Stochastic parametrization of ocean mesoscale eddies

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 this study is to construct a stochastic parameterization of mesoscale eddies in ocean models in order to replace or improve current deterministic closure schemes. 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 forcing conditioned on the model state. A stochastic parametrization is then created using the evaluated conditional probability distribution functions and implemented as Markovian and/or non-Markovian processes in a coarse resolution run of the QG model. The dynamics of the mean flow, its variability and eddy-mean flow interaction are examined for each case of the stochastic parametrization and compared with deterministic closures of geostrophic eddies. Reference: Porta Mana PGL and L. Zanna: Stochastic parametrization of ocean mesoscale eddies, In Prep. for J. of Climate, 2012