Joint Seminar: The development of the new GEOS-MITgcm atmosphere-ocean model for coupled data assimilation system

During the last two plus decades, The Goddard Earth Observing System (GEOS) and Massachusetts Institute of Technology (MIT) modeling groups have developed, respectively, atmosphere-only and ocean-only global general circulation models. These two models (GEOS and MITgcm) have demonstrated their data assimilation capabilities with the recent releases of the Modern Era Reanalysis for Research Applications, Version 2 (MERRA-2) atmospheric reanalysis and the Estimating the Circulation and Climate of the Ocean, Version 4 (ECCO-v4) ocean (and sea ice) state estimate. Independently, the two modeling groups have also produced global atmosphere-only and ocean-only simulations with km-scale grid spacing which proved invaluable for process studies and for the development of satellite and in-situ sampling strategies.

Recently, a new effort has been made to couple these two models and to leverage their data-assimilation and high resolution capabilities (i.e., eddy-permitting ocean, cloud-permitting atmosphere). The focus in the model development is put on sub-seasonal to decadal time scales. In this talk, I discuss the new coupled model and present some first coupled simulation results as well as several ocean-only simulations aimed to imitate different flavors of the future coupled data assimilation system.

In the first part of the talk I will show results from an ocean-only set of experiments in which different forcing methods were used to force MITgcm ocean model in its ECCO-v4 configuration (1992-2011) with MERRA-2 atmospheric reanalysis fields instead of the ECCO-v4 adjoint optimized ERA-Interim state variables. The results from this set of experiments have implications for ocean-model forcing recipes and clearly reveal the undesirable consequences of limiting the feedbacks in data assimilation systems.In the second part I will present some results from a coupled GEOS-MIT simulation, whereby we have coupled a cubed-sphere-720 (~ 1/8°) configuration of the GEOS atmosphere to a lat-lon-cap-1080 (~ 1/12°) configuration of the MIT ocean. We compare near-surface diagnostics of this fully coupled ocean-atmosphere set-up to equivalent atmosphere-only and ocean-only simulations. In the comparisons we focus in particular on the differences in air-sea interactions between sea surface temperature (SST) and wind for the coupled and uncoupled simulations.




13:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Ehud Strobach, NASA GSFC in Maryland, USA


Bjorn Stevens

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