COBE-SST2¶

Centennial in situ Observation-Based Estimates of SST, version 2

Available

At a glance¶

Note on period: When checked on 2026-10-11, the PSL SST file ran to August–September 2026. JMA posts an interim SST for the latest month first and replaces it with the final SST later. The PSL sea-ice concentration (icec) file covers only 1850 to December 2019.

Overview¶

COBE-SST2 is JMA's global sea surface temperature analysis from 1850, based on in situ observations from ICOADS. It uses a multi-time-scale analysis, in which the SST field is the sum of secular trends, interannual variations and daily changes, together with improved corrections for instrumental biases. In the Arctic and Antarctic, SSTs are estimated from sea-ice concentration using statistical relations that account for freezing points varying with climatological salinity. Alongside HadISST and ERSST, it is one of the three datasets most often compared in long-term SST studies.

What changes with the successor¶

COBE-SST2 → COBE-SST3 Planned¶

The next version in the COBE-SST series, a daily 0.25° SST analysis released with a 2025 paper. It is a research product without regular updates: the paper covers 1850–2020, and daily and monthly files to 2024 were added on the MRI server in September 2025 (the perturbed ensemble and COBE-SST3H still end in 2020). JMA's operational product remains COBE-SST2. A JMA reanalysis meeting presentation (February 2026) described COBE-SST3 as the successor to COBE-SST2, and the developers' note in the NCAR Climate Data Guide says a near-operational version extending to recent years is in development, but JMA has not formally announced that it will replace COBE-SST2.

Sources: Ishii et al. (2025) COBE-SST3, J. Meteor. Soc. Japan · NCAR Climate Data Guide — COBEv3 (with developers' notes) · JMA TCC — COBE-SST2 description · MRI COBE-SST3 data server

Compare the two side by side

Available variables¶

Variable names as in the NOAA PSL NetCDF files. The JMA NEAR-GOOS originals are text grids of integers in tenths of a degree Celsius (999 over land), and the MRI server originals are yearly GRIB2 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

Sea surface temperature¶

Sea ice (PSL, to 2019)¶

The full variable list is in the official documentation.

How to get the data¶

• JMA NEAR-GOOS — COBE-SST2 monthly mean SST — Web download (monthly text grid files) No login needed
  • The file format is described in the Readme in the same directory (Readme_cobe2_sst_glb_M). Monthly normals and standard deviations for 1991–2020 are also provided.
• NOAA PSL — COBE-SST2 (NetCDF) — Web download / THREDDS / OPeNDAP No login needed
  • The easiest option: the full SST record is in a single file, sst.mon.mean.nc. The sea-ice concentration file icec.mon.mean.nc ends in December 2019; climatology files (1981–2010, 1991–2020) are also available.
• MRI research data server (yearly GRIB2) — Web download No login needed
  • Yearly GRIB2 files and GrADS ctl files posted by the Meteorological Research Institute. Files are bundled by year, so the current year's file can lag by several months.

Practical tips¶

• Latitudes in the PSL file run north to south (89.5 to -89.5). Flip or align them before combining with other datasets.
• COBE-SST2 sea-ice concentration at PSL ends in 2019. For recent sea ice, use the OISST ice field or a satellite sea-ice concentration product.
• COBE-SST3 (0.25° daily, 1850–2024 as of October 2026) is available for research on the MRI server (climate.mri-jma.go.jp/pub/archives/Ishii-et-al_COBE-SST3/). It is worth a look for high-resolution historical analyses, but it is not updated on a regular schedule.
• The original COBE-SST (from 1891) ended in May 2023. When reproducing older papers, check which version they used.

Notices and change history¶

No notices yet.

References for your paper¶

Reference papers¶

COBE-SST2 reference paper — DOI 10.1175/JCLI-D-12-00837.1

@article{hirahara2014cobesst2,
  author  = {Hirahara, Shoji and Ishii, Masayoshi and Fukuda, Yoshikazu},
  title   = {Centennial-Scale Sea Surface Temperature Analysis and Its Uncertainty},
  journal = {Journal of Climate},
  volume  = {27},
  number  = {1},
  pages   = {57--75},
  year    = {2014},
  doi     = {10.1175/JCLI-D-12-00837.1}
}

Successor research product COBE-SST3 (for reference) — DOI 10.2151/jmsj.2025-002

Acknowledgements¶

There is no dataset DOI, so cite Hirahara et al. (2014) and state where you obtained the data (JMA or NOAA PSL). JMA's Terms of Use require a source credit such as "Source: Japan Meteorological Agency website (URL of relevant page)". If you used the PSL files, also add PSL's requested acknowledgement: "data provided by the NOAA PSL, Boulder, Colorado, USA, from their website at https://psl.noaa.gov".

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¶

• JMA TCC — COBE-SST2 description
• JMA NEAR-GOOS file format description (Readme)
• NOAA PSL — COBE-SST2 page
• NCAR Climate Data Guide — COBE-SST3
• JMA website Terms of Use