Barotropic and Baroclinic Tides in the Central North Pacific Ocean Determined from Long-Range Reciprocal Acoustic Transmissions

Abstract

Abstract Travel times of reciprocal 1000-km range acoustic transmissions, determined from the 1987 Reciprocal Tomography Experiment, are used to study barotropic tidal currents and a large-scale, coherent baroclinic tide in the central North Pacific Ocean. The difference in reciprocal travel times determines the tidal currents, while the sum of reciprocal travel times determines the baroclinic tide displacement of isotachs (or equivalently, isotherms). The barotropic tidal current accounts for 90% of the observed differential travel time variance. The measured harmonic constants of the eight major tidal constituents of the barotropic tide and the constants determined from current meter measurements agree well with the empirical–numerical tidal models of Schwiderski and Cartwright et al. The amplitudes and phases of the first-mode baroclinic tide determined from sum travel times agree with those determined from moored thermistors and current meters. The baroclinic tidal signals are consistent with a large-...