Submesoscale Routes to Lateral Mixing in the Ocean
Abstract
The long-term goal of this project is to determine whether lateral mixing at O(1-10 km) scales is due to a balanced or unbalanced downscale cascade from the mesoscale, or to local vertical mixing by internal waves and surface forcing. Our work will test hypothesis 3 of the white paper "Scalable Lateral Mixing and Coherent Turbulence." Non-QG, submesoscale instabilities feed a forward cascade of energy, scalar, and Ertel PV variance, which enhances both isopycnal and diapycnal mixing. Related hypotheses are that submesoscale variability is associated with coherent structures and anisotropic mixing. We ran a number of process studies using a non-hydrostatic model. We examined processes in a domain approximately 100 km x 200 km, but we have improved the model to run on much larger domains (500 km x 1000 km) at the same horizontal resolution. The 3D non-hydrostatic submesoscale resolving model has been optimized and scaled up for use on modern multi-core computer architecture, achieving an efficiency that allows modeling larger domains with meso- and submesoscale interactions. Numerical simulations have been carried out for a baroclinically unstable front in a periodic channel, forced by a constant surface wind stress in many cases. We have analyzed the skew and residual components of across-front buoyancy fluxes and the along-isopycnal bolus transport driven by sub-mesoscale eddies. Pre-observational process studies have been carried out with characteristic values of stratification, mixed layer depth, and lateral buoyancy gradients. We have analyzed numerical experiments in which dye dispersion is examined for the submesoscale frontal instabilities in the presence of wind. The dye is released at two depths in zonal streaks at the beginning of the simulation. The variance in dye concentration is analyzed in time along isopycnal surfaces to study lateral mixing of the dye at various isopycnal depths as a function of mixed layer depth and lateral buoyancy gradient.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2009
- Accession Number
- ADA527292
Entities
People
- Amala Mahadevan
- Amit Tandon
Organizations
- University of Massachusetts Dartmouth