Development of a probabilistic ocean modelling system based on NEMO 3.5: application at eddying resolution

This sources presents the technical implementation of a new, probabilistic version based on NEMO 3.5 ocean/sea-ice modelling system (Bessières et al., 2017). Ensemble simulations with N members running simultaneously within a single executable, and interacting mutually if needed, are made possible through an enhanced MPI strategy including a double parallelization in the spatial and ensemble dimensions. An example application is then given to illustrate the implementation, performances and potential use of this novel probabilistic modelling tool. A large ensemble of 50 global ocean/sea-ice hindcasts has been performed over the period 1960-2015 at eddy-permitting resolution (1/4 o ) for the OCCIPUT project. This application is aimed to simultaneously simulate the intrinsic/chaotic and the atmospherically-forced contributions to the ocean variability, from meso-scale turbulence to interannual-to-multidecadal time scales. Such an ensemble indeed provides a unique way to disentangle and study both contributions, as the forced variability may be estimated through the ensemble mean, and the intrinsic chaotic variability may be estimated through the ensemble spread.

Reference: Bessières, L., Leroux, S., Brankart, J.-M., Molines, J.-M., Moine, M.-P., Bouttier, P.-A., Penduff, T., Terray, L., Barnier, B., and Sérazin, G.: Development of a probabilistic ocean modelling system based on NEMO 3.5: application at eddying resolution, Geosci. Model Dev., 10, 1091-1106, doi:10.5194/gmd-10-1091-2017, 2017.