Intercomparison of an improved 20th Century reanalysis version 2c dataset spanning 1850 to 2012
Improvements in the new version (“2c”) include an extension back to 1850 and the specification of new boundary conditions. These come from new fields of monthly COBE-SST2 sea ice concentrations and an ensemble of daily Simple Ocean Data Assimilation with Sparse Input (SODAsi.2c) sea surface temperatures. SODAsi.2c itself was forced with 20CR, allowing these boundary conditions to be more consistent with the atmospheric reanalysis. Millions of additional pressure observations contained in the new International Surface Pressure Databank version 3 are also included. These improvements result in 20CR version “2c” having comparable or better analyses, as suggested by improved 24 hour forecast skill, more realistic uncertainty in near-surface air temperature, and a reduction in spurious centennial trends in the tropical and polar regions. An intercomparison with the original NCEP-NCAR, and with NCEP CFSR, ERA-Interim, MERRA, and JRA-55 reanalyses that assimilate all available upper-air and satellite observations will also be discussed.