The ENSO Modulated Wave Climate Over the Northern South China Sea Under the Collective Impact of Monsoon and Tropical Cyclones

Abstract

Wave climate in the northern South China Sea (SCS) was accessed during 1990-2020 based on a high-resolution wave model, encompassing the evaluation of the contributions of monsoon and tropical cyclones under the impact of ENSO activities. Using the Gaussian mixture model, the northern SCS was divided into five subareas according to the wave characteristic variations, and pronounced seasonality was observed in both the mean and extreme significant wave heights (Hs) across all subregions. The highest  occurred near the Luzon Strait all year round, with nonnegligible contributions of swells from the western Pacific Ocean superimposed with wind-seas. The significantly enhanced summer  (95th-percentile Hs) indicates its dependence on both the Asian-Australian monsoon and extra-tropical storms. Further analysis revealed increasing trends in mean and extreme Hs during spring and winter, mainly driven by enhanced winter monsoon. The principal component and regression analyses confirm a robust relationship between the mean and extreme wave climate and ENSO over the last few decades. The analysis of covariate on the monthly  and Hs95 revealed that ENSO influence the northern SCS wave climate mainly through its modulation on the gale frequencies instead of the monsoon activities. Driven by the ENSO-related typhoon track variations, the summer Hs95 during La Niña years tends to be weaker than those during normal years at Guangdong Coast and northwest SCS. The shallow-water Hs during fall, on the other hand, was significantly smaller during El Niño years than those during La Niña and normal years.