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.摘要本文主要探讨冬季南海南部季节内降水变化的来源，数据主要来自于TRMM和NCEP-DOE资料，方法主要有谱分析和回归分析。研究发现南海南部的降水变化在10–20天和30–60天时间尺度上有不同的来源。10–20天时间尺度上，东亚冬季风超前于南海南部降水异常2天。而在30–60天时间尺度上，两者几乎同时出现。此外，热带东南印度洋上的降水异常超前于南海南部一周左右，这表明热带印度洋上的对流引起的环流异常可能对南海南部30–60天时间尺度上降水异常有重要的作用，但对10–20天时间尺度上降水异常的作用并不明显。
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