Geophysical flows under location uncertainty,Part II Quasi-geostrophy and efficient ensemble spreading |
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| Authors: | V Resseguier E Mémin B Chapron |
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| Institution: | 1. Fluminance group, Inria/IRMAR/irstea, Rennes Cedex, France.;2. LOPS, Ifremer, Plouzané, France.;3. LOPS, Ifremer, Plouzané, France. |
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| Abstract: | Models under location uncertainty are derived assuming that a component of the velocity is uncorrelated in time. The material derivative is accordingly modified to include an advection correction, inhomogeneous and anisotropic diffusion terms and a multiplicative noise contribution. In this paper, simplified geophysical dynamics are derived from a Boussinesq model under location uncertainty. Invoking usual scaling approximations and a moderate influence of the subgrid terms, stochastic formulations are obtained for the stratified Quasi-Geostrophy and the Surface Quasi-Geostrophy models. Based on numerical simulations, benefits of the proposed stochastic formalism are demonstrated. A single realization of models under location uncertainty can restore small-scale structures. An ensemble of realizations further helps to assess model error prediction and outperforms perturbed deterministic models by one order of magnitude. Such a high uncertainty quantification skill is of primary interests for assimilation ensemble methods. MATLAB® code examples are available online. |
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| Keywords: | Stochastic sub-grid parameterization Uncertainty quantification ensemble forecasts |
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