The K1 internal tide simulated by a 1/10° OGCM

Abstract

This paper quantifies the K1 internal tide simulated by the 1/10° STORMTIDE model, which simultaneously resolves the eddying general circulation and tides. An evident feature of the K1 internal tide is the critical latitude φc at 30°, which in the STORMTIDE model is characterized by variations from a high energy level equatorward of 30° to a low energy level poleward of 30°. This critical latitude separates the internal tide dynamics into bottom-trapped (at latitudes |φ| > |φc|) and freely propagating (at |φ| < |φc|) motions, respectively. Both types of motions are examined. The bottom-trapping process reveals a gradual vertical decrease of wave energy away from the bottom. The vertical scale, over which the wave energy decrease occurs, is smaller in shallow than in deep water regions. For the freely propagating K1 internal tides, the STORMTIDE model is able to simulate the first three low modes, with the wavelengths ranging from 200–400 km, 100–200 km, to 60–120 km. These wavelength distributions reveal not only a zonal asymmetry but also a poleward increase up to φc, in particular in the Pacific. Such distributions indicate the impact of stratification N and the Coriolis frequency f on the wavelengths. The large wavelength gradient near φc is caused by the wavelength increase from finite values at subcritical latitudes to infinity at φc. Compared to the M2 internal tide, the lower K1 tidal frequency leads to a stronger role of f, hence a weaker effect of N, for the K1 internal tide.