Observations of sound-speed fluctuations on the New Jersey continental shelf in the summer of 2006

Abstract

Environmental sensors moored on the New Jersey continental shelf tracked constant density surfaces (isopycnals) for 35 days in the summer of 2006. Sound-speed fluctuations from internal-wave vertical isopycnal displacements and from temperature/salinity variability along isopycnals (spiciness) are analyzed using frequency spectra and vertical covariance functions. Three varieties of internal waves are studied: Diffuse broadband internal waves (akin to waves fitting the deep water Garrett/Munk spectrum), internal tides, and, to a lesser extent, nonlinear internal waves. These internal-wave contributions are approximately distinct in the frequency domain. It is found that in the main thermocline spicy thermohaline structure dominates the root mean square sound-speed variability, with smaller contributions coming from (in order) nonlinear internal waves, diffuse internal waves, and internal tides. The frequency spectra of internal-wave displacements and of spiciness have similar form, likely due to the advection of variable-spiciness water masses by horizontal internal-wave currents, although there are technical limitations to the observations at high frequency. In the low-frequency, internalwave band the internal-wave spectrum follows frequency to the À1.81 power, whereas the spice spectrum shows a À1.73 power. Mode spectra estimated via covariance methods show that the diffuse internal-wave spectrum has a smaller mode bandwidth than Garrett/Munk and that the internal tide has significant energy in modes one through three.

Observations of sound-speed fluctuations in the western Philippine Sea in the spring of 2009

“…Larger spice variations are expected in the upper ocean where strong spice anomalies are generated by precipitation, evaporation, and wind-forced mixing. The values observed here, however, are much smaller than those observed by Ferrari and Rudnick (2000) in the winter eastern North Pacific Ocean and by Colosi et al (2012) TABLE II. Observed isopycnal statistics for every other tracked isopycnal.…”

“…The techniques for isopycnal and spice analysis utilized in this manuscript were recently presented for a shallow water environment (Colosi et al, 2012). Therefore, the description of the methodology here will be rather terse, and the interested reader should refer to Colosi et al (2012) for more specific details.…”

“…Therefore, the description of the methodology here will be rather terse, and the interested reader should refer to Colosi et al (2012) for more specific details.…”

Modeling and Forecasting Ocean Acoustic Conditions

“…However, making improvements to acoustic system performance prediction poses a strong challenge to ocean modeling capabilities. The reasons include incomplete dynamics in models (such as the absence of explicit, double-diffusive influences on intrusions known to affect sound (Colosi et al 2012a;Duda and Sellers 2016)), insufficient resolution of the dynamical models, and insufficient data to constrain data-driven models in the absence of special regional focus. Data-constrained modeling is now routine (Edwards et al 2015).…”

Low-frequency broadband sound source localization using an adaptive normal mode back-propagation approach in a shallow-water ocean

“…They reveal the complicated frontal variability known at this location, including the foot of the front, frontal intrusions in the middle of the water column and internal waves and tides. Each of these features can cause sound speed variability, and a paper by Colosi et al (2012) is referred to for detailed discussions. The barotropic tides, shown in Fig.…”