Modelling the ocean circulation with random numbers

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The ocean contains a vigorous geostrophic mesoscale eddy field with spatial scales of approximately 100km at mid-latitudes, evolving over time scales from weeks to months. These eddies are important in establishing the ocean's circulation and tracer distributions in the ocean' interior. In the vicinity of the Gulf Stream and the Kuroshio's extensions and in the Antarctic Circumpolar Current (ACC), eddies are the primary means by which heat is transported poleward. However, to adequately simulate the mesoscale eddy field and associated turbulent cascades of tracers in numerical models, horizontal resolution of at least 10 km is necessary. It is therefore unlikely that climate models will systematically resolve ocean eddies and their effect needs to be parametrized. Large improvements have been made in the implementation of deterministic parameterizations of mesoscale eddies. Despite such improvements, the major source of model error remains the imperfect or missing closure of these subgrid scale processes.In the current proposal, we aim to improve our knowledge of how ocean eddy variability influences the large-scale climate. We also aim to develop a novel stochastic closure as an alternative approach to the current deterministic parameterization. Such stochastic closure offers the advantage of an explicit representation of the inherent uncertainty associated the parametrized processes. The new stochastic parameterization of eddies will be tested on a state-of-the-art climate model and the impact on the mean climate, its variability and predictability will be investigated.