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FY05 Target - Improve climate models

Develop a coupled climate model with an interactive carbon cycle, a sub model of secondary sulfur aerosols, and an interactive terrestrial biosphere. This capability will enable studies of the interactions between the carbon cycle and climate and between secondary sulfur aerosols and climate. It will also provide a tool to quantify potentially important feedbacks between the climate system and the terrestrial biosphere.

Q1 Performance Metric: Implement a ocean biogeochemistry model that includes the effects of carbon and sulfur species in current version of the Parallel Ocean Program ocean model; implement the above within the Community Climate System Model, version 3 (CCSM3) to simulate the response of ocean biogeochemistry to climate.

December 29, 2004: We have implemented an ocean biogeochemistry model in POP version 2.0. The model is based on the ecosystem model of Doney, Moore and Lindsay (Moore et al. 2002, Deep-Sea Res., 49B, 403-462) with a trace gas module as described in a paper by Chu et al (Earth Interactions,Volume 8 (2004), Paper No. 11, available here) . The ecosystem model provides the carbon species while the trace gas module provides a variety of other important species including dimethyl sulfide (DMS), the most important ocean contribution to the sulfur cycle. Many integrations of the above model in ocean only simulations have been completed for model validation and for the improvement and calibration of biogeochemical model processes and parameters.

The version of POP 2.0 with the embedded biogeochemical model as described above has been successfully coupled within CCSM3. A five year simulation has been completed with the fully-coupled system at coarse resolution (T42 atmosphere, x3 ocean). All components, including the ocean biogeochemistry, were fully interacting with and responding to the physical fields from all other components. In addition, the ocean biogeochemistry model in this simulation provided both carbon dioxide and DMS to the coupler and we have verified that the coupler has correctly processed this data through interpolation, time averaging and merging for use in the atmosphere model. However, the carbon and sulfur coupling was only one-way (ocean to atmosphere) with no interaction with any atmospheric chemistry. No formal validation of this five-year simulation has yet occurred, but the model ran stably and the results were qualitatively reasonable when compared to existing control simulations.

The CCSM3 simulation described above and the Earth Interactions publication are evidence that we have successfully implemented an ocean biogeochemistry model that includes the effects of carbon and sulfur species in the current version of POP and that we have successfully implemented such a model within the CCSM3.

Q2 Performance Metric: 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.

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.

Q3 Performance Metric:Conduct initial testing of all model changes that include the sulfur cycle and carbon cycle in coupled climate model simulations

June 17, 2005: The SCIDAC CCSM Consortium project has worked closely with the Biogeochemsitry Working Group and the CCSM Software Engineering Group (CSEG) to assemble the components required for a coupled carbon-climate earth system model. This milestone (Q3) is meant to demonstrate that the code for a new model has been assembled. On June 12, 2005 the CSEG group tested and released the alpha version of this software for the SciDAC CCSM Consortium. The code has subsequently been executed on DOE computers at LLBL/NERSC and ORNL/NCCS. The initial test verifies that the components build and execute together using the new coupling mechanisms defined in the Q2 milestone. The code executed on the ORNL IBM p690 system "Cheetah" for ten simulated days, verifying that the modules are linked, required datasets have been provided and the carbon-climate coupling is active as well as the linkages between the oceanic and terrestrial emission of trace species to a fully active atmosphere with interactive chemistry.

The Q3 milestone is a step on the way toward examining the climate response and feedbacks that result from the inclusion of biogeochemical cycles in climate models. We have CO₂ moving from the terrestrial biosphere through the coupler into a chemically active atmosphere. The major part of the software design and engineering has been completed and we have conducted the initial tests of an alpha version of the new model. Next steps will involve refinements on the coupling, activation of more tracers, chemical interactions ,careful testing and study of the results. After problems are resolved, a 3-4 year coupled simulation will be performed. A web page will be updated with results and documentation from this effort by the end of the month.

Q4 Performance Metric:Conduct coupled simulations of the climate system including the carbon and sulfur cycles (POP2/biogeochemistry, CAM3/sulfur+carbon) with an interactive land surface model component.