CLIMBER-3a

Earth System Models of Intermediate Complexity (EMICs) attempt to overcome the gap between simple and comprehensive models (see review by Claussen et al. (2002)). Such models describe a considerable number of processes and feedbacks in the climate system, generally including more components than most coupled atmosphere-ocean general circulation models (AOGCMs). Thanks to their low spatial resolution and simplified governing equations, they are computationally less expensive. The CLIMBER-3 project seeks to develop an EMIC of a new generation, beyond the highly successfull CLIMBER-2. The CLIMBER-3a EMIC represents the first version of this next generation. It has evolved from CLIMBER-2. The main difference with respect to CLIMBER-2 is its oceanic component, which has been replaced by a state-of-the art ocean model including an ocean general circulation model (OGCM), a biogeochemistry module and a state-of-the-art sea-ice model. The atmospheric resolution was slightly increased. Thus, CLIMBER -3a includes modules describing the atmosphere, land-surface scheme, terrestrial vegetation, ocean, sea-ice, and ocean biogeochemistry. Due to its relatively simple atmospheric component it is approximately two orders of magnitude faster than coupled AOGCMs, allowing the integration of a much larger number of integrations and sensitivity studies, as well as longer simulations. At the same time its oceanic component confers to it a larger degree of realism compared to those EMICs which include zonally averaged oceanic components. The model is thus suited for large-scale climate dynamics with a special focus on the ocean dynamics. The coupling does not include flux corrections for heat and freshwater fluxes. Exchange of momentum fluxes between the ocean and the atmospehre is semi-interactive. The comparison against the climatologies shows that CLIMBER-3a describes satisfactorily the large-scale characteristics of the atmosphere, ocean and sea-ice on seasonal timescales ( Montoya et al., (2005)) The CLIMBER-3a model is applied in the PIK-projects AO-Quest, C-Quest, ICE-Quest and INTEGRATION.