March 31, 2005: The SciDAC Climate Consortium has completed the second quarter deliverable towards the creation of a coupled climate model with interactive carbon and sulfur biogeochemistry. For the second quarter of FY05 the task was: "Implement a CCSM3 coupler to simulate the exchange of carbon between the atmosphere, ocean and terrestrial biosphere, and the exchange of sulfur species between atmosphere and ocean." Working with scientists at NCAR, we have established a branch in the CCSM repository for biogeochemistry development. One of the first accomplishments was to alter the coupler-model interface in CCSM3 to simplify the addition and removal of coupled fields. Instead of using hardcoded integer indices for each field, a new query function allows each model to determine the index for accessing a field from the coupler buffers. This in turn can be used by the models to determine at runtime what fields are active. With this new scheme, we have implemented the following exchanges: CO2 concentration is passed from the atmosphere to the coupler and then to the land and the ocean. CO2 flux is passed from the ocean and land to the coupler, then to the atmosphere where they are combined into a total flux. The flux of dimethyl-sulfide (DMS) between the ocean and atmosphere is passed from the ocean to the coupler and then to the atmosphere. A design document describing these changes has been prepared and is available at this link (click here). We are also keeping the CCSM Biogeochemistry Working Group informed of our progress.
All changes have been run successfully within a 5 day run of a fully coupled configuration ("B" run) of CCSM3 on seaborg at NERSC. The coupler correctly performs all mappings between the atmosphere and ocean grids for the DMS flux, ocean-atmosphere CO2 flux and atmosphere CO2 concentration. This was verified by inspection of the exchanged fields in the coupler history files. Constant values were used for the CO2 and DMS fluxes while the CO2 concentration was predicted by the atmosphere model from an initial constant field.