Observation of internal tides and near-inertial motions in the upper 450 m layer of the northern South China Sea

Mooring ADCP current observations from Au- gust to November are used to study the barotropic tides, baroclinic tides and near-inertial motions in the upper 450 m layer of the northern South China Sea. The barotropic and baroclinic tides at the mooring station are all dominated by M2, K1, O1, P1, with the barotropic amplitudes being 7.8 cm·s?1, 7.0 cm·s?1, 5.4 cm·s?1 and 3.5 cm·s?1 respectively. The amplitudes of M2, K1, O1, P1 internal tides vary greatly, which are 12―15 cm·s?1 in the thermocline, and then decrease with increasing depth. The amplitude of the barotropic near-iner- tial motions is less than 1 cm·s?1, contributing little to the barotropic currents. However, that of the baroclinic near- inertial motions can be as large as 5 cm·s?1. The inclination of tidal ellipse tends to increase with increasing depth, implying upward propagation of energy, while that of the near-inertial ellipse tends to decrease with increasing depth, implying downward propagation of energy.