The LatMix Summer Campaign: Submesoscale Stirring in the Upper Ocean
Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s–1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level.
Additional Information© 2015 American Meteorological Society. AMS "Open Choice." Final form: 24 October 2014. Published online: 16 September 2015. This article is included in the LatMix: Studies of Submesoscale Stirring and Mixing Special Collection. We thank Office of Naval Research, particularly Terri Paluszkiewicz and Scott Harper, for support of the LatMix. The bulk of this work was funded under the Scalable Lateral Mixing and Coherent Turbulence Departmental Research Initiative and the Physical Oceanography Program. The dye experiments were supported jointly by the Office of Naval Research and the National Science Foundation Physical Oceanography Program (Grants OCE-0751653 and OCE-0751734). We are grateful to the captains and crews of R/Vs Cape Hatteras, Endeavor, and Oceanus, as well as the Navy Lockheed P3 Orion aircraft who made these observations possible. Many thanks to the LatMix team of ocean engineers and support staff: Mike Ohmart and Mike Kenney (Lagrangian float); John Dunlap, Jim Carlson, and Avery Snyder (EM-APEX); Chris MacKay and Kevin Bartlett (Hammerhead); Jason Gobat, Ben Jokinen, and Dave Winkel (Triaxus); Brian Guest and Leah Houghton (dye); Deborah Debiegun (drogued drifters); Cynthia Sellers and Laura Stolp (shipboard data); and many others. We thank Jules Hummon and Eric Firing for their help in calibration and processing shipboard ADCP. We also appreciate the efforts of three anonymous reviewers and their comments. In memoriam of Murray Levine.
Published - bams-d-14-00015.1.pdf
Supplemental Material - 10.1175_bams-d-14-00015.2.pdf
Supplemental Material - latmix2011.kmz