SODA3¶

Simple Ocean Data Assimilation version 3 (SODA3; current flagship release SODA3.15.2)

Available

At a glance¶

Note on period: SODA3.15.2 starts in January 1980. On 2026-10-12 the regridded 5-day files ran from 1980_01_03 to 2024_12_02 and the regridded monthly files covered 1980–2024 (one file per year). Earlier releases (3.3.2, 3.4.2, e.g. 1980–2019) cover different periods depending on their forcing.

Overview¶

SODA3 is the University of Maryland's ocean/sea ice reanalysis. It couples the MOM5 ocean model (about 1/4°, 50 levels) from GFDL CM2.5 with the SIS sea ice model and assimilates WOD temperature and salinity profiles, ICOADS in situ SST and satellite SST by optimal interpolation. A distinctive feature is a correction that reduces biases in the surface heat and freshwater fluxes. The same system has been run as an ensemble with different atmospheric forcings (MERRA-2, ERA-Interim, JRA-55, JRA55-do, ERA5 and others); the current flagship release is SODA3.15.2, forced by ERA5.

What changes with the successor¶

SODA3 (3.15.2) → SODA4 (4.15.2)¶

Transition: 2025-10

An eddy-resolving reanalysis that uses the same GFDL MOM5/SIS1 model and ERA5 forcing but raises the resolution from 1/4° and 50 levels to 1/10° and 75 levels. Data for 1980 to June 2024 are on the UMD server (native-grid ocean from 1983), and the description paper appeared as an EGUsphere preprint in October 2025 (journal publication not confirmed as of October 2026).

Sources: SODA4 portal (UMD) · Chepurin et al. (2025), SODA4 preprint, EGUsphere

Compare the two side by side

Available variables¶

Main variables from the SODA3 README and the APDRC ERDDAP copy; names are as in the netCDF files. Ocean (ocean) and sea ice (ice) fields are in separate files.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

3-D ocean (ocean, 50 levels)¶

2-D ocean (ocean)¶

Sea ice (ice)¶

Transports (transp, native grid, 10-day)¶

The full variable list is in the official documentation.

How to get the data¶

• SODA project home page (UMD) — Information page (SODA3 and SODA4 portals)
  • Version guide, how to cite, and links to the SODA3 and SODA4 portals.
• UMD data server — SODA3.15.2 — Direct HTTP(S) download No login needed
  • netCDF files in REGRIDED/ (1/2° regridded: ocean, ice) and ORIGINAL/ (native grid: ocean, ice, transport). A regridded monthly file for one year is about 2.7 GB and a 5-day file about 286 MB (about 630 MB on the native grid). The no-assimilation control run is in soda3.15.2.0/.
• UMD data server — earlier releases (soda3.3.2, soda3.4.2, etc.) — Direct HTTP(S) download No login needed
  • Folders for earlier releases remain, e.g. MERRA-2 forcing (3.3.2) and ERA-Interim forcing (3.4.2).
• APDRC ERDDAP — SODA 3.15.2 5-day 2-D variables — ERDDAP subsetting / OPeNDAP No login needed
  • University of Hawaii APDRC copy. As of October 2026 it covers only 1980-01-03 to 2022-12-23, shorter than the UMD original.
• NSF NCAR GDEX — SODA3 Ensemble Means and Standard Deviations (d650000) — Web download
  • 5-day 0.5° ensemble mean and standard deviation across forcing runs, 1980-01-03 to 2016-12-24. A different product from the individual releases.

Example code¶

Downloads one year of 1/2° regridded monthly means (about 2.7 GB) from the UMD server and opens it with xarray. Variable names follow the README.

import urllib.request
import xarray as xr

url = ("https://dsrs.atmos.umd.edu/DATA/soda3.15.2/REGRIDED/ocean/"
       "soda3.15.2_mn_ocean_reg_2020.nc")
fname = "soda3.15.2_mn_ocean_reg_2020.nc"
urllib.request.urlretrieve(url, fname)   # about 2.7 GB

ds = xr.open_dataset(fname)
print(ds["temp"])   # potential temperature (°C), 12 months × 50 levels
print(ds["ssh"])

Practical tips¶

• Always give the release number in publications (e.g. SODA3.15.2, SODA3.4.2): releases differ in forcing and period and give different results. A trailing .0 (e.g. 3.15.2.0) denotes the control run without data assimilation.
• The second number in the release name identifies the forcing: 3.3 MERRA-2, 3.4 ERA-Interim, 3.7 JRA-55, 3.12 JRA55-do, 3.15 ERA5, etc.
• The native grid is tripolar, so it is not a lat-lon grid near the Arctic. The 1/2° Mercator regridded files are easier for maps and regional means; note that temperature and salinity were remapped conservatively and velocities non-conservatively.
• There are two SODA READMEs (soda.umd.edu and www2.atmos.umd.edu/~carton) whose release lists and bulk formula descriptions differ. Confirm the forcing and period of each release from the server folders and file attributes.
• The APDRC and NCAR copies are either shorter than the UMD original (APDRC to 2022-12) or a different product (NCAR ensemble mean). Get the most recent period from the UMD server.

Notices and change history¶

References for your paper¶

Dataset citation¶

NCAR GDEX SODA3 Ensemble Means and Standard Deviations (if you used d650000) — DOI 10.5065/HBTB-R521

Reference papers¶

SODA3 reference paper (citation required by the SODA project) — DOI 10.1175/JCLI-D-18-0149.1

@article{carton2018soda3,
  author  = {Carton, James A. and Chepurin, Gennady A. and Chen, Ligang},
  title   = {{SODA3}: A New Ocean Climate Reanalysis},
  journal = {Journal of Climate},
  volume  = {31},
  number  = {17},
  pages   = {6967--6983},
  year    = {2018},
  doi     = {10.1175/JCLI-D-18-0149.1}
}

Acknowledgements¶

The SODA project asks users to identify the version used and to cite the corresponding reference paper (Carton et al. 2018 for SODA3). Data on the UMD server have no dataset DOI.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• SODA project home page
• SODA3 portal
• SODA3 README (current release)
• SODA3 README (table of releases, forcings and periods)
• Carton et al. (2018), SODA3 paper
• SODA4 portal