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A reanalysis of
ocean climate

Goal 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, we want to be helpful to 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 1/4°x1/4°x50lev resolution (28km at the Equator down to <10km 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. A description of SODA3 and its comparison to SODA2 is available: Carton, Chepurin, and Chen (2018).

Bias correction: One of the focusses for SODA3 has been to identify, quantify, and hopefully 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 as discussed in Carton et al. (2018). Additional members explore sensitivity to data selection.

10 November, 2018 We have completed an additional ensemble member (soda3.12.2). Two manuscripts are under submission which we invite you to look at: 1) comparing the SODA3 ensemble to alternative ocean reanalyses (link) and 2) examining the historical record of ocean heat storage as it appears in SODA3 (link). Any comments will, of course, be appreciated. We will be beginning a collaboration with UNSW scientists to explore the impact of upgrading to eddy-resolving horizontal (0.1°x0.1°) resolution and shallow mixed layer-resolving (2m) vertical resolution. We believe that as the ocean/sea ice models which underlie the reanlysis improve the analysis will be less relient on the details of the assimilation and thus more accurate.

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

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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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