Publications

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2005
Andrew, RK, Howe BM, Mercer JA, Group NPAL, Cornuelle B, Colosi J.  2005.  Transverse horizontal spatial coherence of deep arrivals at megameter ranges. Journal of the Acoustical Society of America. 117:1511-1526.   10.1121/1.1854851   AbstractWebsite

Predictions of transverse horizontal spatial coherence from path integral theory are compared with measurements for two ranges between 2000 and 3000 km. The measurements derive from a low-frequency (75 Hz) bottom-mounted source at depth 810 m near Kauai that transmitted m-sequence signals over several years to two bottom-mounted horizontal line arrays in the North Pacific. In this paper we consider the early arriving portion of the deep acoustic field at these arrays. Horizontal coherence length estimates, on the order of 400 m, show good agreement with lengths calculated from theory. These lengths correspond to about 1 degrees in horizontal arrival angle variability using a simple, extended, spatially incoherent source model, Estimates of scintillation index, log-amplitude variance, and decibel intensity variance indicate that the fields were partially saturated. There was no significant seasonal variability in these measures. The scintillation index predictions agree quite well with the dataset estimates; nevertheless, the scattering regime predictions (fully saturated) vary from the regime classification (partially saturated) inferred from observation. This contradictory result suggests that a fuller characterization of scattering regime metrics may be required. (c) 2005 Acoustical Society of America.

1995
Dushaw, BD, Cornuelle BD, Worcester PF, Howe BM, Luther DS.  1995.  Barotropic and Baroclinic Tides in the Central North Pacific-Ocean Determined from Long-Range Reciprocal Acoustic Transmissions. Journal of Physical Oceanography. 25:631-647.   10.1175/1520-0485(1995)025<0631:babtit>2.0.co;2   AbstractWebsite

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-scale, phase-locked internal tide, which apparently has propagated northward over 2000 km from the Hawaiian Ridge. The amplitude, phase, and polarization of the first-mode M(2) baroclinic tidal displacement and current are consistent with a northward propagating internal tide. The ratio of baroclinic energy to barotropic energy determined using the range-averaging acoustic transmissions is about 8%, while a ratio of 26% was determined from the point measurements. The large-scale, internal tide energy flux, presumed northward, is estimated to be about 180 W m(-1).

1994
Dushaw, BD, Worcester PF, Cornuelle BD, Howe BM.  1994.  Barotropic Currents and Vorticity in the Central North Pacific-Ocean During Summer 1987 Determined from Long-Range Reciprocal Acoustic Transmissions. Journal of Geophysical Research-Oceans. 99:3263-3272.   10.1029/93jc03335   AbstractWebsite

Large-scale depth-integrated currents and relative vorticity were measured in the central North Pacific Ocean during summer 1987 using long-range reciprocal acoustic transmissions between transceivers in a triangle approximately 1000 km on a side. Inverse techniques were used to estimate the depth-averaged (barotropic) current bihourly at 4-day intervals from differential travel times. Tidal constituent amplitudes and phases found from the acoustically determined currents agree with those found from current meters and with the tidal models of Schwiderski (1980) and Cartwright et al. (1992), providing confirmation that the tomographically derived barotropic currents are correct within the expected uncertainties. The estimated low-frequency, large-scale currents are compared with depth-averaged currents determined by point measurements using current meters and bottom-mounted electrometers. Meridional and zonal currents are calculated using the topographic Sverdrup balance with the Fleet Numerical Oceanography Center wind field. The measured time derivative of the areally averaged relative vorticity is shown to be 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 and Chervin (1988) eddy-resolving model of ocean circulation are similar to the direct measurements.

1993
Dushaw, BD, Worcester PF, Cornuelle BD, Howe BM.  1993.  Variability of Heat-Content in the Central North Pacific in Summer 1987 Determined from Long-Range Acoustic Transmissions. Journal of Physical Oceanography. 23:2650-2666.   10.1175/1520-0485(1993)023<2650:vohcit>2.0.co;2   AbstractWebsite

The evolution of the heat content in the central North Pacific Ocean during summer 1987 has been measured using acoustic transmissions between transceivers deployed in a triangle approximately 1000 km on a side. The acoustically determined heat contents of the source-receiver sections agree with heat contents computed from CTD and XBT data obtained during May and September 1987. The accuracy of acoustical measurements of range-averaged heat content is comparable to estimates from CTD and XBT data. Transmissions at four-day intervals allow the continuous observation of heat content and show that it varies on time scales of weeks or less. The magnitude of these variations is of the same order as that observed from XBT sections, which are only occasionally available. Ocean-atmosphere heat exchange from bulk formulas accounts for only about half of the observed heat content increase from May through September 1987, indicating that advective effects are important in the region. The excess heat change is calculated to be of order 50-150 W m(-2). The advective component of the near-surface heat budget is roughly in phase with the surface flux component.