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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

A generalized slab model

Stokes, I.A., S.M. Kelly, A.J. Lucas, A.F. Waterhouse, C.B. Whalen, T. Klenz, V. Hormann, and L. Centurioni, "A generalized slab model," J. Phys. Oceanogr., 54, 949-965, doi:10.1175/JPO-D-23-0167.1, 2024.

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17 Jan 2024

We construct a generalized slab model to calculate the ocean’s linear response to an arbitrary, depth-variable forcing stress profile. To introduce a first-order improvement to the linear stress profile of the traditional slab model, a nonlinear stress profile which allows momentum to penetrate into the transition layer (TL) is used (denoted 'mixed layer/transition layer,' or MLTL stress profile). The MLTL stress profile induces a two-fold reduction in power input to inertial motions relative to the traditional slab approximation. The primary reduction arises as the TL allows momentum to be deposited over a greater depth range, reducing surface currents. The secondary reduction results from the production of turbulent kinetic energy (TKE) beneath the mixed layer (ML) related to interactions between shear stress and velocity shear. Direct comparison between observations in the Iceland Basin, the traditional slab model, the generalized slab model with the MLTL stress profile, and the Price-Weller-Pinkel (PWP) model suggest that the generalized slab model offers improved performance over a traditional slab model. In the Iceland Basin, modeled TKE production in the TL is consistent with observations of turbulent dissipation. Extension to global results via analysis of Argo profiling float data suggests that on the global, annual-mean, ~30% of the total power input to near-inertial motions is allocated to TKE production. We apply this result to the latest global, annual-mean estimates for near-inertial power input (0.27 TW) to estimate that 0.08 ± 0.01 TW of the total near-inertial power input are diverted to TKE production.

Seasonal variability of near-inertial/semidiurnal fluctuations and turbulence in the subarctic North Atlantic

Kunze, E., R.-C. Lien, C.B. Whalen, J.B. Girton, B. Ma, and M.C. Buijsman, "Seasonal variability of near-inertial/semidiurnal fluctuations and turbulence in the subarctic North Atlantic," J. Phys. Oceanogr., 53, 2717-2735, doi:10.1175/JPO-D-22-0231.1, 2023.

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1 Dec 2023

Six profiling floats measured water-mass properties (Т, S), horizontal velocities (u, v) and microstructure thermal-variance dissipation rates χT in the upper ~1 km of Iceland and Irminger Basins in the eastern sub-polar North Atlantic from June 2019 to April 2021. The floats drifted into slope boundary currents to travel counterclockwise around the basins. Pairs of velocity profiles half an inertial period apart were collected every 7–14 days. These half-inertial-period pairs are separated into subinertial eddy (sum) and inertial/semidiurnal (difference) motions. Eddy flow speeds are ~O(0.1 m s-1) in the upper 400 m, diminishing to ~O(0.01 m s-1) by ~800-m depth. In late summer through early spring, near-inertial motions are energized in the surface layer and permanent pycnocline to at least 800-m depth almost simultaneously (within the 14-day temporal resolution), suggesting rapid transformation of large-horizontal-scale surface-layer inertial oscillations into near-inertial internal waves with high vertical group velocities through interactions with eddy vorticity-gradients (effective β). During the same period, internal-wave vertical shear variance was 2–5 times canonical midlatitude magnitudes and dominantly clockwise-with-depth (downward energy propagation). In late spring and early summer, shear levels are comparable to canonical midlatitude values and dominantly counterclockwise-with-depth (upward energy propagation), particularly over major topographic ridges. Turbulent diapycnal diffusivities K ~O(10-4 m2 s-1) are an order of magnitude larger than canonical mid-latitude values. Depth-averaged (10–1000 m) diffusivities exhibit factor-of-three month-by-month variability with minima in early August.

Significance of diapycnal mixing within the Atlantic Meridional Overturning Circulation

Cimoli, L., and 10 others including C.B. Whalen, "Significance of diapycnal mixing within the Atlantic Meridional Overturning Circulation," AGU Adv., 4, doi:10.1029/2022AV000800, 2023.

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1 Apr 2023

Diapycnal mixing shapes the distribution of climatically important tracers, such as heat and carbon, as these are carried by dense water masses in the ocean interior. Here, we analyze a suite of observation-based estimates of diapycnal mixing to assess its role within the Atlantic Meridional Overturning Circulation (AMOC). The rate of water mass transformation in the Atlantic Ocean's interior shows that there is a robust buoyancy increase in the North Atlantic Deep Water (NADW, neutral density ≅ 27.6–28.15), with a diapycnal circulation of 0.5–8 Sv between 48°N and 32°S in the Atlantic Ocean. Moreover, tracers within the southward-flowing NADW may undergo a substantial diapycnal transfer, equivalent to a vertical displacement of hundreds of meters in the vertical. This result, confirmed with a zonally averaged numerical model of the AMOC, indicates that mixing can alter where tracers upwell in the Southern Ocean, ultimately affecting their global pathways and ventilation timescales. These results point to the need for a realistic mixing representation in climate models in order to understand and credibly project the ongoing climate change.

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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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