Analysis of Paths and Sources of Moisture for the South China Rainfall during the Presummer Rainy Season of 1979–2014

The paths and sources of moisture supplied to South China during two periods of the presummer rainy season(April–June) of 1979–2014, i.e., before and after the onset of the summer monsoon over the South China Sea(SCS),are investigated by using the Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT) model. During the premonsoon-onset period, the moisture transport trajectories are clustered into 6 groups, with four ocean-originating paths providing 83.9% and two continent-originating paths(originating over Lake Baikal and the Persian Gulf) contributing the remaining 16.1% of the total moisture. The two Pacific-originating paths, from the western Pacific Ocean and the East China Sea, combined account for about 46%, the SCS-originating path contributes about 24.3%,while the Bay of Bengal-originating path accounts for 13.6% of the total moisture over South China. The trajectories during the postmonsoon-onset period are clustered into 4 groups, with three southwesterly paths(from the Arabian Sea, the central Indian Ocean, and the western Indian Ocean, respectively) accounting for more than 76% and the sole Pacific-originating path accounting for 23.8% of the total moisture. The formation of the moisture transport trajectories is substantially affected by the topography, especially the Tibetan Plateau and the Indian and Indo–China Peninsulas. The SCS region contributes the most moisture during both periods(35.3% and 31.1%). The Pacific Ocean is ranked second during the former period(about 21.0%) but its contribution is reduced to 5.0% during the latter period, while the contribution from the Bay of Bengal and the Indian Ocean combined increases from 17.1% to 43.2%.