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Carton, James A., Gennady A. Chepurin, and Ligang Chen, 2018: SODA3:
A New Ocean Climate Reanalysis. J. Climate, 31, 6967-6983 (DOI:
10.1175/JCLI-D-18-0149.1), URL:
https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-18-0149.1.
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The goal of SODA is to reconstruct the historical physical (and
eventually biogeochemical) history of the ocean since the beginning
of the 20th century. As its name implies, the Simple Ocean Data
Assimilation ocean/sea ice reanalysis (SODA) uses a simple
architecture based on community standard codes with resolution
chosen to match available data and the scales of motion that are
resolvable. Agreement with direct measurements (to within
observational error estimates) as well as unbiased statistics are
expected. While SODA remains a university-based research project, an
objective is to support potential users by providing a reliable,
well-documented, source of seasonal climate time-scale ocean
reanalysis to complement the atmospheric reanalyses available
elsewhere (NOAA/EMC, NASA/GMAO, and ECMWF, for example).
SODA3 (SODA Version 3) is the latest release of SODA. The model has
been switched to GFDL MOM5/SIS1 with eddy permitting 0.25 degree by
0.25 degree by 50 level resolution (28 kilometers at the Equator
down to less than 10 kilometers at polar latitudes), similar to the
ocean component of the GFDL CM2.5 coupled climate model, and
includes the same SIS1 active sea ice model. A number of
improvements have been included in the sequential DA filter, but for
many reanalyses SODA3 retains a pre-specified flow-dependent error
covariance.
One of the focuses for SODA3 has been to identify, quantify, and
limit sources of bias. A major source of bias is in the forward
model that predicts the evolution of the flow. A major (but not the
only) source of model bias, in turn, is introduced through bias in
the meteorological fluxes (heat, freshwater, and momentum). To
address this problem SODA3 is an 'ensemble' reanalysis, the spread
of whose members provides information about sensitivity to errors in
surface forcing. Many of these ensemble members are driven by fluxes
that have been bias-corrected.
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