An Ensemble Reanalysis with the Community Earth System Model 2.0

The National Center for Atmospheric Research (NCAR) has recently released version 2.0 of the Community Earth System Model (CESM 2.0). A twenty-year, 80-member ensemble atmospheric reanalysis with 1-degree resolution in the CAM6 atmospheric model is being produced using NCAR’s Data Assimilation Research Testbed (DART) to support a variety of climate research goals. A standard configuration of CAM and the CLM5 land surface model will be coupled to a prescribed ocean and sea ice. Two streams will be used to generate a final product that extends from 1999 to the present. Observations assimilated will include in situ observations used in the operational NCEP CFSR reanalysis along with GPS occultation observations and remote sensing temperature retrievals. The primary goal is to provide an ensemble of atmospheric forcing that can be used to generate additional ensemble reanalyses for other components of CESM including CLM, the POP and MOM6 ocean models, and the CICE sea ice model. A high-quality ensemble mean analysis is important, but realistic ensemble variability that is consistent with the observing system is crucial to performing ensemble data assimilation for the other components. The reanalysis will also be used to assess the performance of CAM and to provide initial conditions for forecasts using CAM, the high-top WACCM variant of CAM, and a version of CAM with chemistry. Evaluation of initial results will assess short-term forecasts in observation space for root mean square error, ensemble spread, and ensemble consistency.