Session 1

Tuesday, 17 May 2016, 9:00 AM to 10:30 AM

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

From	To	Name	Affiliation	Title
9:00am	9:30am	Amy Bower	Woods Hole Oceanographic Institution	A Review of High-Resolution Subsurface Lagrangian Observations in the Ocean
9:30am	10:00am	Ivan Savelyev	US Naval Research Lab	Characterizing upper ocean hydrodynamics using infrared and hyperspectral airborne remote sensing
10:00am	10:30am	James Ledwell	Woods Hole Oceanographic Institution	Stirring of Tracers within the Stratified Ocean

 

Session 1 Abstracts

A Review of High-Resolution Subsurface Lagrangian Observations in the Ocean

Amy Bower (Woods Hole Oceanographic Institution)
For more than four decades, physical oceanographers have been tracking fluid particle motion using
acoustically tracked, neutrally buoyant floats. The existence of a mid-depth minimum in sound speed—
the sound or SOFAR (Sound Fixing And Ranging) channel—allows for tracking over large spatial scales
(>1000 km) with high temporal/spatial resolution (< 1 day/< 5 km). The original SOFAR float, developed in
the early 1970s, was replaced by the lighter, smaller, more manageable, cost-effective RAFOS float system
in the late 1980s, with several variations emerging in the following decades. Hundreds of trajectories have
been collected from high latitudes to the tropics, at depths from near-surface to the abyss, in the Atlantic,
Pacific, Indian and Southern Oceans. Depending on the research topic, trajectories vary in length from
months to years, and can track 2D or 3D fluid motion.
This talk will review some of the unique discoveries made using these Lagrangian observing tools,
summarize the technology and plans for future development, and describe new results from a study of
the deep circulation in the Gulf of Mexico. The high-resolution (compared to typical Lagrangian integral
time scales) trajectories have been particularly enlightening in studies of (a) the formation, propagation,
kinematics and dynamics of mesoscale and submesoscale subsurface eddies; (b) dispersion and Lagrangian
statistics; (c) quasi-Eulerian statistics over large spatial regions; and (d) the structure of narrow boundary
currents and water mass spreading pathways. Information on all four of these areas is being gleaned from
a set of 180 RAFOS floats deployed in the Gulf of Mexico in the depth range 1500-2500 m during 2011-
2015.

Characterizing upper ocean hydrodynamics using infrared and hyperspectral airborne remote sensing

Ivan Savelyev (US Naval Research Lab)
This presentation will describe a series of airborne remote sensing experiments conducted by the Naval
Research Lab (NRL) over the coastal ocean. While NRL conducts airborne tests using widest variety of
active and passive sensors across the EM spectrum, for the coastal applications the most practical sensors
are often found to be mid-wave infrared and hyperspectral visible-near IR passive sensors, which will be
covered in more detail here. Recent improvements in infrared and hyperspectral imaging technologies, as
well as in high grade positioning systems, enabled airborne remote sensing to become a relatively
inexpensive and highly effective component in coastal ocean studies. Capturing scales from meters to
1000s of meters, airborne remote sensing has been shown to resolve spatial, as well as temporal structures
of such processes as submesoscale eddies, fronts and frontal instabilities, wakes behind islands and
submerged mounts, breaking surface and internal waves, rip currents, convection and Langmuir cells,
among others. Spatially rich data provided by an airborne sensor is often unique and unattainable by any
other conventional oceanographic instrument. On the other hand, it is often hard to quantify airborne
imagery in terms of commonly used oceanographic parameters, making concurrent in-water ground truth
measurements an essential counterpart of an airborne survey.

Stirring of Tracers within the Stratified Ocean

James Ledwell (Woods Hole Oceanographic Institution)
Glimpses of the dispersion of tracer in the stratified ocean interior have been obtained from a number of
tracer release experiments. As in most other fluid stirring situations, streaks of tracer develop, indicating
the action of high strain and in the direction orthogonal to streaks barriers to transport are apparent. The
processes seem to prevail at the full range of scales investigated, from the 100-m scale of the initial
releases, to the 100-km scale of mesoscale eddies. Rates of straining at these various scales can be crudely
estimated from the evolution of the tracer fields, as can rates of dispersion across the barriers. Results
from experiments in the main pycnocline of the North Atlantic, the salt finger staircase in the main
pycnocline east of Barbados, the deep Brazil Basin, the mid-depth Gulf of Mexico, and the Circumpolar
Deep Water of the Antarctic Circumpolar Current will be presented. In the case of the Antarctic
Circumpolar Current, inhibition of transport of tracer across the Polar Front will be discussed.