Barotropic currents, vorticity, and tides in the northcentral Pacific in summer 1987 determined from long‐range acoustic transmissions Free

Large‐scale depth‐integrated currents, relative vorticity, and tides were measured in the northcentral Pacific Ocean during summer 1987 using long‐range reciprocal acoustic transmissions between transceivers in a triangle approximately 1000 km on a side. Tidal harmonic constants found from the acoustically determined currents agree with those found from current meters and with the tidal models of Schwiderski [E. W. Schwiderski, Mar. Geod. 3, 161–255 (1980)] and Cartwright et al. [D. E. Cartwright et al., NASA Tech. Mem. 104578 (1992)]. Sum travel times were used to calculate the baroclinic tide isotach displacement. A significant part of the derived internal tide is deterministic. Currents are calculated using the topographic Sverdrup balance with the Fleet Numerical Oceanography Center wind field. The measured time derivative of the areal‐averaged relative vorticity is insignificant to the Sverdrup balance. Currents and vorticity calculated using the Sverdrup balance are an order of magnitude smaller than the observations. The magnitude and variability of the large‐scale currents and vorticity determined from the Semtner–Chervin eddy‐resolving model of ocean circulation [A. J. Semtner and R. M. Chervin, J. Geophys. Res. 93, 15 502–15 522 (1988)] are similar to the direct measurements. [Work supported by NSF and ONR.]