title: Observations of sound-speed fluctuations in the western Philippine Sea in the spring of 2009.
abstract: 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.
authors.affiliation: Department of Oceanography, Naval Postgraduate School, Monterey, California 93943.
authors.forename: John A
authors.initials: JA
authors.lastname: Colosi
authors.forename: Lora J
authors.initials: LJ
authors.lastname: Van Uffelen
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Cornuelle
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Dzieciuch
authors.forename: Peter F
authors.initials: PF
authors.lastname: Worcester
authors.forename: Brian D
authors.initials: BD
authors.lastname: Dushaw
authors.forename: Steven R
authors.initials: SR
authors.lastname: Ramp
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D015233:Models, Statistical; D009038:Motion; D009791:Oceanography / Q000295:instrumentation / Q000379:methods*; D009792:Oceans and Seas; D010679:Philippines; D012621:Seasons; D012623:Seawater; D012815:Signal Processing, Computer-Assisted; D059629:Signal-To-Noise Ratio; D013016:Sound; D013018:Sound Spectrography; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014159:Transducers