The South China Sea (SCS) serves as the main source of moisture for rainfall in Southern China (SC) and the meridional moisture transport to SC is dominated by wind changes during the first rainy season (April–June). El Niño-Southern Oscillation (ENSO) and Tropical Northwestern Pacific (TNWP) variability modulate the SC rainfall through anomalous anticyclonic circulation over the western North Pacific by strengthening the SCS meridional moisture transport to SC. However, our study indicates that the SCS is not only the intermediary in which ENSO or the TNWP affects the SC rainfall but also plays an independent role in the modulation of the SC rainfall. Notably, the SCS meridional moisture transport has a lower impact on the SC rainfall during the second rainy season (July–September), especially in July. At that time, the main cause of the SC rainfall is the southward moisture flux anomaly across its northern boundary with the anomalous cyclone over SC. This cyclone suppresses the moisture flux out of SC and leads to moisture convergence in SC. Moreover, we present a new concept by analyzing internal differences of moisture circulation during the second rainy season. Either strengthening the meridional moisture flux into SC across its southern boundary or suppressing the moisture flux out of SC across its northern boundary is important depending on whether or not the moisture from the SCS can converge in SC, which is mainly determined by the amplitude of moisture transport fluxes in SC.

南海（SCS）是华南（SC）降雨的主要水分来源，而在第一个雨季（4月至6月），向南向子午的水分输送主要受风的变化影响。厄尔尼诺-南方涛动（ENSO）和热带西北太平洋（TNWP）的变化通过加强南海经向南海的子午水汽输送，通过北太平洋西侧的异常反气旋环流来调节南海降水。然而，我们的研究表明，SCS不仅是ENSO或TNWP影响SC降雨的中介，而且在SC降雨的调制中起着独立的作用。值得注意的是，在第二个雨季（7月至9月），特别是在7月，南海经向水汽输送对南半球降雨的影响较小。那时候，造成南半球降水的主要原因是南半球北边界的水汽通量异常以及南半球上空的气旋异常。该旋风分离器抑制了水分从SC流出，并导致SC中的水分收敛。此外，我们通过分析第二个雨季期间水分循环的内部差异，提出了一个新概念。加强沿南边界进入SC的子午水分通量或抑制沿南边界流出SC的子午水分通量很重要，这取决于SCS的水分是否可以在SC中收敛，这主要取决于水分的幅度SC中的传输通量。该旋风分离器抑制了水分从SC流出，并导致SC中的水分收敛。此外，我们通过分析第二个雨季期间水分循环的内部差异，提出了一个新概念。加强沿南边界进入SC的子午水分通量或抑制沿南边界流出SC的子午水分通量很重要，这取决于SCS的水分是否可以在SC中收敛，这主要取决于水分的幅度SC中的传输通量。该旋风分离器抑制了水分从SC流出，并导致SC中的水分收敛。此外，我们通过分析第二个雨季期间水分循环的内部差异，提出了一个新概念。加强沿南边界进入SC的子午水分通量或抑制沿南边界流出SC的子午水分通量很重要，这取决于SCS的水分是否可以在SC中收敛，这主要取决于水分的幅度SC中的传输通量。