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

Mooring ADCF current observations from August 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 M-2, K-1, O-1, P-1, with the barotropic amplitudes being 7.8 cm center dot s(-1), 7.0 cm center dot s(-1), 5.4 cm center dot s(-1) and 3.5 cm center dot s(-1) respectively. The amplitudes of M-2, K-1, O-1, P-1 internal tides vary greatly, which are 12-15 cm center dot s(-1) in the thermocline, and then decrease with increasing depth. The amplitude of the barotropic near-inertial motions is less than 1 cm center dot s(-1), contributing little to the barotropic currents. However, that of the baroclinic near-inertial motions can be as large as 5 cm center dot 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.