Observations of Typhoon‐Induced Deep‐Sea Topographic Rossby Waves on the Continental Slope of the South China Sea

Abstract

Mooring data collected on the northern continental slope of the South China Sea (SCS) are presented to reveal the generation of bottom‐enhanced topographic Rossby waves (TRWs) by typhoons. During the typhoons Nida, Sarika and Haima in 2016, bottom‐enhanced sub‐inertial motions with a period band between 2 and 5 days were observed, whose dispersion characteristics and vertical trapping lengths were theoretically consistent with bottom‐enhanced TRWs. These short‐period sub‐inertial motions appeared to be closely related to typhoon‐induced depth‐independent cross‐slope perturbations in the TRW period. Combining the Ekman pumping theory and observations, it is suggested that the elevated TRW‐band wind stress curl during the typhoons could resonantly excite depth‐independent cross‐slope currents, resulting in stretching and compression of the water column that perturb potential vorticity and then trigger the generation of short‐period TRWs. Reanalysis data from the data‐assimilated Hybrid Coordinate Ocean Model reproduced observed TRWs during the typhoons. Based on 10‐year (2014–2023) reanalysis data and historical track data of typhoons traversing over the SCS, we suggested the widespread occurrence of typhoon‐induced TRWs that could significantly contribute to the bottom flow variation on the continental slopes of the northern SCS.