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

Abstract

Using 30-year simulations (1990–2020) with a validated third-generation wave model, we investigated how El Niño-Southern Oscillation (ENSO) drives seasonal wave climate variability in the northern South China Sea (SCS). Results reveal distinct ENSO impacts across seasons. Spring/winter waves respond to monsoon shifts, with El Niño reducing wave heights and La Niña amplifying extreme waves (the 95th-percentile significant wave heights, H_s95) via intensified winter monsoon. An exception occurs in the Gulf of Tonkin, where El Niño elevates H_s95 during the winter monsoon season through localized resonance. Summer/fall waves vary with ENSO's reorganization of tropical cyclone (TC) tracks aligning with ENSO-modulated subtropical ridge changes. Specifically, Eastern Pacific (EP) El Niño concentrates TC near the Luzon Strait, boosting extreme waves in the northeast SCS. Fall coastal energy declines under EP El Niño corresponding to the suppressed basin-wide TC activity. The findings advance predictive insights for the wave climate in monsoon and TC-driven subtropical marginal seas under ENSO variability, addressing the need for localized climate adaptation strategies in marginal seas that are under multi-scale atmospheric forcing.