관측과 모델을 통한 남중국해 비선형 내부파에 대한 중규모 순환의 영향

Abstract

This study presents observations of nonlinear internal waves acquired from a 2-D array of pressure-recording inverted echo sounders (PIESs) in the deep basin of the northeastern South China Sea for about 4 months in 2011, with the goal of assessing their propagation features affected by mesoscale circulations. The 2-D array measurements reveal that the northern side of the northeastern South China Sea is dominated by semidiurnal fluctuations, while its southern side is dominated by diurnal ones. The outputs from SUNTANS, a nonhydrostatic and unstructured grid ocean model, agree well with the observed nonlinear internal waves overall with some amplitude and arrival time deviations. We obtain time series of the deviations between our observations and the SUNTANS model simulations at each PIES site. Since the model was run with a horizontally homogeneous temperature profile obtained from a mean of historical observations, the deviations are analyzed in terms of mesoscale variability based on the data-assimilated HYCOM simulation results. We find that the amplitude and arrival time of nonlinear internal waves observed at PIES sites modulate significantly depending on time, which is associated with mesoscale circulation changes during the observation period. Deviations of internal wave arrival time are quite well simulated when they are derived from integration of the first internal-mode phase speed along 2-D ray-traced pssessing their propagation features affected by mesoscale circulations. The 2-D array measurements reveal that the northern side of the northeastern South China Sea is dominated by semidiurnal fluctuations, while its southern side is dominated by diurnal ones. The outputs from SUNTANS, a nonhydrostatic and unstructured grid ocean model, agree well with the observed nonlinear internal waves overall with some amplitude and arrival time deviations. We obtain time series of the deviations between our observations and the SUNTANS model simulations at each PIES site. Since the model was run with a horizontally homogeneous temperature profile obtained from a mean of historical observations, the deviations are analyzed in terms of mesoscale variability based on the data-assimilated HYCOM simulation results. We find that the amplitude and arrival time of nonlinear internal waves observed at PIES sites modulate significantly depending on time, which is associated with mesoscale circulation changes during the observation period. Deviations of internal wave arrival time are quite well simulated when they are derived from integration of the first internal-mode phase speed along 2-D ray-traced p