31 / 2023-07-24 15:07:56

Effect of Continental Slope on Near-Inertial Response to a Typhoon in the Northern South China Sea

Near-Inertial Waves,Stratification and Mixing,Continental Slope,Topography Effect,Tropical Cyclone,Typhoon

Mooring observations of nearly a full-depth of the water column on the continental slope in the South China Sea are presented to reveal ocean near-inertial responses to a typhoon. The typhoon-induced upper ocean (deep-water) near-inertial currents were ＞1.5 m/s (~0.08 m/s), with e-folding time nearly a week (two weeks) and 1.04 (1.08) times of local inertial frequency, while upper ocean (deep ocean) near-inertial currents near-circular (near-rectilinear) polarized. The deep-water near-inertial waves amplified the vertical excursions of temperature and salinity excursions from ~120 m to ~200 m, which reduced the stratification, elevated vertical current shears and enhanced turbulent dissipation rate. Combination of model simulation and observation show that the typhoon-induced near-inertial response is intensified and trapped by the slope topography. Continental slope deforms the near-inertial waves in middle or deep ocean, caused additional middle and near-bottom flows, redistribute the stratification and contribute to mixing. Further analysis shows that topography structures in the across-slope direction, i.e. shallow water, steep slope, gentle slope and deep water has different mechanisms on the deformation of near-inertial waves in the vertical water column. This work gives clues about how ocean topography influences the oceanic dynamic processes, especially after a typhoon in the Northern South China Sea.