The internal tide of the western North Atlantic observed using long‐range reciprocal acoustic transmissions

Time series of ray travel times were obtained at 350‐, 410‐, and 670‐km ranges in the western North Atlantic during the 1991–2 Acoustic Mid‐Ocean Dynamics Experiment (AMODE). Transmissions were recorded for approximately 300 days between six transceivers in a pentagonal array. Sound‐speed variability is separated from current variability by calculating the sum of reciprocal travel times. Both phase‐locked and narrow‐band internal‐tide sound‐speed variability, caused by the internal‐tide isotach displacement, are observed by the sum travel times. The description of the acoustic array as a high‐directivity antenna for the incident internal tide will be given. Beamforming the internal tide M2 and K1 harmonic constants determined on each of the 15 acoustic paths suggests two origins of significant internal tide generation are the Blake Escarpment and the continental shelf north of Puerto Rico. The nontidal, high‐frequency variability (≳1 cpd) is due to internal‐wave sound‐speed and current variability.