Quasi-Biweekly Oscillation of the South Asian High Center in Mid-summer: Its Characteristics and Influence on Rainfall in the Middle and Lower Reaches of the Yangtze River Basin

This study investigated the quasi-biweekly oscillation (QBWO) of the South Asian high (SAH) center in mid-summer and its possible impact on rainfall in the middle and lower reaches of the Yangtze River Basin (MLYRB), using ERA5 reanalysis data and CPC Global Unified Precipitation data from 1979–2023. First, associated with the phase evolution of the QBWO of the SAH center zonally, a general systematic westward propagation of a wave train pattern along the northern margin of the SAH can be identified. Second, energy analysis indicates that this wave train pattern gains energy from the basic flow through both barotropic and baroclinic energy conversion. Compared with barotropic energy conversion, baroclinic energy conversion plays the more important role in the growth, maintenance, and propagation of the wave train pattern associated with the QBWO of the SAH center. Third, the QBWO of the SAH center leads the variation in rainfall in the MLYRB by approximately four days, and might modulate the precipitation in the MLYRB by affecting the coupling of upper- and lower-level circulation anomalies over the MLYRB. The findings of this study suggest that the QBWO of the SAH center could act as potential source of predictability of intraseasonal variation in precipitation in the MLYRB.