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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Resseguier Valentin, Memin E., Chapron Bertrand (2017). Geophysical flows under location uncertainty, Part II Quasi-geostrophy and efficient ensemble spreading. Geophysical And Astrophysical Fluid Dynamics. 111 (3). 177-208. https://doi.org/10.1080/03091929.2017.1312101, https://archimer.ifremer.fr/doc/00385/49599/

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