Permalink : http://hdl.handle.net/2115/75192

JaLCDOI : 10.14943/bull.fish.69.1.1

KEYWORDS : Japan Sea;Bottom Water;gyroscopic waves;nonlinearly interacting triad

We focus on the motions at frequencies close to the local inertial frequency (fs ; vertical component of the Earth’s rotation), i.e., near-inertial waves, at the great depths (> 2500 m) in the Japan Sea. In this confined basin, deep stratification is very weak, especially buoyancy frequency N～0 at the Bottom Water (BW) where the horizontal component of the Earth’s rotation (fc) vector becomes more important for the generation of gyroscopic waves (GsW). The combined effect of both fs and fc is called ‘non-traditional’ effect for linear internal waves. At first, we review that non-traditional effects change the dynamics of near-inertial waves through our original physical interpretation. Its effect is also shown to enable an irreversible transformation of vertical low-wavenumber into vertical high-wavenumber in the BW, when southward propagating near-inertial GsW reflects at the sea bottom. Such transition suggests the predominant near-inertial oscillation of vertical shear currents, which may provide new mechanism for effective mixing in the BW. In later section, as one of the candidates for vertical mixing process, ‘nonlinearly interacting triad of GsW’ is studied in the framework of a fully nonlinear non-hydrostatic numerical model.