Basin-scale tidal measurements using acoustic tomography

Abstract

Travel-times of acoustic signals were measured between a bottom-mounted source near Oahu and four bottom-mounted receivers located near Washington, Oregon, and California in 1988 and 1989. This paper discusses the observed tidal signals. At three out of four receivers, observed travel times at M2 and S2 periods agree with predictions from barotropic tide models to within ±30° in phase and a factor of 1.6 in amplitude. The discrepancy at the fourth receiver can be removed by including predicted effects of phase-locked baroclinic tides generated by seamounts. Our estimates of barotropic M2 tidal dissipation by seamounts vary between 2 x 1016 and 1 X 1018 erg·s-1. The variation by two orders of magnitude is due to uncertainties in the numbers and sizes of seamounts. The larger dissipation (1 x 1018 erg·s-1) is the same order as previous estimates and amounts to 4% of the total dissipation at M2.