Stochastic schemes for the perturbation of the atmospheric boundary conditions in ocean general circulation models

Advancing the representation of uncertainties in ocean general circulation numerical models is required for several applications, ranging from data assimilation to climate monitoring and extended-range prediction systems. The atmospheric forcing represents one main uncertainty sources models. Here, we formulate revise different approaches perturb air-sea fluxes used within boundary conditions. In particular, perturbation performed either through i) stochastic modulation transfer coefficients; ii) flux tendencies; iii) coarse-graining sub-grid computation fluxes; or iv) multiple bulk formulas. schemes are implemented tested NEMO4 model, at an eddy-permitting resolution on a domain covering North Atlantic Arctic oceans Mediterranean Sea. A series 22-year 4-member ensemble experiments with analyzed period 2000-2021, results compared terms mean and, when applicable, spread principal oceanic diagnostics. Results indicate that schemes, general, can significantly improve some verification skill scores (e.g. against drifter current speed, SST analyses, hydrographic profiles) cases, enhance mesoscale activity weaken large-scale circulation. response, however, depending specific scheme, whose choice thus depends target application, as detailed paper. These findings foster adoption these both operational forecasts coupled long-range systems, where conditions perturbations may contribute performance increases.