Spatiotemporal variation of ocean sound speed anomalies and acoustic propagation effects in South China sea during the typhoon YINXING

Typhoon-induced perturbations of the ocean thermohaline structure can substantially alter the underwater acoustic propagation environment. However, continuous, high-resolution observations within the typhoon core forcing region remain scarce, limiting quantitative constraints on the three-dimensional evolution of sound speed profiles and their effects on long-range acoustic propagation. In this study, an array of eight SEAWING autonomous underwater gliders deployed in the South China Sea was used to investigate Typhoon YINXING (2024, No. 22). Full-depth sound speed profiles reconstructed from in situ glider temperature and salinity measurements were used to drive the Monterey-Miami Parabolic Equation model for forward acoustic propagation simulations. The vertical anomaly structure was strongly depth-dependent, with the 0–50 m and 50–150 m layers showing point-estimate contributions of 4.3%–11.0% and 16.2%–45.5%, respectively. The peak anomaly exhibited marked spatial heterogeneity: the median peak anomaly was 2.07 m/s for gliders within 50 km of the typhoon track and 0.91 m/s beyond 50 km. However, the small sample size and non-monotonic point-to-point variability do not support a generalized parametric radial decay law. Under the baseline configuration of 400 Hz and 50 m source/receiver depths, the post-typhoon condition produced a range-averaged transmission-loss increase of approximately 4.90 dB over 10–40 km relative to the pre-typhoon condition. Sensitivity analyses further reveal clear frequency- and receiver-depth dependence of this response. Near-field observations indicate a residual shallow sound-speed anomaly during the approximately nine-day post-passage window, but this persistence should be interpreted as a combined spatiotemporal response because the glider underwent a net horizontal displacement of 193.6 km and subsequent atmospheric disturbances occurred.