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James Girton

Principal Oceanographer

Affiliate Assistant Professor, Oceanography

Email

girton@uw.edu

Phone

206-543-8467

Research Interests

Overflows and Deep-Water Formation, Internal Waves, Mesoscale Eddies, Oceanic Surface and Bottom Boundary Layers, Measurements of Ocean Velocity Through Motionally-Induced Voltages

Biosketch

James Girton's research primarily investigates ocean processes involving small-scale turbulence and mixing and their influence on larger-scale flows. An important part of physical oceanography is the collection of novel datasets to shed new light on important physical processes, and to this end Dr. Girton's research has frequently drawn upon the widely under-utilized electromagnetic velocity profiling technique developed by Tom Sanford (his Ph.D. advisor and frequent collaborator). Instruments utilizing this technique include the expendable XCP, the full-depth free-falling AVP, and the autonomous long-duration EM-APEX. Each of these instruments has a unique role to play in the study of phenomena ranging from deep boundary currents and overflows to upper ocean mixing and internal waves.

In addition to being less well-understood elements of ocean physics, many of these phenomena are potentially important for the behavior of the large-scale ocean circulation, particularly the meridional overturning that transports heat to subpolar and polar regions and sequesters atmospheric gases in the deep ocean. Prediction of future climate change by coupled ocean-atmosphere models requires reliable predictions of ocean circulation, so physically-based improvements to parameterizations of mixing, boundary stresses and internal waves in such models are an ongoing goal.

Department Affiliation

Ocean Physics

Education

B.A. Physics, Swarthmore College, 1993

Ph.D. Oceanography, University of Washington, 2001

Projects

Sampling QUantitative Internal-wave Distributions — SQUID

Our goals are to understand the generation, propagation, and dissipation mechanisms for oceanic internal gravity waves to enable seamless, skillful modeling & forecasts of these internal waves between the deep ocean and the shore.

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26 Feb 2024

The SQUID team will provide a globally distributed observing program for shear, energy flux, and mixing by internal waves. We will use profiling floats — measuring temperature, salinity, velocity, and turbulence — that will yield new insights into internal wave regimes and parameterizations, and that will provide direct and derived data products tailored for use by modeling groups for comparison and validation.

Wave Glider Observations in the Southern Ocean

A Wave Glider autonomous surface vehicle will conduct a summer-season experiment to investigate ocean–shelf exchange on the West Antarctic Peninsula and frontal air–sea interaction over both the continental shelf and open ocean.

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4 Sep 2019

Southern Ocean climate change is at the heart of the ocean's response to anthropogenic forcing. Variations in South Polar atmospheric circulation patterns, fluctuations in the strength and position of the Antarctic Circumpolar Current, and the intertwining intermediate deep water cells of the oceanic meridional overturning circulation have important impacts on the rate of ocean carbon sequestration, biological productivity, and the transport of heat to the melting continental ice shelves.

Submesoscale Mixed-Layer Dynamics at a Mid-Latitude Oceanic Front

SMILE: the Submesoscale MIxed-Layer Eddies experiment

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1 Mar 2017

This experiment is aimed at increasing our understanding of the role of lateral processes in mixed-layer dynamics through a series of ship surveys and Lagrangian array deployments. Instrument deployments and surveys target the upper ocean's adjustment to winter atmospheric forcing events in the North Pacific subtropical front, roughly 800 km north of Hawaii.

This study will improve understanding of 1–10-km scale lateral processes in three-dimensional mixed-layer dynamics in a region of above-average atmospheric forcing, typical mid-ocean mesoscale advection and straining, and typical submesoscale activity. The results will improve the physical basis of mixed-layer parameterizations, leading to better model predictions of air-sea fluxes, gas transfer, and biological productivity.

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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.

Mixing and water mass transformation over Discovery Bank, in the Weddell–Scotia confluence of the Southern Ocean

Brearley, J.A., and 7 others including J.B. Girton, "Mixing and water mass transformation over Discovery Bank, in the Weddell–Scotia confluence of the Southern Ocean," J. Geophysical. Res., 129, doi:10.1029/2023JC020610, 2024.

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19 Sep 2024

The South Scotia Ridge, in the Atlantic sector of the Southern Ocean, is a key region for water mass modification. It is the location of the Weddell–Scotia Confluence, an area of reduced stratification which separates the Weddell Gyre to the south and the Antarctic Circumpolar Current to the north, and which receives input of shelf waters from the tip of the Antarctic Peninsula. To elucidate the transformations over the ridge, we focus on one of its largest seamounts, Discovery Bank, which has previously been observed as hosting a stratified Taylor column that retains water for months to years, during which time water masses are entrained from north and south of the Weddell Front and steadily mixed. Data from ship-deployed sensors and autonomous platforms are analyzed to quantify and understand the diapycnal mixing, heat fluxes and water mass transformations over the bank. Ocean glider and free-profiling drifting float data show that the mid-depth temperature maximum of the Circumpolar Deep Water (CDW) is eroded between the northern and southern sides of the bank, while diapycnal diffusivity is enhanced by up to an order-of-magnitude over its steeply sloping portions. This is accompanied by heat fluxes from the CDW layer being increased by up to a factor of six, which may contribute to a reduction in mid-depth stratification. Tidal model analysis shows that the southern side of the bank hosts strong barotropic to baroclinic energy conversion (>150 N m-2), emphasizing the role of internal tides in modulating water mass transformations in the Confluence.

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In The News

Fact check: Video shows 'bono wave' tidal bore, not HAARP-generated phenomena

USA Today, Eleanor McCrary

A viral video shared on social media shows a naturally occurring tidal bore on the Kampar River in Indonesia. James Girton serves as one of the fact-check sources.

11 Apr 2023

UW team sending autonomous surfboard to explore Antarctic waters

UW News, Hannah Hickey

The research project will use the Wave Glider to investigate the summer conditions near Palmer Station on the Antarctic Peninsula, to better understand how the warming ocean interacts with ice shelves that protrude from the shore. It will then head across Drake Passage, braving some of the stormiest seas on the planet.

23 Oct 2019

One year into the mission, autonomous ocean robots set a record in survey of Antarctic ice shelf

UW News, Hannah Hickey

A team of ocean robots deployed in January 2018 have, over the past year, been the first self-guided ocean robots to successfully travel under an ice sheet and return to report long-term observations.

23 Jan 2019

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