Preprints
https://doi.org/10.5194/egusphere-2025-3810
https://doi.org/10.5194/egusphere-2025-3810
01 Oct 2025
 | 01 Oct 2025
Status: this preprint is open for discussion and under review for Geoscientific Model Development (GMD).

SODA4: a mesoscale ocean/sea ice reanalysis 1980–2024

Gennady A. Chepurin, James A. Carton, Luyu Sun, and Stephen G. Penny

Abstract. This paper describes the new Simple Ocean Data Assimilation version 4 (SODA4) global eddy-resolving ocean/sea ice reanalysis that spans the 45-year period 1980–2024. The reanalysis is constructed using GFDL MOM5/SIS1 numerics and ECMWF ERA5 forcings with surface and subsurface temperature and salinity observations as constraints within an optimal interpolation data assimilation algorithm. The method of construction and resulting output files are described. Comparison of the SODA4 temperature and salinity fields to observations and to the UK Met Office EN4 temperature and salinity analyses in the upper ocean shows SODA4 has marginal bias and exhibits more regional variability, with less of an imprint of the sparse and inhomogeneous distribution of observations. Comparison of transports across major ocean sections and passages are generally consistent with independent moored observations.

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Gennady A. Chepurin, James A. Carton, Luyu Sun, and Stephen G. Penny

Status: open (until 26 Nov 2025)

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Gennady A. Chepurin, James A. Carton, Luyu Sun, and Stephen G. Penny
Gennady A. Chepurin, James A. Carton, Luyu Sun, and Stephen G. Penny

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Short summary
Ocean reanalyses reconstruct the physical state of the ocean – its temperature, salinity, and currents – using historical observations to constrain a numerical simulation of the fluid equations of motion. This paper describes the SODA4 reanalysis, which is now able to resolve the oceanic eddy field and its interactions with the large-scale flow throughout most of the ocean. Reanalyses are key to climate research because they merge messy historical observations into a continuous climate record.
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