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A reanalysis of
ocean climate

Background The goal of SODA is to reconstruct the historical physical (and eventually biogeochemical) history of the ocean. 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, we want to be helpful. Our goal is to provide a reliable 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) represents a major upgrade of SODA. The model has been switched to GFDL MOM5/SIS numerics with eddy permitting 1/4°x1/4°x50lev resolution (28km at the Equator down to <10km at polar latitudes) . This model is 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 SODA3 retains a low cost specified error covariance.

For these experiments we follow the usual procedure in the ocean community and input specified hourly to daily downwelling solar and longwave radiation and precipitation, as well as 2m air temperature and specific humidity as well as 10m winds, along with SST and ocean currents into a set of bulk formulas to compute surface heat, freshwater, and momentum fluxes. Because of the sensitivity of the results on the choice of bulk formulas here we explore two different bulk formulas: Large and Yeager and COARE4.

Bias Detection An emphasis for SODA3 has been to quantify and hopefully reduce bias (systematic error). Bias enters ocean reanalysis in four ways: biased initial conditions, biased forcing, model biases, and biased observations (both measurements and sampling patterns). We think the worst of these are surface forcing and the biases in the ocean observations prior to the deplyment of the Argo system in the early 2000s. To begin to address this issue we are carrying out an ensemble of ocean reanalyses using the same reanalysis system, but with forcing provided by different atmospheric reanalyses shown in the table below (names in grey have not been completed or checked yet).

Flux Bias Correction Since the fluxes leaving the atmosphere must match the fluxes entering the ocean we can use information about the observation - model misfit to correct the atmospheric fluxes. A manuscript is in review describing the impact of flux bias correction (Carton, Chepurin, Chen, and Grodsky, 2017). This procedure has been applied to correct the fluxes marked with an (*). The reanalysis fields for these experiments are available through the pulldown tabs above or through the live links in the Table.

SODA3.3.0NO MERRA2* Large-Yeager 1980-2015
SODA3.3.1YES MERRA2* Large-Yeager 1980-2015
SODA3.3.2 YES MERRA2*COARE41980-2015
SODA3.4.0NO ERA-I*Large-Yeager 1980-2015
SODA3.4.1YES ERA-I*Large-Yeager 1980-2015
SODA3.4.2YES ERA-I*COARE41980-2015
SODA3.5.1YES ERA20C*COARE41980-2010
SODA3.6.1YES CORE2Large-Yeager 1980-2009
SODA3.7.0NO JRA-55*COARE41980-2013
SODA3.7.2YES JRA-55*COARE41980-2013
SODA3.8.1YES 20CRv2*Large-Yeager 1980-2013
SODA3.9.1YES OAfluxLarge-Yeager 1980-2015
SODA3.10.1YES CFSRRLarge-Yeager 1980-2015
SODA3.11.0NO DFS5.2COARE41980-2015
SODA3.11.2YES DFS5.2COARE41980-2015
(* indicates there has been flux-correction. Members marked in grey are not yet available)

SODA3 Future Hopefully in the next year (2018) we will begin to encorporate quasi-isopycnal dynamics, an improved error covariance, enhanced resolution, and introduce ocean biogeochemistry.

SODA4 The next major revision after that will be, or be part of, a fully coupled atmos/ocean/ice reanalysis.

For additional information send us email: Gena Chepurin and Jim Carton. If you don't get a response we've gotten distracted. Please keep trying!

Join the SODA3 email list

Acknowledgements SODA relies on extensive collaborations. In addition to the National Science Foundation Physical Oceanography Program we owe debts to: NOAA/GFDL, NOAA/NCEP, NOAA/NESDIS (especially the Laboratory for Satellite Altimetry and NCEI), NASA/GMAO, and the NASA MAP and Physical Oceanography programs. Many individuals have contributed to SODA including: Tim Boyer, Gil Compo, Dick Dee, Eric Hackert, Sirpa Hakkinen, Sasha Ignatov, Eugenia Kalnay, Syd Levitus, Matt Maltrud, Julie McClean, Laury Miller, Steve Penny, R. Raghunath, James Reagan, Tony Santorelli, Mike Steele, and most notably Ben Giese, Xianhe Cao, and Hank Seidel.

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