Characteristics of Near-inertial Oscillation Influenced by Western Boundary Current of South China Sea

Based on observed velocity data of ADCP for near-inertial wave evolution characteristics of generation and propagation, the difference of shifting effect was found in winter and summer. The background circulation in winter and summer is northeast and southwest, respectively. The diversity of the background flow directions may take an important part in shifting effect of the near-inertial wave motion. According to the different directions of the background circulation, the signals of near-inertial oscillation were screened out and analyzed by synthesis for discussing how the directions of background circulation affected the characteristics of near-inertial oscillation. The mechanism of this effect was explained from the perspective of background vorticity: As the direction of background circulation is the northeast, the background vorticity becomes negative and the effective frequency decreases, the near-inertial oscillation frequency shifts to low frequency band (red shift); contrarily, the background vorticity becomes positive and the effective frequency increases with the southwest background circulation, the near-inertial oscillation frequency shifts to high frequency band (blue shift).