, rather than the QBO index on a certain level. When the zonal winds over the tropics exhibits the westerlies at 30 and 50 hPa and easterlies at 70 hPa, there's increased precipitation in South Asia, and decreased precipitation in the Yangtze River basin, and vice versa. The possible mechanism is the QBO's vertical structure stimulates secondary circulations, leading to anomalies in the SWJ and the SAH, resulting in summer precipitation changes. These findings could contribute to the extended forecast for summer precipitation in South and East Asia. Summer precipitation in South and East Asia significantly responds to the specific vertical structure of the quasi-biennial oscillation (QBO)Easterlies at 70 hPa and westerlies at 30 and 50 hPa drive more summer precipitation in South Asia while less in Yangtze River BasinThe mechanism is abnormally strong secondary circulation motivated by QBO affects the subtropical jet stream and the South Asian High

Automated summary

This study investigates the responses of Asian summer precipitations to the vertical structure of the quasi-biennial oscillation (QBO) using observations and numerical simulations. The findings indicate that considering the QBO's vertical structure leads to more significant precipitation responses. The study emphasizes the importance of considering the vertical structure of QBO when predicting summer precipitation in South and East Asia.