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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 as viewed from global and regional scales including 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

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.

Near-inertial energy variability in a strong mesoscale eddy field in the Iceland Basin

Voet, G., and 13 others including H.L. Simmons, C.B. Whalen, R.-C. Lien, and J.B. Girton, "Near-inertial energy variability in a strong mesoscale eddy field in the Iceland Basin," Oceanography, 37, 34-47, doi:10.5670/oceanog.2024.302, 2024.

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1 Dec 2024

An 18-month deployment of moored sensors in Iceland Basin allows characterization of near-inertial (frequencies near the Coriolis frequency f with periods of ~14 h) internal gravity wave generation and propagation in a region with an active mesoscale eddy field and strong seasonal wind and heat forcing. The seasonal cycle in surface forcing deepens the mixed layer in winter and controls excitation of near-​inertial energy. The mesoscale eddy field modulates near-inertial wave temporal, horizontal, and vertical scales, as well as propagation out of the surface layer into the deep permanent pycnocline. Wind-forced near-inertial energy has the most active downward propagation within anticyclonic eddies. As oceanic surface and bottom boundaries act to naturally confine the propagation of internal waves, the vertical distribution of these waves can be decomposed into a set of "standing" vertical modes that each propagate horizontally at different speeds. The lowest modes, which propagate quickly away from their generation sites, are most enhanced when the mixed layer is deep and are generally directed southward.

Interacting internal waves explain global patterns of interior ocean mixing

Dematteis, G., A. Le Boyer, F. Pollmann, K.L. Polzin, M.H. Alford, C.B. Whalen, and Y.V. Lvov, "Interacting internal waves explain global patterns of interior ocean mixing," Nat. Commun., 15, doi:10.1038/s41467-024-51503-6, 2024.

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29 Aug 2024

Across the stable density stratification of the abyssal ocean, deep dense water is slowly propelled upward by sustained, though irregular, turbulent mixing. The resulting mean upwelling determines large-scale oceanic circulation properties like heat and carbon transport. In the ocean interior, this turbulent mixing is caused mainly by breaking internal waves: generated predominantly by winds and tides, these waves interact nonlinearly, transferring energy downscale, and finally become unstable, break and mix the water column. This paradigm, long parameterized heuristically, still lacks full theoretical explanation. Here, we close this gap using wave-wave interaction theory with input from both localized and global observations. We find near-ubiquitous agreement between first-principle predictions and observed mixing patterns in the global ocean interior. Our findings lay the foundations for a wave-driven mixing parameterization for ocean general circulation models that is entirely physics-based, which is key to reliably represent future climate states that could differ substantially from today's.

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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