About this project
Understanding along-isopycnal variability of temperature to better understand how submesoscale features affect sound propagation across the spicy ocean.
Sanchez-Rios et al. (2024)
When the Kuroshio advects warm, salty Pacific water into the fresher South China Sea, it doesn’t mix quietly — it laminates. Layer by layer, contrasting water masses interleave like pages in a book, creating a staircase of temperature and salinity that defies standard mixing recipes. We followed these interleavings with gliders, wirewalkers and microstructure profilers and found that where salt fingers and shear instability coincide, turbulent mixing runs an order of magnitude larger than predicted.. ci
(Sanchez-Rios et al., 2024)
Ballard et al. (2023)
Sound doesn’t always travel in straight lines. In the Jan Mayen Channel, connecting the Greenland and Norwegian Seas, we recorded acoustic arrivals that had bent nearly 180° — not from a single reflection, but from repeated seafloor bounces that steered the signal back toward its source. Drifting hydrophones caught the geometry in the act, and a 3D ray trace revealed the mechanism: horizontal refraction, hiding in plain sight in a canyon most models treat as a wall.
(Ballard et al., 2023)
References
2024
-
Characterization of Mixing at the Edge of a Kuroshio Intrusion into the South China Sea: Analysis of Thermal Variance Diffusivity Measurements
Alejandra Sanchez-Rios, R. Kipp Shearman, Craig M. Lee, and 5 more authors
May 2024
The Kuroshio occasionally carries warm and salty North Pacific Water into fresher waters of the South China Sea, forming a front with a complex temperature–salinity (T–S) structure to the west of the Luzon Strait. In this study, we examine the T–S interleavings formed by alternating layers of North Pacific Water with South China Sea Water in a front formed during the winter monsoon season of 2014. Using observations from a glider array following a free-floating wave-powered vertical profiling float to calculate the fine-scale parameters Turner angle, Tu, and Richardson number, Ri, we identified areas favorable to double-diffusion convection and shear instability observed in a T–S interleaving. We evaluated the contribution of double-diffusion convection and shear instabilities to the thermal variance diffusivity, χ, using microstructure data and compared it with previous parameterization schemes based on fine-scale properties. We discover that turbulent mixing is not accurately parameterized when both Tu and Ri are within critical ranges (Tu > 60; Ri < \frac14). In particular, χ associated with salt finger processes was an order of magnitude higher (6.7 \texttimes 10-7 K2 s-1) than in regions where only velocity shear was likely to drive mixing (8.7 \texttimes 10-8 K2 s-1).
2023
-
Out-of-Plane Arrivals Recorded by Drifting Hydrophones during the Northern Ocean Rapid Surface Evolution Experiment
Megan S. Ballard, Jason D. Sagers, Pierre-Marie Poulain, and 3 more authors
The Journal of the Acoustical Society of America, Nov 2023
This paper reports on an observation of three-dimensional (3D) arrivals for which the change in the direction of horizontally refracted sound is nearly 180^∘. The experimental site is Jan Mayen Channel (JMCh), which connects the Greenland and Norwegian Seas. During the experiment, signals from a moored source transmitting a 500–1500 Hz sweep every 4 h were recorded by three surface drifters equipped with hydrophone arrays. Over a 3-day period, the drifters moved north across JMCh toward the moored source. In each recording, an in-plane arrival is identified. In a subset of these recordings, a second arrival is observed, having travel time consistent with propagation from the moored source, turning at the ridge on the south side of the channel, and arriving at the drifters. In a smaller subset of recordings, a third arrival is also observed having travel time consistent with a turning point on the face of the bathymetric rise on the west end of the channel that forms the Jan Mayen volcano. A 3D ray trace is employed to show the change in direction results from repeated reflections from the seafloor such that it is classified as horizontal refraction and not a single-bounce reflection.