About this project
Understanding along-isopycnal variability of temperature to better understand how submesoscale features affect sound propagation across the spicy ocean.
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)
Ballard et al. (2026)
In the Nordic Seas, Atlantic- and Arctic-origin waters collide, and the resulting hydrographic variability doesn’t just reshape the water column — it reshapes sound. During the 2022 Northern Ocean Rapid Surface Evolution experiment, internal tides and an anticyclonic eddy pushed the Atlantic Water layer around enough to measurably shift the region’s natural sound channel, altering how acoustic arrivals show up at a receiver. It’s a direct link between mesoscale hydrography and acoustic predictability in a basin where both are hard to pin down.
(Ballard et al., 2026)
References
2026
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Hydrographic Variability and Sound-Channel Dynamics in the Nordic Seas: Implications for Predicting Acoustic Arrival Structure
Megan S. Ballard, Alejandra Sanchez-Rios, Robert T. Taylor, and 9 more authors
Journal of Geophysical Research: Oceans, Jun 2026
Atlantic and Arctic-origin waters converge in the Nordic Seas, creating variability that affects both hydrography and sound propagation. High-resolution measurements collected during the 2022 Northern Ocean Rapid Surface Evolution experiment, using shipboard systems and acoustic transmissions, show that internal tides and an anticyclonic eddy were the dominant features producing measurable shifts in the Atlantic Water layer that functions as a regional sound channel. These hydrographic changes altered acoustic arrival patterns, with implications for acoustic observing and Arctic basin research.
2023
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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.