LatMix: Studies of Submesoscale Stirring and Mixing
Description:
Stirring and lateral mixing by submesoscale processes are believed to play an important role in setting the distribution of energy, vorticity, momentum, and tracers in the ocean, and their transfer from one scale to another. But an inadequate understanding of the underlying processes has limited our ability to reliably include their effects in general circulation models. The ONR Departmental Research Initiative, Scalable Lateral Mixing and Coherent Turbulence (LatMix), aimed to address this gap through intensive observations and modeling of these processes. The initiative included two field efforts in the vicinity of the Gulf Stream. In the first field campaign (June, 2011) three ships and an airborne LIDAR system examined processes in the seasonal pycnocline of the mesoscale eddy field just to the southeast of the Gulf Stream during relatively quiescent early summer conditions. The second campaign (February-March, 2012) was conducted from two ships in the core of the Gulf Stream in very dynamic late-winter conditions. Detailed field observations, along with high-resolution numerical modeling and remote sensing data, revealed a host of intricate mesoscale and submesoscale structures. Data analysis, theoretical work, and numerical simulations continue to elucidate a range of processes at scales of 0.1 to 10 km that lead to lateral mixing and energy transfer. This AMS special collection brings together papers presenting many of the results from this project. The overview article for this collection can be found here.
Collection organizers:
James R. Ledwell, Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution
Gualtiero Badin, Institute of Oceanography, University of Hamburg
Amala Mahadevan, Department of Physical Oceanography, Woods Hole Oceanographic Institution
Andrey Shcherbina, Applied Physics Laboratory, University of Washington, Seattle
Miles A. Sundermeyer, School for Marine Science and Technology, University of Massachusetts, Dartmouth
LatMix: Studies of Submesoscale Stirring and Mixing
Abstract
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.
Abstract
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.
