Anisotropic Shear Dispersion Parameterization for Mesoscale Eddy Transport

Scott James Reckinger, Brown University, Department of Earth, Environmental, and Planetary Sciences, Providence, RI, United States; Montana State University, Civil Engineering Department, Bozeman, MT, United States and Baylor Fox-Kemper, Brown University, Providence, RI, United States
Abstract:
The effects of mesoscale eddies are universally treated isotropically in general circulation models. However, the processes that the parameterization approximates, such as shear dispersion, typically have strongly anisotropic characteristics. The Gent-McWilliams/Redi mesoscale eddy parameterization is extended for anisotropy and tested using 1-degree Community Earth System Model (CESM) simulations. The sensitivity of the model to anisotropy includes a reduction of temperature and salinity biases, a deepening of the southern ocean mixed-layer depth, and improved ventilation of biogeochemical tracers, particularly in oxygen minimum zones. The parameterization is further extended to include the effects of unresolved shear dispersion, which sets the strength and direction of anisotropy. The shear dispersion parameterization is similar to drifter observations in spatial distribution of diffusivity and high-resolution model diagnosis in the distribution of eddy flux orientation.
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