Mapping low-mode internal tides near Hawaii using TOPEX/POSEIDON altimeter data

Abstract

Objective maps of M2 internal-tide variability are derived from TOPEX/POSEIDON altimeter data obtained near the Hawaiian Ridge. An estimate of the wavenumber spectrum shows that the radiation is dominated by a few spectral peaks at wavenumbers consistent with the theoretically expected value for mode-1 internal tides. The data are not always consistent with the traveling wave model. Because the spacing of the altimeter tracks is larger than the internal-tide wavelength, the objective map underestimates the energy between the altimeter tracks. With this caveat, the maps are used to determine that 2.6 GW of power is radiated from a 1 700 km section of the Hawaiian Ridge. Time series of hydrographic data obtained at the HOT site north of Oahu, Hawaii show that changes in mode-1 phase speed, caused by variations in stratification, have only a small effect on the propagation of the mode-1 internal tides.