The NCEP climate forecast system reanalysis (CFSR) was recently completed using the NCEP coupled atmosphere-ocean-land surface-sea ice system. This paper describes the sea ice concentration data used and how sea ice concentration is assimilated in the CFSR. The record minimum of Arctic sea ice in September 2007 is clearly shown in the CFSR output. Because of the realistic sea ice distribution, there have been many improvements in the CFSR compared to the previous NCEP/NCAR Reanalysis-1 and NCEP-DOE Reanalysis-2. For instance, the surface air temperature improved in the fall over the Arctic Ocean. In addition, using the December reanalysis sea ice from 2009 and 2010, the new climate forecast system is able to accurately predict the Arctic minimum sea ice extent in September for 2010 and 2011.
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