Distributed Ocean–Atmosphere Modeling and Sensitivity to the Coupling Flux Precision: The CATHODe Project

Abstract

The authors present the distribution of a coupled ocean?atmosphere global circulation model. The atmospheric (ARPEGE) and the oceanic (OPA) components run separately at different sites; the coupling is achieved through the exchanges of fluxes via the coupler (OASIS) and the three independent programs communicate together through the 2-Mbit RENATER network. The coupling and distributing procedure is based on the PVM software and is validated by 1-yr simulations. Performances and difficulties raised by the distributed environment are also presented. An additional study deals with the sensitivity to the precision in exchanged data in coupled mode. This question is addressed by introducing small artificial perturbations into the forcings of each component. The transient growth of these perturbations is first followed over 10 days on specific grid points. A global spatio-temporal analysis is then performed over the planet for 1-yr simulations. During the first 10 days of the experiments, the ?error? dynamics is amplified by the atmosphere with a doubling time of the order of 5 days, while the upper ocean simply relaxes toward equilibrium. For long time ranges of simulation, errors tend to saturate and oscillate around a plateau, following the seasonal cycle. Spatio-temporal studies prove that the most sensitive areas to the precision in exchanged forcings are related to the regions where the variability is the most pronounced. These analyses are integrated into the general studies of predictability in coupled ocean?atmosphere models.