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Caitlin Whalen

Principal Oceanographer

Affiliate Assistant Professor, Oceanography

Email

cwhalen@apl.uw.edu

Phone

206-897-1739

Research Interests

Small-Scale Oceanic Processes: Diapycnal Mixing, Internal Waves, Submesoscale Dynamics, Air–Sea Interactions, and Mesoscale–Internal Wave Interactions

Education

B.A. Physics, Reed College, 2008

Ph.D. Physical Oceanography, University of California at San Diego, 2015

Publications

2000-present and while at APL-UW

Global distribution and governing dynamics of submesoscale density fronts

Whalen, C.B., and K. Drushka, "Global distribution and governing dynamics of submesoscale density fronts," J. Phys. Oceanogr., 55, 1831-1845, doi:10.1175/JPO-D-24-0119.1, 2025.

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1 Oct 2025

While the dynamics at submesoscales (on the order of 0.1–10 km) are thought to be important globally for a range of processes near the air–sea interface, few observational studies sufficiently span scales to include both the submesoscale and global scales, leaving many questions concerning the coupling between the scales unexplored. To address this gap, we use a global dataset of ship-based thermosalinograph and satellite sea surface temperature data to identify over 250 000 submesoscale density fronts throughout the ocean. Globally, we find that the mean submesoscale frontal dynamics can be characterized by a scaling based on the hypothesis that the Rossby number and Froude number are proportional, Ro ∼ Fr. Our results also show that the large-scale ocean characteristics play a role in setting the spatial variability of submesoscale frontal horizontal buoyancy gradients (i.e., frontal "sharpness"). If the large-scale background density gradient is large and/or dominated by salinity as opposed to temperature variability, then submesoscale fronts tend to be sharper. We show that globally, shallow mixed layers are also associated with sharper submesoscale fronts, in contrast to previous regional-scale findings. This global perspective on the variability and dynamics of submesoscale fronts raises many additional questions and, hopefully, will inspire the formation of new scale-spanning avenues for future studies.

Observations of turbulence generated by a near-inertial wave propagating downward in an anticyclonic eddy

Alford, M.H., A. Le Boyer, A.S. Ren, G. Voet, C. Bellerjeau, C.B. Whalen, B. Hall, and N. Cuoto, "Observations of turbulence generated by a near-inertial wave propagating downward in an anticyclonic eddy," Geophys. Res. Lett., 52, doi:DOI10.1029/2024GL114070, 2025.

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28 Mar 2025

Two perpendicular microstructure turbulence and shipboard velocity sections were conducted at high horizontal resolution across an anticyclonic warm core ring. The observations showed elevated turbulence in the core of the eddy, coincident with regions of low Richardson number
(Ri). Shear leading to the low Ri was associated with a downward-propagating near-inertial wave that appeared to be trapped in the negative vorticity associated with the eddy, as has been found previously. The magnitude of the turbulence production agreed well with the vertical divergence of the vertical energy flux of the wave. The mixing coefficient of the turbulence was near 0.2, which together with the correlation with low Ri suggests that shear instability drives the turbulence. A high shear-to-strain ratio of 10.3 was found, as expected for a shear-dominated near-inertial wave. Fine-structure parameterizations using strain only and both shear and strain overestimate the turbulence by factors of 2.7 and 12 respectively.

Coherent float arrays for near-inertial wave studies

Girton, J.B., C.B. Whalen, R.-C. Lien, and E. Kunze, "Coherent float arrays for near-inertial wave studies," Oceanography, 37, 58-67, doi:10.5670/oceanog.2024.306, 2024.

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1 Dec 2024

Rapid changes in winds drive rotating currents known as inertial oscillations. In a stratified ocean, these oscillations can then initiate subsurface near-​inertial internal waves that propagate laterally and vertically and are refracted by horizontal gradients in vorticity. We report on a process study of wind forcing and ocean response in the Iceland Basin of the North Atlantic using arrays of profiling floats measuring temperature, salinity, horizontal velocity, and turbulence. Three arrays with four to eight floats each sampled spatial gradients in both high-frequency (internal wave) and low-frequency (mesoscale) currents in order to clarify the dynamical coupling between these distinct categories of oceanic phenomena.

The observations are qualitatively consistent with theory for wave-​mesoscale interactions: immediately following each wind event, a surface inertial oscillation appears that initially matches a simple slab mixed-layer model in both amplitude and phase, but diverges over several cycles to become a super-inertial internal wave. The surface oscillation decays over several days, while near-inertial energy appears below the surface layer two to three days after the surface motion. Lateral phase gradients estimated from the inertial cycle at each float show that the deeper energy has shorter horizontal wavelengths and tends to propagate toward anticyclonic (negative) vorticity.

These case studies illustrate both the strengths and limitations of Lagrangian (flow-following) arrays for the study of the energetics of air-sea interaction. High-resolution observations of this kind are not feasible globally, but examples in a variety of wind and ocean eddy environments can improve our understanding and verify estimates of wind-energy input and mixing from numerical models and theory.

More Publications

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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