Origins of intraseasonal rainfall variations over the southern South China Sea in boreal winter

Abstract

This study investigates the origins of intraseasonal rainfall variations over the southern South China Sea (SCS) region in boreal winter. It is found that intraseasonal rainfall variations over the southern SCS have different origins on the 10–20-day and 30–60-day time scales. On the 10–20-day time scale, large rainfall anomalies over the southern SCS are preceded by strong northerly wind anomalies associated with the East Asian winter monsoon (EAWM), by about two days. On the 30–60-day time scale, the strong EAWM-related northerly wind anomalies almost appear simultaneously with large rainfall anomalies over the southern SCS. In addition, obvious large rainfall anomalies occur over the southeastern tropical Indian Ocean about one week before the peak southern SCS rainfall anomalies. It indicates that the convection and related circulation anomalies with origins over the tropical Indian Ocean may play an important role in inducing intraseasonal rainfall variations over the southern SCS on the 30–60-day time scale, but not on the 10–20-day time scale.