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NOAA Interpolated Outgoing Longwave Radiation (OLR)

We are now updating the data periodically. If you have acquired the files after Apr 8th 2019, please redownload them. The data for 2018 was duplicated at the end of the daily file starting after Dec 31 2018 and values for 2017 were incorrect.

Brief Description:

  • Gridded daily and monthly OLR data from NCAR with temporal interpolation. See the related Uninterpolated OLR dataset. More Details...

Temporal Coverage:

  • Monthly values for 1974/06 - 2018/12
  • Daily values for 1974/06 - 2018/12/31
  • Long Term means for Monthly and daily values for 1981-2010.

Spatial Coverage:

  • 2.5 degree latitude x 2.5 degree longitude global grid (144x73)
  • 90.0N - 90.0S 0.0E - 357.5E


  • N/A

Update Schedule:

  • Irregular, usually a few times a year.

Download/Plot Data:

Variable Statistic Level Units Download File Create Plot/Subset
OLR Daily Mean Top of Atmosphere W/m^2 olr.day.mean.nc plot
' ' Monthly Mean Top of Atmosphere W/m^2 olr.mon.mean.nc plot
' ' Daily Long Term Mean Top of Atmosphere W/m^2 olr.day.ltm.nc plot
' ' Monthly Long Term Mean Top of Atmosphere W/m^2 olr.mon.ltm.nc plot

Usage Restrictions:

  • None

Detailed Description:

  • Outgoing Longwave Radiation (OLR) data from NCAR archives, with gaps then filled with temporal and spatial interpolation. For details of the interpolation technique see Note by Liebmann and Smith (Bulletin of the American Meteorological Society, June 1996).
  • Example FORTRAN code that will read the data from the netCDF file can be found in readolr.f
  • The header has 7 values stored as short integer in variable "info": julian day, lowest day value, lowest night value, highest day value, highest night value, original number missing on day grid, original number missing on night grid.
  • However, taking a daily mean of the day and night passes, as is done for this dataset, avoids the issue of which is observed first, and serves to reduce the effective time jump that occurs at the aforementioned longitude to 12 hours.
  • Satellites and Equatorial Crossing Times:

    The following is a list of satellites used, with their initial equatorial crossing times. Whenever available, we have used the 1430 crossing times. After Mar 1 2001, we switched to NOAA16 which uses a 1350 crossing time (NOAA14 had started to suffer from severe drift). These correspond to the 'odd' numbered satellites (except for NOAA14, which was an emergency replacement for the exploded NOAA 13). The 1430 crossing times are preferred because they have been available for the longest time (John Janowiak, personal communication). Note that each of the satellites drifted considerably from its initial crossing time (see Bates et al. 1996, Journal of Climate, page 429.). Anyone discovering huge heretofore undocumented variability is advised to check the following table before publishing their result, as changing crossing times can cause spurious variability, especially over land. The difference between NOAA 14 and NOAA 12 for February, 1995 is shown here.


    DateSatelliteDaytime CrossingComments
    1974/06/01 - 1978/03/16SR series0900
    1978/03/17 - 1978/12/31  missing
    1979/01/01 - 1980/01/31Tiros N1530
    1980/02/01 - 1981/09/06NOAA 60730
    1981/09/07 - 1985/02/04NOAA 71430
    1985/02/05 - 1988/11/07NOAA 91430
    1988/11/08 - 1988/11/30NOAA 100730
    1988/12/01 - 1990/06/30NOAA 111430
    1990/07/01 - 1990/07/04NOAA 1007304 days only
    1990/07/05 - 1991/03/04NOAA 111430
    1991/03/05 - 1991/03/05NOAA 1007301 day only
    1991/03/06 - 1991/03/12NOAA 111430
    1991/03/13 - 1991/03/13NOAA 1007301 day only
    1991/03/14 - 1991/08/13NOAA 111430
    1991/08/14 - 1991/08/14NOAA 1007301 day only
    1991/08/15 - 1992/10/14NOAA 111430
    1992/10/15 - 1992/10/15NOAA 1207301 day only
    1992/10/16 - 1994/09/16NOAA 111430
    1994/09/17 - 1995/01/31NOAA 120730
    1995/02/01 - 2001/02/28NOAA 141430
    2001/03/01 - 2005/07/31NOAA 161350
    2005/09/01 - presentNOAA 1813551 day only: Dec 1 2012


  • As of March 12 1999, original pixel data was put into a 1x1 grid at NOAA's Climate Prediction Center (CPC). They then interpolated this to a 2.5x2.5 grid which is what we use. Because of the change, there are more interpolated grids than there were previously.
  • Due to satellite drift, NOAA 14 data starting 1 March 2001 have been replaced with NOAA 16 data, so it is advisable to re-acquire data beginning 1 January 2001.
  • We now retrieve data directly from NESDIS, rather than getting it through NCAR. NCAR has replaced missing days with another satellite with a different crossing time (see table above). We now interpolate gaps without replacement.

Related File Naming & Structure Information:

File Names:

  • var.time.stat.nc   (In directory: /Datasets/interp_OLR/)

OpenDap File Names:

  • https://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/interp_OLR/var.time.stat.nc   

Dataset Format and Size:

  • PSD standard NetCDF 9.8 Mbyte file for monthly file (packed).
  • PSD standard NetCDF .3 Mbyte file for monthly long term mean file (packed).
  • PSD standard NetCDF 299 Mbyte file for daily file (packed).
  • PSD standard NetCDF 7.7 Mbyte file for daily long term mean file (packed).

Missing Data:

  • Missing data is flagged with a value of 32766s.
  • Interpolated out except for 17 March to 31 December of 1978 which is unavailable due to satellite failure.


  • If you use the Interpolated OLR data in a publication, please cite Liebmann and Smith (Bulletin of the American Meteorological Society, 77, 1275-1277, June 1996).
  • Please note: If you acquire Interpolated OLR data products from PSD, we ask that you acknowledge us in your use of the data. This may be done by including text such as Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at https://www.esrl.noaa.gov/psd/ in any documents or publications using these data. We would also appreciate receiving a copy of the relevant publications. This will help PSD to justify keeping the Interpolated OLR data set freely available online in the future. Thank you!


  • Liebmann B. and C.A. Smith, 1996: Description of a Complete (Interpolated) Outgoing Longwave Radiation Dataset. Bulletin of the American Meteorological Society, 77, 1275-1277.

Original Source:

  • NCAR/NOAA (ftp ftp.cpc.ncep.noaa.gov ; cd precip/noaa* for OLR directories)


  • Physical Sciences Division: Data Management
    325 Broadway
    Boulder, CO 80305-3328