INGV Coupled Model Documentation

The ocean model is similar to the one used by Météo-France, i.e., OPA 8.1. OPA is the ocean modeling system developed by the LODYC team in Paris (Madec et al. 1998). OPA is a finite differences OGCM and solves the primitive equations with a non-linear equation of state on an Arakawa C-grid. The present configuration uses a rigid lid. The horizontal mesh is orthogonal and curvilinear on the sphere. To overcome the singularity at the North Pole, the northern point of convergence has been replaced by two poles located on Asia and North America. Its space resolution is roughly equivalent to a geographical mesh of 2 by 1.5 degrees (with a meridional resolution of 0.5 degrees near the Equator). There are 31 vertical levels, with 10 levels in the top 100 metres. There is no interactive sea-ice model in the configuration used for the seasonal forecasts: sea-ice cover is relaxed towards an observed monthly climatology.

The ocean initial conditions have been produced by forcing OPA with the ERA-40 fluxes for the 1987-1996 period. A 6-year spin up of the model has been done with the ERA-15 fluxes for the period 1981-1986. The 9 members are obtained by adding wind stress perturbations in the forced ocean run.

The initial conditions of the ocean-atmosphere system for each starting date have been obtained from separate integrations of the ocean and atmosphere model components in forced mode. In order to represent the uncertainties in the initial state of the ocean, an ensemble of 9 ocean initial conditions has been produced. Specifically, the ocean model, ORCA, has been first integrated for a 30-year (1972-2001) control run, where the ocean has been forced with momentum, heat and mass flux data from the ECMWF 40-year re-analysis (ERA-40). Then, two perturbed ocean simulations, for the same period, have been performed adding daily wind stress perturbations to the ERA-40 momentum fluxes. The wind stress perturbations have been randomly taken from a set of monthly differences between two quasi-independent analyses. Furthermore, in order to represent the uncertainty in SSTs, four SST perturbations have been added at the initial conditions of the hindcasts. As for the wind perturbations, the SST perturbations are constructed to represent differences between two quasi-independent SST observational data sets. Atmospheric initial conditions have been obtained from an AMIP-type run performed with the atmosphere component of the model forced with observed SSTs (HadISST) for the period 1972-2001.

A complete description of the climatology simulated by the coupled model in long control simulations, and an analysis of the capability of the model to reproduce the main modes of the climate variability can be found in Gualdi et al. (2003a, 2003b), Guilyardi et al. (2003) and Corti et al. (2003).

Corti S., S. Gualdi and A. Navarra, 2003. Analysis of the midlatitude weather regimes in the 200-year control integration of the SINTEX model. Annals Geophys, 46, 27-37.

Gualdi S., E. Guilyardi, A. Navarra, S. Masina and P. Delecluse, 2003. The Interannual Variability in the Tropical Indian Ocean as Simulated by a CGCM. Clim. Dyn., 20, 567-582.

Gualdi S., A. Navarra, E. Guilyardi, and P. Delecluse, 2003. Assessment of the Tropical Indo-Pacific Climate in the SINTEX CGCM. Annals Geophys, 46, 1-26.

Guilyardi E., P. Delecluse, S. Gualdi and A. Navarra, 2003. Mechanisms for ENSO phase change in a coupled GCM. J. Climate, 16, 1141-1158.

Madec G., P. Delecluse, M. Imbard and C. Levy, 1998. OPA version 8.1 ocean general circulation
model reference manual. Technical Report, LODYC/IPSL, Note 11, Paris, France, pp. 91.

Roeckner E., 1996. The atmospheric general circulation model ECHAM-4: model description and simulation of present-day climate. Max-Planck-Institut für Meteorologie, Rep. No 218, Hamburg, Germany, 90 pp.