Stochastic Parametrization of Ocean Mesoscale Eddies

Friday, March 15, 2013 - 10:30am - 11:00am
Keller 3-180
Laure Zanna (University of Oxford)
The ocean contains a vigorous mesoscale eddy field with spatial scales of approximately 10 to 100km, evolving over time scales from weeks to months. These eddies are important in establishing the ocean's circulation and tracer properties. Grid spacing of roughly 10 km and smaller are necessary to properly simulate the eddy field, therefore ocean climate models are unlikely to routinely resolve geostrophic eddies and their effect needs to be parametrized. The goal of our study is to construct a stochastic parameterization of mesoscale eddies in ocean modelsusing the statistics derived from the output of high resolution model. A quasi-geostrophic (QG) model in a double-gyre configuration is run at resolution of 7.5 km (eddy-resolving). The output of the high-resolution model is coarse-grained and used to calculate probability distribution functions for the eddy source term conditioned on the model state. A stochastic parametrization is then created using the evaluated conditional probability distribution functions and implemented in a coarse resolution version of the QG model. The dynamics of the mean flow, its variability and eddy-mean flow interaction are examined and compared with deterministic closures of geostrophic eddies.
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