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James Girton

Principal Oceanographer

Affiliate Assistant Professor, Oceanography

Email

girton@apl.washington.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

Publications

2000-present and while at APL-UW

Sustained measurements of Southern Ocean air–sea coupling from a Wave Glider autonomous surface vehicle

Thomson, J., and J. Girton, "Sustained measurements of Southern Ocean air–sea coupling from a Wave Glider autonomous surface vehicle," Oceanography, 30, 104-109, doi:10.5670/oceanog.2017.228, 2017.

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1 Jun 2017

The four-month mission of a Wave Glider in the Southern Ocean has demonstrated the capability for an autonomous surface vehicle to make sustained measurements of air-sea interactions in remote regions. Several new sensor payloads were integrated for this mission, including a three-axis sonic anemometer for turbulent wind stress estimation and a high-resolution atmospheric pressure gage. The mission focused on Drake Passage, where strong gradients are common along the Antarctic Circumpolar Current (ACC) fronts. Using satellite data products, pilots ashore were able to remotely navigate the Wave Glider across the ACC Polar Front and measure changes in air-sea coupling. The resulting data set combines the persistence of a mooring with the adaptability of a ship-based survey.

Observations of a large lee wave in the Drake Passage

Cusack, J.M., A.C. Naveira Garabato, D.A. Smeed, and J.B. Girton, "Observations of a large lee wave in the Drake Passage," J. Phys. Oceanogr., 47, 793-810, doi:10.1175/JPO-D-16-0153.1, 2017.

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1 Apr 2017

Lee waves are thought to play a prominent role in Southern Ocean dynamics, facilitating a transfer of energy from the jets of the Antarctic Circumpolar Current to microscale, turbulent motions important in water mass transformations. Two EM-APEX profiling floats deployed in the Drake Passage during the Diapycnal and Isopycnal Mixing Experiment (DIMES) independently measured a 120 ± 20-m vertical amplitude lee wave over the Shackleton Fracture Zone. A model for steady EM-APEX motion is developed to calculate absolute vertical water velocity, augmenting the horizontal velocity measurements made by the floats. The wave exhibits fluctuations in all three velocity components of over 15 cm s-1 and an intrinsic frequency close to the local buoyancy frequency. The wave is observed to transport energy and horizontal momentum vertically at respective peak rates of 1.3 ± 0.2 W m-2 and 8 ± 1 N m-2. The rate of turbulent kinetic energy dissipation is estimated using both Thorpe scales and a method that isolates high-frequency vertical kinetic energy and is found to be enhanced within the wave to values of order 10-7 W kg-1. The observed vertical flux of energy is significantly larger than expected from idealized numerical simulations and also larger than observed depth-integrated dissipation rates. These results provide the first unambiguous observation of a lee wave in the Southern Ocean with simultaneous measurements of its energetics and dynamics.

On the hydrography of Denmark Strait

Mastropole, D., R.S. Picket, H. Valdimarsson, K. Våge, K. Jochumsen, and J. Girton, "On the hydrography of Denmark Strait," J. Geophys. Res., 122, 306-321, doi:10.1002/2016JC012007, 2017.

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1 Jan 2017

Using 111 shipboard hydrographic sections across Denmark Strait occupied between 1990 and 2012, we characterize the mean conditions at the sill, quantify the water mass constituents, and describe the dominant features of the Denmark Strait Overflow Water (DSOW). The mean vertical sections of temperature, salinity, and density reveal the presence of circulation components found upstream of the sill, in particular the shelfbreak East Greenland Current (EGC) and the separated EGC. These correspond to hydrographic fronts consistent with surface-intensified southward flow. Deeper in the water column the isopycnals slope oppositely, indicative of bottom-intensified flow of DSOW. An end-member analysis indicates that the deepest part of Denmark Strait is dominated by Arctic-Origin Water with only small amounts of Atlantic-Origin Water. On the western side of the strait, the overflow water is a mixture of both constituents, with a contribution from Polar Surface Water. Weakly stratified "boluses" of dense water are present in 41% of the occupations, revealing that this is a common configuration of DSOW. The bolus water is primarily Arctic-Origin Water and constitutes the densest portion of the overflow. The boluses have become warmer and saltier over the 22 year record, which can be explained by changes in end-member properties and their relative contributions to bolus composition.

More Publications

In The News

Ice-diving drones embark on risky Antarctic mission

Scientific American, Mark Harris

To forecast sea level rise, a flotilla of undersea robots must map the unseen bottom of a melting ice shelf — if they are not sunk by it.

6 Dec 2017

Scientists get robots ready to study Antarctic ice shelves from below, with $2M boost from Paul Allen

GeekWire, Alan Boyle

Researchers from the University of Washington and Columbia University are getting ready for an unprecedented months-long campaign to study Antarctica’s ice shelves from the ocean below. Robotic Seagliders and EM-APEX profiling floats will be used to probe the ocean under ice shelves.

6 Nov 2017

Wave Glider surfs across stormy Drake Passage in Antarctica

UW News, Hannah Hickey

The University of Washington sent a robotic surf board to ride the waves collecting data from Antarctica to South America.

20 Sep 2017

More News Items

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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