Anatomy of mode-1 internal solitary waves derived from Seaglider observations in the northern South China Sea

Abstract

Observations from a Seaglider, two pressure sensor-equipped inverted echo sounders (PIESs), and a thermistor chain (T-chain) mooring were used to determine the waveform and timing of internal solitary waves (ISWs) over the continental slope east of Dongsha Atoll. The Korteweg-De Vries (KdV) and Dubreil-Jacotin-Long (DJL) equations supplemented the data from repeated profiling by the glider at a fixed position (depth ~1017 m) during 19–24 May 2019. The glider recorded pressure perturbations were used to compute the rarely-measured vertical velocity (w) with a static glider flight model. After removing the internal tide-caused vertical velocity, the w of the eight mode-1 ISWs ranged from −0.35 to 0.36 m s−1 with an uncertainty of ±0.005 m s−1 due to turbulent oscillations and measurement error. The horizontal velocity profiles, wave speeds, and amplitudes of the eight ISWs were further derived from the KdV and DJL equations using the glider-observed w and potential density profiles. The mean speed of the corresponding ISW from the PIES deployed at ~2000 m depth to the T-chain moored at 500 m depth and the 19°C isotherm displacement computed from the T-chain were used to validate the waveform derived from KdV and DJL. The validation suggests that the DJL equation provides reasonably representative wave speed and amplitude for the eight ISWs compared to the KdV equation. Stand-alone glider data provides near real-time hydrography and vertical velocities for mode-1 ISWs and is useful for characterizing the anatomy of ISWs and validating numerical simulations of these waves.