Tidal signals in basin-scale acoustic transmissions

Abstract

Travel times of acoustic signals were measured between a bottom-mounted source near Oahu and five bottom-mounted receivers located near Washington, Oregon, and California in 1988 and 1989. This paper discusses the observed tidal signals. At three out of five receivers, observed travel times at M2 and S2 periods agree with predictions from a barotropic tide model to within ±30° in phase and a factor of 1.6 in amplitude. The discrepancies at the fourth and fifth receivers can largely be accounted for with a simple model for the generation of baroclinic tides by interactions between the barotropic tides and guyots in the Moonless mountains. These baroclinic tides are phase locked to the astronomical tide-generating forces. A simple model is used to estimate the conversion of energy from barotropic to baroclinic tides by the world’s seamounts. At M2, the conversion amounts to about 1×1018 erg s−1, or about 4% of the total dissipation at M2. Although this estimate is very approximate, it is similar to other published values.