南海地区准双周振荡对华南前汛期持续性强降水的影响OA

Persistent heavy rainfall(PHR)during South China's pre-summer rainy season(April-June)is a ma-jor driver of severe flooding and related socioeconomic losses.While intraseasonal oscillations such as the Madden-Julian Oscillation(MJO)are known modulators,the influence and mechanisms of higher-frequency tropical quasi-biweekly oscillations(QBWOs;10-30-day periods)on the intensity and persistence of PHR events remain insufficiently understood.Improving the quantitative assessment of QBWOs over the South China Sea(SCS)and elucidating their coupled ocean-atmosphere processes is essential for enhancing subseasonal pre-dictability.This study systematically investigates the physical mechanisms through which QBWOs over the tropical SCS modulate the occurrence and persistence of PHR in South China.Multiple high-resolution daily datasets cov-ering a climatologically significant period are analyzed,including 1)precipitation observations from the China Meteorological Administration station network;2)atmospheric fields(winds,geopotential height,vertical velocity,and specific humidity)from the NCEP-DOE Reanalysis 2;and 3)sea surface temperature(SST)from the NOAA daily optimum interpolation SST(OISST)dataset.QBWO signals are isolated using a Lanczos band-pass filter(10-30 days),and composite and lead-lag analyses are employed to diagnose coupled variability.Re-sults show that quasi-biweekly convective oscillations over the SCS influence PHR anomalies by modulating low-frequency water vapor transport and vertical motion over South China.On the quasi-biweekly timescale,a negative air-sea feedback emerges,linking SCS convection and SST.Low-frequency cold SST anomalies suppress convec-tion,induce local anticyclonic anomalies and subsidence,and inhibit regional ascent.Subsequently,enhanced solar radiation,reduced upward sensible heat flux,warm-water accumulation driven by southerly winds leads to a tran-sition from cold to warm SST anomalies.During this warming phase,thermally driven direct circulation strength-ens,promoting ascent and cyclonic circulation over South China and enhancing water vapor transport,ultimately supporting the development of intense and persistent rainfall.When warm SST anomalies peak,convection over the SCS is re-energized,local cyclones form,and the vertical circulation undergoes a phase reversal,creating con-ditions less favorable for precipitation over South China. These findings demonstrate that the QBWO over the SCS constitutes a fundamental mode of variability gov-erning the persistence of heavy rainfall during South China's pre-summer rainy season.The identified QBWO-cou-pled mode and the characteristic SST transition from suppressed to enhanced convection provide valuable predic-tors for extended-range(10-30-day)forecasts.Monitoring the phase and amplitude of the SCS QBWO—partic-ularly early signs of SST warming during the suppressed convection phase—may significantly improve early-warning lead times for PHR events.