BAROTROPIC AND BAROCLINIC TIDES IN THE CENTRAL NORTH PACIFIC-OCEAN DETERMINED FROM LONG-RANGE RECIPROCAL ACOUSTIC TRANSMISSIONS

Travel times of reciprocal 1000-km range acoustic transmissions, deter mined from the 1987 Reciprocal Tomography Experiment, are used to stud y barotropic tidal currents and a large-scale, coherent baroclinic tid e in the central North Pacific Ocean. The difference in reciprocal tra vel times determines the tidal currents, while the sum of reciprocal t ravel times determines the baroclinic tide displacement of isotachs (o r equivalently, isotherms). The barotropic tidal current accounts for 90% of the observed differential travel time variance. The measured ha rmonic constants of the eight major tidal constituents of the barotrop ic tide and the constants determined from current meter measurements a gree well with the empirical-numerical tidal models of Schwiderski and Cartwright et al. The amplitudes and phases of the first-mode barocli nic tide determined from sum travel times agree with those determined from moored thermistors and current meters. The baroclinic tidal signa ls are consistent with a large-scale, phase-locked internal tide, whic h apparently has propagated northward over 2000 km from the Hawaiian R idge. The amplitude, phase, and polarization of the first-mode M(2) ba roclinic tidal displacement and current are consistent with a northwar d propagating internal tide. The ratio of baroclinic energy to barotro pic energy determined using the range-averaging acoustic transmissions is about 8%, while a ratio of 26% was determined from the point measu rements. The large-scale, internal tide energy flux, presumed northwar d, is estimated to be about 180 W m(-1).