Stochastic parameterization of subgrid-scale processes in coupled ocean-atmosphere systems: Benefits and limitations of response theory

摘要

A stochastic subgrid-scale parameterization based on the Ruelle's responsetheory and proposed in Wouters and Lucarini [2012] is tested in the context ofa low-order coupled ocean-atmosphere model for which a part of the atmosphericmodes are considered as unresolved. A natural separation of the phase-spaceinto an invariant set and its complement allows for an analytical derivation ofthe different terms involved in the parameterization, namely the average, thefluctuation and the long memory terms. In this case, the fluctuation term is anadditive stochastic noise. Its application to the low-order system reveals thata considerable correction of the low-frequency variability along the invariantsubset can be obtained, provided that the coupling is sufficiently weak. Thisnew approach of scale separation opens new avenues of subgrid-scaleparameterizations in multiscale systems used for climate forecasts.