ECHAM-MOM Dynamical model
International Research Institution for Climate Prediction (IRI)
Palisades, New York, U.S.
The ECHAM-MOM is a comprehensive coupled atmosphere-ocean general circulation model (CGCM) that does not employ flux correction.
The system combines the Max Planck Institute for Meteorology ECHAM4.5 AGCM (Roeckner et al. 1996) and the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model, version 3 (Pacanowski and Griffies 1998) using the Ocean Atmosphere Sea Ice Soil (OASIS) coupling software (Terray et al. 1999) produced by the European Center for Research and Advanced Training in Scientific Computation (CERFACS). The atmospheric component is a spectral model with T42 horizontal resolution and 19 unevenly spaced hybrid sigma-pressure layers. Greater detail is available in Roeckner et al. (1996). The MOM3 ocean model is a finite difference treatment of the primitive equations of motion using the Boussinesq and hydrostatic approximations in spherical coordinates. The ocean domain spans 74°S to 65°N, and the computational grid has 1.5° horizontal resolution (1/2° meridional resolution near the equator) and 25 vertical levels. Information is exchanged between the AGCM and the OGCM once per simulated day using the OASIS software. The models are directly coupled with no empirical corrections applied to fluxes or SST. Systematic error in the system is relatively small, consisting of a cold SST bias. The ECHAM-MOM has weak, approximately biennial, self-sustained ENSO oscillations of the type commonly observed in coupled GCMs. Initial conditions for the ocean model are taken from an ocean data assimilation (ODA) system produced at GFDL using a 3D variational scheme (Derber and Rosati 1989; Schneider et al. 2003). The ODA uses a higher-resolution version of MOM3 (1° horizontal resolution with 1/3° meridional resolution near the equator, 40 vertical levels) but with identical physics and parameter settings. The ODA product is interpolated to the ECHAM-MOM grid. The atmospheric initial conditions are taken from AGCM simulations forced by the ODA SST to bring low-level model winds into approximate equilibrium with the SST of the OGCM initial condition. Following some subsequent refinement, this system was implemented into ENSO forecast operations at the IRI.
Browse forecasts of this model, combined with those of the COLA Anomaly model in recent quarterly issues of the Experimental Long-Lead Forecast Bulletin, issued by COLA.
Contact: Dave DeWitt: daved@iri.columbia.edu
References:
Derber, J., and A. Rosati, 1989: A global oceanic data assimilation system. J. Phys. Oceanog., 19, 1333-1347.
DeWitt, D. G., 2005: Retrospective forecasts of interannual sea surface temperature anomalies from 1982 to present using a directly coupled atmosphere-ocean general circulation model. Mon. Wea. Rev., 133, 2972-2995.
Pacanowski, R. C., and S. M. Griffes, 1998: MOM 3.0 manual. NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ, 608 pp.
Schneider, E. K., D. G. DeWitt, A. Rosati, B. P. Kirtman, L. Ji, and J. J. Tribbia, 2003: Retrospective ENSO forecasts: Sensitivity to atmospheric model and ocean resolution. Mon. Wea. Rev., 131, 3038-3060.
Roeckner, E., and Coauthors, 1996: The atmospheric general circulation model ECHAM4: Model description and simulation of present day climate. Rep. 218, Max-Planck-Institut fur Meteorologie, 90 pp. [Available from MPI fur Meteorologie, Bundesstr. 55, 20146 Hamburg, Germany.].
Terray, L., A. Piacentini, and S. Valcke, 1999: OASIS 2.3, Ocean Atmosphere Sea Ice Soil: User $(B!G (Bs guide. CERFACS Tech. Rep. TR/CMGC/99/37, Toulouse, France, 82 pp. [Available online at www.cerfacs.fr/globc/publication.html.].