Quasi-Biweekly Oscillation of the South Asian High and Its Role in Connecting the Indian and East Asian Summer Rainfall

This study investigates the intraseasonal variation of the South Asian high (SAH) and its lead-lag relationship with the Indian and East Asian summer monsoon rainfall. Results show that the 10–20-day period dominate the zonal oscillation of the SAH between the Iranian mode and the Tibetan mode. The eastward shift of SAH lags the rainfall decrease over northern India by 1–2 days, and leads the rainfall increase over the Yangtze River valley (YRV) by about 3 days. The interactive process among the SAH, Indian rainfall and the YRV rainfall is proposed on quasi-biweekly timescales. The latent heating over northern India contributes to the southwestward shift of a pair of cyclone-anticyclone anomalies from mid-latitude to the SAH region, resulting in the zonal movement of the SAH. The upper-level divergence over eastern China associated with the zonal shift of SAH leads to the rainfall increase over the YRV three days later. This lead-lag relationship may improve the subseasonal rainfall prediction over the two monsoon regions.