Effect of the westward-propagating zonal wind anomaly on the initial development of quasi-biweekly oscillation over the South China Sea during early summer

The characteristics of quasi-biweekly oscillation (QBWO) over the South China Sea during early summer are investigated. Composite results demonstrate that QBWO convection and the meridional wind anomaly exhibit local variation, while the zonal wind anomaly displays zonal propagation. Besides, emergence of the zonal wind anomaly precedes the enhancement of QBWO convection, suggesting the zonally propagating zonal wind anomaly may play a key role in initiating the development of QBWO convection. Diagnostics of the convergence of moisture flux and divergence tendency indicate that QBWO convection is primarily modulated by eddy divergence. Among the contributing factors in the divergence tendency, the β effect associated with the zonally-propagating zonal wind anomaly makes an appropriate phase difference with the eddy divergence, which can contribute to the convergence tendency in the initial stage of QBWO. As a result, QBWO convection and the meridional wind anomaly are enhanced, thus facilitating the initial development of QBWO convection over the SCS during early summer.