Distribution of near-inertial waves in the mixed and deep layers of the East/Japan Sea using a high-resolution wind-forced ocean model

초록

Previous observations of deep near-inertial waves in the East/Japan Sea showed that they were more energetic in the southern region than in the northern region. The significant variation of surface currents in the southern region was suggested to be the cause of this meridionally asymmetric distribution of near-inertial waves, but no clear dynamic explanations were provided. In this study, we investigate the characteristics of near-inertial wave energy distribution in the East/Japan Sea using high-resolution wind-forced ocean model outputs. This model reproduces realistic circulation and stratification through a nudging assimilation of in-situ hydrocasts, satellite measurements, and throughflow observations in the Korea Strait. In addition, the model is forced with hourly wind forcing calculated from a 5-km resolution weather forecast model. Analyses of model outputs at hourly intervals from November 2012 to September 2015 reveal that the near-inertial wave energy distributions in the surface mixed layer are much different from those in the deep layers. The near-inertial wave energy in the mixed layer is stronger and is distributed dominantly in the northern side of the subpolar front during winter months when the wind is strong and the mixed layer develops well. In the deep layers, energetic near-inertial wave patches are found at the southern part of the East/Japan Sea even during winter months, which is consistent with previous observations. Comparisons with background circulation patterns suggest that the distribution of near-inertial waves in the deep layers is highly correlated with anticyclonic mesoscale eddy fields due to their trapping inside those eddies.