NOAA OLR¶

NOAA Interpolated Outgoing Longwave Radiation (PSL) and NOAA Climate Data Record of Daily/Monthly Outgoing Longwave Radiation (NCEI)

Available

At a glance¶

Note on period: The PSL Interpolated OLR daily file covers 1974-06-01 to 2022-12-31 (17,746 days). The NCEI OLR CDR starts in January 1979 for both daily and monthly products, and the daily product continues every day with about a two-day lag (the final version is replaced once a year with about a six-month lag). Daily v2.0 has 30 missing days, mostly in single-satellite periods (NOAA-6 and NOAA-9) caused by HIRS failures.

Overview¶

Gridded top-of-atmosphere outgoing longwave radiation (OLR) estimated from infrared observations on NOAA and partner polar-orbiting satellites. Low OLR in the tropics marks deep convective cloud, and because the record reaches back to the late 1970s, before CERES, it is the standard input for MJO, ENSO and monsoon convection indices. The current NCEI OLR CDR inter-calibrates HIRS, IASI and CrIS into daily (1°) and monthly (2.5°) fields, while the PSL Interpolated OLR (2.5°, 1974–2022) remains for reproducing earlier work.

What changes with the successor¶

OLR Daily CDR v1.2 (HIRS) → OLR Daily CDR v2.0 (HIRS+IASI+CrIS)¶

Transition: 2025-08

A new version that ties the IASI and CrIS hyperspectral sounders consistently to HIRS and rebuilds the HIRS regression coefficients. The monthly product moved to v3.0 on the same day, and daily v1.2 stopped at 2025-08-22.

Sources: NCEI — NOAA CDR of Daily OLR, Version 2.0 (metadata) · NCEI — Daily OLR CDR v1.2 (Version Superseded) · OLR Daily CDR User Guide (Rev 0, 2025-10-23) · OLR Monthly CDR User Guide (Rev 0, 2025-10-23)

PSL Interpolated OLR (2.5°) → NCEI OLR CDR (daily 1° / monthly 2.5°)¶

The PSL Interpolated OLR ends with 31 December 2022. For a NOAA OLR record that continues past that date, move to the OLR CDR (or the CPC Blended OLR that PSL also distributes).

Sources: PSL THREDDS — interp_OLR/olr.day.mean.nc metadata (time range 1974-06-01 to 2022-12-31) · PSL Data Notices (2026-05-07 OMI update)

Available variables¶

PSL variable names were checked in the THREDDS (OPeNDAP) structure. The NCEI CDR user guides do not give in-file variable names, so for the daily CDR olr was checked in the copy PSL distributes (olr_cdr_day/olr.day.mean.v2.nc, 1° 360×180). The variable name in the monthly CDR v3.0 (2.5°) files could not be confirmed in official documents or public copies (check your files). All OLR values are in W m-2 (written W/m^2 in PSL 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

Daily mean OLR¶

Monthly mean OLR¶

The full variable list is in the official documentation.

How to get the data¶

• NCEI — OLR Daily CDR product page (documents and download link) — Web / AWS S3 explorer (netCDF-4, one file per year)
  • The download link leads to the NOAA CDR archive (https://archive.data.noaa.gov/climatedatarecords#UMD_ESSIC/OLR_CDR/Daily/OLR-D-CDR_01B-21/).
• NCEI — OLR Monthly CDR product page — Web / AWS S3 explorer (netCDF-4, whole record in one file)
• NOAA PSL download server — OLR CDR copy (olr_cdr_day) and Interpolated OLR (interp_OLR) — Direct HTTPS download / THREDDS and OPeNDAP
  • Provides olr.day.mean.v2.nc (daily, about 3.6 GB), olr.mon.mean.v2.nc (monthly) and 1991–2020 climatologies as single files. Interpolated OLR is at https://downloads.psl.noaa.gov/Datasets/interp_OLR/ . No account is needed.

Example code¶

Opens directly through PSL OPeNDAP with no account. Interpolated OLR ends in 2022; for later dates download the OLR CDR copy from the olr_cdr_day folder and open it the same way (check its variable names).

# pip install xarray netCDF4
import xarray as xr

url = "https://psl.noaa.gov/thredds/dodsC/Datasets/interp_OLR/olr.day.mean.nc"
ds = xr.open_dataset(url)
olr = ds["olr"].sel(time=slice("2015-01-01", "2016-12-31"))
trop = olr.where(abs(olr["lat"]) <= 15, drop=True)  # 15°S–15°N regardless of latitude order
# tropical-mean OLR time series (W/m^2)
print(trop.mean(("lat", "lon")).to_series().head())

Practical tips¶

• Daily OLR CDR v1.2 and v2.0, and PSL Interpolated OLR and the OLR CDR, are different datasets. Do not splice them into one series; pick one and use it throughout.
• The most recent part of the daily OLR CDR is preliminary (file names contain -preliminary). Download again once the final version appears and re-check your results.
• The OLR CDR has no quality flags. Daily v2.0 has 30 missing days (mostly in the NOAA-6 and NOAA-9 single-satellite periods), and the guide notes an unexpectedly large CrIS inter-satellite adjustment of about 1.4 W m-2.
• Known HIRS issues listed in the guides — a one-step scan offset on NOAA-15 and -16, wrong zenith angles on NOAA-14 after March 1999, and incomplete geostationary coverage before late 1998. Take care with local analyses in those periods.
• The PSL and NCEI files differ in grid (2.5° 144×73, 1° 360×180, 2.5° 144×72) and may differ in latitude ordering. Check the order before slicing with sel(lat=slice(...)).
• Convective indices (for example the MJO OMI and RMM) change with the OLR dataset used. State the OLR dataset and version in publications.
• For the absolute energy budget use broadband radiometer data such as CERES EBAF or SYN1deg. The OLR CDR is estimated from narrowband and hyperspectral radiances, with an accuracy of about 2 W m-2 relative to CERES.

Notices and change history¶

References for your paper¶

Dataset citation¶

OLR Daily CDR v2.0 — DOI 10.25921/9pt5-by77

@misc{lee2025olrdaily,
  author    = {Lee, Hai-Tien},
  title     = {{NOAA} Climate Data Record ({CDR}) of Daily Outgoing Longwave Radiation ({OLR}), Version 2.0},
  year      = {2025},
  publisher = {NOAA National Centers for Environmental Information},
  doi       = {10.25921/9pt5-by77},
  note      = {Accessed DD MMM YYYY}
}

OLR Monthly CDR v3.0 — DOI 10.25921/edx3-v958

@misc{lee2025olrmonthly,
  author    = {Lee, Hai-Tien},
  title     = {{NOAA} Climate Data Record ({CDR}) of Monthly Outgoing Longwave Radiation ({OLR}), Version 3.0},
  year      = {2025},
  publisher = {NOAA National Centers for Environmental Information},
  doi       = {10.25921/edx3-v958},
  note      = {Accessed DD MMM YYYY}
}

OLR Daily CDR v1.2 (superseded; for reproducing earlier work) — DOI 10.7289/V5SJ1HH2

@misc{lee2011olrdaily,
  author    = {Lee, Hai-Tien and {NOAA CDR Program}},
  title     = {{NOAA} Climate Data Record ({CDR}) of Daily Outgoing Longwave Radiation ({OLR}), Version 1.2},
  year      = {2011},
  publisher = {NOAA National Climatic Data Center},
  doi       = {10.7289/V5SJ1HH2},
  note      = {Accessed DD MMM YYYY}
}

Reference papers¶

Application of the daily HIRS OLR CDR to tropical subseasonal variability — DOI 10.3390/rs10091325

@article{schreck2018hirsolr,
  author  = {Schreck, Carl J., III and Lee, Hai-Tien and Knapp, Kenneth R.},
  title   = {{HIRS} Outgoing Longwave Radiation---Daily Climate Data Record: Application toward Identifying Tropical Subseasonal Variability},
  journal = {Remote Sensing},
  volume  = {10},
  number  = {9},
  pages   = {1325},
  year    = {2018},
  doi     = {10.3390/rs10091325}
}

PSL Interpolated OLR description (citation given in the file metadata) — DOI not verified

@article{liebmann1996olr,
  author  = {Liebmann, Brant and Smith, Catherine A.},
  title   = {Description of a Complete (Interpolated) Outgoing Longwave Radiation Dataset},
  journal = {Bulletin of the American Meteorological Society},
  volume  = {77},
  pages   = {1275--1277},
  year    = {1996}
}

Acknowledgements¶

NCEI asks users to cite the version and DOI used (fill in [indicate subset used] and [access date] in the citation provided). For data obtained from PSL, acknowledge with wording such as "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¶

• NCEI — OLR Daily CDR product page
• NCEI — OLR Monthly CDR product page
• OLR Daily CDR User Guide (v2.0)
• NOAA PSL — Interpolated OLR dataset page
• NOAA PSL — CPC Blended OLR (2.5°) files