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Colosi, JA, Van Uffelen LJ, Cornuelle BD, Dzieciuch MA, Worcester PF, Dushaw BD, Ramp SR.  2013.  Observations of sound-speed fluctuations in the western Philippine Sea in the spring of 2009. Journal of the Acoustical Society of America. 134:3185-3200.   10.1121/1.4818784   AbstractWebsite

As an aid to understanding long-range acoustic propagation in the Philippine Sea, statistical and phenomenological descriptions of sound-speed variations were developed. Two moorings of oceanographic sensors located in the western Philippine Sea in the spring of 2009 were used to track constant potential-density surfaces (isopycnals) and constant potential-temperature surfaces (isotherms) in the depth range 120-2000 m. The vertical displacements of these surfaces are used to estimate sound-speed fluctuations from internal waves, while temperature/salinity variability along isopycnals are used to estimate sound-speed fluctuations from intrusive structure often termed spice. Frequency spectra and vertical covariance functions are used to describe the space-time scales of the displacements and spiciness. Internal-wave contributions from diurnal and semi-diurnal internal tides and the diffuse internal-wave field [related to the Garrett-Munk (GM) spectrum] are found to dominate the sound-speed variability. Spice fluctuations are weak in comparison. The internal wave and spice frequency spectra have similar form in the upper ocean but are markedly different below 170-m depth. Diffuse internal-wave mode spectra show a form similar to the GM model, while internal-tide mode spectra scale as mode number to the minus two power. Spice decorrelates rapidly with depth, with a typical correlation scale of tens of meters.

Tiemann, CO, Worcester PF, Cornuelle BD.  2001.  Acoustic scattering by internal solitary waves in the Strait of Gibraltar. Journal of the Acoustical Society of America. 109:143-154.   10.1121/1.1329624   AbstractWebsite

High-freqnency underwater acoustic transmissions across the Strait of Gibraltar were used to examine acoustic scattering caused by the unique internal wave field in the Strait. Internal solitary waves of 100 m in amplitude propagate along the interface between an upper layer of Atlantic water and a lower layer of Mediterranean water. The interface is also strongly modulated by internal tides of comparable amplitude. As internal solitary waves cross the acoustic path, they cause sharp soundspeed gradients which intermittently refract acoustic rays away from normal sound channels. Internal tides vertically shift soundspeed profiles for additional travel time variability. Although the acoustic scattering is quite complicated, it is also surprisingly robust, making it a good candidate for modeling. Key features of the acoustic arrival pattern can be accounted for in some detail by a model description of the complex hydraulics in the Strait. (C) 2001 Acoustical Society of America. [DOI: 10.1121/1.1329624].

Dushaw, BD, Egbert GD, Worcester PF, Cornuelle BD, Howe BM, Metzger K.  1997.  A TOPEX/POSEIDON global tidal model (TPXO.2) and barotropic tidal currents determined from long-range acoustic transmissions. Progress in Oceanography. 40:337-367.   10.1016/s0079-6611(98)00008-1   AbstractWebsite

Tidal currents derived from the TPXO.2 global tidal model of Egbert, Bennett, and Foreman are compared with those determined from long-range reciprocal acoustic transmissions. Amplitudes and phases of tidal constituents in the western North Atlantic are derived from acoustic data obtained in 1991-1992 using a pentagonal array of transceivers. Small, spatially coherent differences between the measured and modeled tidal harmonic constants mostly result from smoothing assumptions made in the model and errors caused in the model currents by complicated topography to the southwest of the acoustical array. Acoustically measured harmonic constants (amplitude, phase) of M-2 tidal vorticity (3-8 x 10(-9) s(-1), 210-310 degrees) agree with those derived from the TPXO.2 model (2-5 x 10(-9) s(-1), 250-300 degrees), whereas harmonic constants of about (1-2 x 10(-9) s(-1), 350-360 degrees) are theoretically expected from the equations of motion. Harmonic constants in the North Pacific Ocean are determined using acoustic data from a triangular transceiver array deployed in 1987. These constants are consistent with those given by the TPXO.2 tidal model within the uncertainties. Tidal current harmonic constants determined from current meters do not generally provide a critical test of tidal models. The tidal currents have been estimated to high accuracy using long-range reciprocal acoustic transmissions; these estimates will be useful constraints on future global tidal models. (C) 1998 Elsevier Science Ltd. All rights reserved.