A monthly-climatological parameterization of the surface leading-crestline morphology for internal solitary waves in the northeastern South China Sea

Abstract. Internal solitary waves (ISWs) in the northern South China Sea are among the most energetic worldwide, and ISWs can cause severe impacts on offshore platforms and underwater operations; rapid forecasting of the propagation process of ISWs is therefore a practical need in ocean engineering. In the actual ocean, the leading-crestline morphology at the ocean surface often provides a general indication of the propagation and evolution of the underlying internal wave. This study develops a parametric representation of surface-expressed leading-crestline morphology for the east-of-Dongsha segment of the Luzon Strait–Dongsha corridor. Specifically, leading crestlines are extracted from sea-surface-height-gradient (SSHG) fields of nonhydrostatic MITgcm simulations forced by World Ocean Atlas 2018 monthly stratification, using Canny edge detection and density-based clustering. The analysis results indicate that, under the assumption of monthly climatological stratification, the crestlines binned by their along-corridor location cluster around a common, location-dependent propagation morphology that is represented by cubic polynomial curves and summarized in monthly coefficient tables. Evaluated against independent satellite-derived crestlines, the representative curves achieve a mean root-mean-square error (RMSE) of approximately 0.01° in longitude and a mean of 0.870. Consequently, by analyzing the monthly average climate-state leading-crestline morphology across different months of the year, we can identify the key characteristics of internal wave propagation in the northeastern South China Sea.