OISST v2.1¶
NOAA 0.25-degree Daily Optimum Interpolation Sea Surface Temperature (DOISST/OISST), Version 2.1
Available
Current status
Updated daily and operating normally. Production changed in October 2021 (satellite input switched to ACSPO, v2.1a) and April 2023 (monthly time-dependent ship bias correction, v2.1b), but the product is still named v2.1. As of October 2026, NCEI has posted a notice of temporary data access delays due to its cloud migration.
At a glance¶
| Item | Details |
|---|---|
| Section | Ocean › Sea surface temperature analyses (also listed in: Sea ice › Observation-based analyses) |
| Type | Observation-based analysis |
| Domains | Ocean, Sea ice |
| Provider | NOAA National Centers for Environmental Information (NCEI) |
| Period | 1981-09 ~ present |
| Coverage | Global |
| Horizontal resolution | 1/4° regular latitude–longitude grid (global) |
| Vertical resolution | Sea surface (single level) |
| Temporal resolution | Daily (monthly means provided separately by NOAA PSL) |
| Update frequency | Daily (preliminary after about 1 day, final after about 2 weeks) |
| Licence | US Government public data — no restrictions on use; please cite the dataset DOI and the reference paper |
| Account required | No |
Note on period: A preliminary version is released about one day after the fact and replaced by the final version about two weeks later. Data before 1 January 2016 are the same as in v2.0.
How to read the resolution
- Horizontal resolution lists both the native model grid and the grid you download, as given in the official documentation. The same dataset can come on different grids from different providers or products, so check the grid of your downloaded file.
- Grid spacing is not the effective resolution. A provided grid that is finer than the native one carries no extra information.
- Intervals and whether a value is instantaneous, mean or accumulated differ between variables — see 'Available variables' below.
- The 'provided resolution' in lists and the comparison table is a simplified km/degree value for quick comparison. Use this page for exact values.
Overview¶
NOAA NCEI's daily 1/4° sea surface temperature (SST) analysis, which combines AVHRR satellite SSTs with in situ observations from ships, buoys and Argo floats into a regular global grid using optimum interpolation (OI), filling gaps to give a spatially complete map. Satellite and ship data are referenced to buoys to remove platform and sensor biases, and proxy SSTs derived from sea-ice concentration are used in the marginal ice zone. As a continuous daily record since September 1981, it is widely used for marine heatwave studies, ENSO monitoring and climatologies.
Available variables¶
Short names are the in-file variable names. Each original NCEI daily file (oisst-avhrr-v02r01.YYYYMMDD.nc) contains all four variables.
Time-stamp convention — instantaneous, mean or accumulated? — click to show
A daily analysis built from one day of observations; each value represents that day (a daily mean). In the original NCEI files the time value is 12:00 UTC, the "center time of the day", and does not denote an instantaneous value.
- NCEI describes the satellite input as daily observations averaged onto the 0.25° grid. The analysis does not resolve the diurnal cycle (day–night differences).
- In the NCEI files and ERDDAP, time is the 'Center time of the day' (e.g. 1981-09-01T12:00:00Z). The NOAA PSL yearly files stamp the same day at 00:00, so match by date when combining the two sources.
- Anomalies (anom) are relative to a daily climatology for the 1971–2000 base period. PSL also provides separate 1991–2020 climatology files.
- Proxy SSTs near sea ice use the seven-day median of daily sea-ice concentrations. The official documentation does not say how the in-file ice values are defined in time (same-day value or seven-day median).
- Preliminary data appear after about one day and final data after about two weeks, so values for the same date can change.
Source: NCEI OISST product page / ERDDAP ncdcOisst21Agg metadata
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¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Daily sea surface temperature | sst |
°C | Daily mean | |
| Daily sea surface temperature anomalies | anom |
°C | Daily mean | Daily mean SST minus the 1971–2000 daily climatology |
| Estimated error standard deviation of analysed_sst | err |
°C | Daily mean | Error estimate for that day's analysis (sst); a companion to the daily analysis rather than a separate time statistic |
Sea ice¶
| Variable | Short name | Units | Time convention | Notes |
|---|---|---|---|---|
| Sea ice concentration | ice |
fraction, 0–1 | Daily mean | The PSL files (icec, in percent) give the statistic as 'Mean' with a one-day averaging period. The official documentation does not state how the NCEI original is defined in time |
The full variable list is in the official documentation.
How to get the data¶
- NCEI direct download (daily NetCDF) — HTTPS (wget / curl) No login needed
- One file per day inside monthly folders. Preliminary files are replaced when the final versions arrive, so re-download periodically.
- NCEI THREDDS — OPeNDAP / NetCDF Subset No login needed
- NOAA PSL (yearly files) — Web download / THREDDS / OPeNDAP No login needed
- Files are bundled by variable and year (sst.day.mean.YYYY.nc, sst.day.anom.YYYY.nc, sst.day.err.YYYY.nc, icec.day.mean.YYYY.nc), which makes long periods easy to download. In the PSL files the sea-ice variable is named icec.
- AWS Open Data (NOAA CDR) — Cloud storage (S3) No login needed
- Google Cloud (NOAA CDR) — Cloud storage (GCS)
Practical tips¶
- A file for a given date first appears as a preliminary version and is replaced by the final version about two weeks later. If your analysis uses the last few weeks, re-download the final files and check your results.
- The NCEI anom field is relative to 1971–2000. For anomalies relative to 1991–2020, compute them yourself from the PSL climatology file (sst.day.mean.ltm.1991-2020.nc).
- The ice variable is the satellite sea-ice concentration used as input, a supporting field for the SST analysis. If sea ice itself is your subject, compare it with a dedicated sea-ice concentration product.
- Some evaluations find that OISST shows a larger post-1982 warming trend than other SST analyses. For trend studies, cross-check against other datasets.
Notices and change history¶
2026-10-02 · Warning · NCEI Data Access Delays (cloud migration, planned through 2026-11-30)
NCEI is moving its data and applications to the cloud, which may result in temporary data access delays. Order fulfillment services may also be degraded during this period, with empty or incomplete results. If downloads fail, use the PSL, AWS or Google Cloud copies.
2023-04-01 · Info · v2.1b — ship SST bias correction changed to a monthly time-dependent scheme
The ship SST bias correction changed from a constant to a monthly time-dependent scheme, consistent with ERSST v5, to account for ship biases that vary over time. It applies only to data produced from this date.
2021-10-01 · Info · v2.1a — satellite input switched to NOAA ACSPO SST
The satellite SST input switched from Navy SST to NOAA ACSPO SST, partly because of the deorbit of METOP-A. It applies only to data produced from this date.
2020-04-01 · Info · v2.1 released, replacing v2.0
v2.1 replaced v2.0, whose production stopped on April 26, 2020 after its input datasets were discontinued. Data from 2016 onward were improved.
References for your paper¶
Double-check before using in a paper
The citations below were compiled by the maintainer and may contain errors. Always double-check DOIs, authors, years and access-date formats against the provider's official dataset page and your journal's guidelines.
Dataset citation¶
NCEI dataset DOI — DOI 10.25921/RE9P-PT57
Huang, Boyin; Liu, Chunying; Banzon, Viva F.; Freeman, Eric; Graham, Garrett; Hankins, William; Smith, Thomas M.; Zhang, Huai-Min. (2020): NOAA 0.25-degree Daily Optimum Interpolation Sea Surface Temperature (OISST), Version 2.1. [indicate subset used]. NOAA National Centers for Environmental Information. https://doi.org/10.25921/RE9P-PT57. Accessed [date].
Show BibTeX
@misc{oisst_v21_dataset,
author = {Huang, Boyin and Liu, Chunying and Banzon, Viva F. and Freeman, Eric and Graham, Garrett and Hankins, William and Smith, Thomas M. and Zhang, Huai-Min},
title = {{NOAA} 0.25-degree Daily Optimum Interpolation Sea Surface Temperature ({OISST}), Version 2.1},
year = {2020},
publisher = {NOAA National Centers for Environmental Information},
doi = {10.25921/RE9P-PT57},
note = {Accessed DD MMM YYYY}
}
Reference papers¶
OISST v2.1 paper (citation recommended by NCEI) — DOI 10.1175/JCLI-D-20-0166.1
Huang, B., Liu, C., Banzon, V., Freeman, E., Graham, G., Hankins, B., Smith, T., Zhang, H.-M. (2021): Improvements of the Daily Optimum Interpolation Sea Surface Temperature (DOISST) Version 2.1. Journal of Climate, 34(8), 2923–2939.
Show BibTeX
@article{huang2021oisst,
author = {Huang, Boyin and Liu, Chunying and Banzon, Viva and Freeman, Eric and Graham, Garrett and Hankins, Bill and Smith, Tom and Zhang, Huai-Min},
title = {Improvements of the Daily Optimum Interpolation Sea Surface Temperature ({DOISST}) Version 2.1},
journal = {Journal of Climate},
volume = {34},
number = {8},
pages = {2923--2939},
year = {2021},
doi = {10.1175/JCLI-D-20-0166.1}
}
Original daily OISST methodology paper — DOI 10.1175/2007JCLI1824.1
Reynolds, R. W., Smith, T. M., Liu, C., Chelton, D. B., Casey, K. S., Schlax, M. G. (2007): Daily High-Resolution-Blended Analyses for Sea Surface Temperature. Journal of Climate, 20(22), 5473–5496.
Show BibTeX
@article{reynolds2007oisst,
author = {Reynolds, Richard W. and Smith, Thomas M. and Liu, Chunying and Chelton, Dudley B. and Casey, Kenneth S. and Schlax, Michael G.},
title = {Daily High-Resolution-Blended Analyses for Sea Surface Temperature},
journal = {Journal of Climate},
volume = {20},
number = {22},
pages = {5473--5496},
year = {2007},
doi = {10.1175/2007JCLI1824.1}
}
Acknowledgements¶
NCEI asks users to cite both the dataset DOI and the Huang et al. (2021) paper. If you obtained the data from NOAA PSL, also include the acknowledgement wording requested on the PSL page.
If this page helped, please acknowledge the Korean Climate Data Navigator
Please add the sentence below to the Acknowledgements of your paper.