Session 4

Wednesday, 18 May 2016, 11:00 AM to 12:30 PM

20 minutes per talk, 10 minutes for questions and speaker change

From	To	Name	Affiliation	Title
11:00am	11:30am	John Dabiri	Stanford University	Coherent Structure Identification from Sparse Flow Trajectories using Graph Theory
12:00pm	12:30pm	Miles Sundermeyer	University of Massachusetts Dartmouth	Observations of Dye Dispersion in the Gulf Stream Core and Across the North Wall

 

Session 4 Abstracts

Coherent Structure Identification from Sparse Flow Trajectories using Graph Theory

John Dabiri (Stanford University)
Experimental fluid mechanics is trending toward widespread use of three-component, three-dimensional
flow velocimetry, which is typically based on measurement of Lagrangian flow trajectories. This type of
data can present challenges for standard methods of coherent structure identification that rely on
measurement of the deformation gradient, as the requirement for initially closely-spaced trajectories is
often not be satisfied. Moreover, the relatively long duration over which fluid trajectories are followed
may call into question the physical relevance of linearized flow maps. In this work, we develop a technique
for coherent structure identification that does not require assumptions of initially closely-spaced
trajectories or a linearized flow map. Moreover, the method remains effective for very small numbers of
flow trajectories relative to the requirements of other Lagrangian techniques. Example applications of the
method will be presented along with opportunities to further improve its effectiveness.

Observations of Dye Dispersion in the Gulf Stream Core and Across the North Wall

Miles Sundermeyer (University of Massachusetts Dartmouth)
We report on a series of dye and drifter releases performed in the Gulf Stream core and along its north
wall in Winter 2012, two near the surface (~26-28 m) and two at depth (~55 m, and ~120 m). The primary
goal was to quantify and identify processes controlling submesoscale lateral dispersion across a strong
front, including during strong forcing conditions. Dye injections were performed in concert with Lagrangian
float deployments, each of which were tracked for between 1-5 days. Sampling focused on hydrography,
velocity, and dye distributions in a moving reference frame around the Lagrangian float, with repeat
transects through the dye patch and across the stream. Results reveal mechanisms and pathways of
transport and mixing across a strong front, including evidence of the maintenance of the front in spite of
such mixing. Processes observed include rapid subduction along isopycnals due to symmetric instability,
and the formation and detachment of streamers and/or filaments along the north wall. To the extent
possible given incomplete surveys of the dye patches, we estimate bounds on along- and cross-isopycnal
dispersion on scales comparable to the dye patch, i.e., hundreds of meters to 10s of km, accounting for
the fact that isopycnals varied from nearly vertical (outcropping) to nearly horizontal (main pycnocline).