海流流速估算內孤立波海底壓力變化

Abstract

The internal solitary waves (ISWs) are active and have large amplitude in the northern South China Sea. Two mooring sets, each set contains an Acoustic Doppler Current Profiler (ADCP) and a bottom-mounted pressure gauge, were deployed on the continental slope of the northern South China Sea. The mode-1 depression ISWs were clearly seen in the observed current velocity. The ISWs could induce 0.05-0.35 dbar of pressure fluctuation while the tides caused around 0.5-2 dbar of pressure fluctuations. 38 ISWs, caused pressure fluctuations larger than 0.05 dbar, were chosen to study the wave properties. The near bottom pressure disturbances which estimated from current velocity data are compared with the observation. The non-hydrostatic pressure disturbances are also calculated and discussed. The ISW vertical displacement was estimated from the time integration of vertical velocity with the correction of heave motion of background flow. The ISW propagation speed was estimated from the continuity equation. The wave propagation direction was the same as the direction of upper ocean current caused by ISW. These wave properties were used to estimate the current velocities of ISW by calibrating the beam-spreading effect of ADCP measurement. The non-hydrostatic and near bottom pressure disturbances of ISW were estimated from the calibrated current velocities by using the vertical momentum and Bernoulli equations, respectively. The result indicates that the estimated ISW bottom pressure variation could represent the observed pressure variation at bottom. The estimated ISW non-hydrostatic pressure variation and the ISW maximum vertical displacement were proportional to the bottom pressure perturbation. A conclusion is obtained that both the maximum vertical displacement and non-hydrostatic pressure variation caused by the mode-1 depression ISW in the northern SCS could be estimated from the bottom pressure gauge.