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Geophysical flows under location uncertainty, Part II Quasi-geostrophy and efficient ensemble spreading
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.
Keyword(s)
Stochastic sub-grid parameterization, Uncertainty quantification, ensemble forecasts
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File | Pages | Size | Access | |
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Publisher's official version IN PRESS | 36 | 1 Mo | ||
Author's final draft | 34 | 1 Mo |