Contributors: A. Velazquez Blazquez (Royal Meteorological Institute of Belgium (RMIB)), N.Clerbaux (RMIB), E. Baudrez (RMIB)
Issued by: RMIB/Clerbaux
Date: 08/07/2021
Ref: C3S_D312b_Lot1.3.8.2-v1.2_202103_PUGS_ECVEarthRadiationBudget_v1.2
Official reference number service contract: 2018/C3S_312b_Lot1_DWD/SC1
History of modifications
List of datasets covered by this document
Related documents
Acronyms
Scope of the document
This document is the Product User Guide and Specifications (PUGS) for the High-Resolution Infrared Radiation Sounder (HIRS) Outgoing Longwave radiation (OLR) Climate Data Record (CDR). This CDR is part of the Essential Climate Variable (ECV) "Earth Radiation Budget" (ERB). This PUGS aims at providing the minimum information a user should get for an appropriate use of the data available through the Copernicus Climate Data Store (CDS).
Executive summary
The monthly mean HIRS OLR CDR is produced and distributed by the National Centers for Environmental Information (NCEI) of the American National Oceanic and Atmospheric Administration (NOAA). The Principal Investigator for this product is Dr. Hai-Tien Lee from the Earth System Science Interdisciplinary Center at University of Maryland (UMD/ESSIC). The data is "brokered" in the Copernicus Climate Data Store (CDS). Therefore, this document mostly provides links to the official user documentation at NOAA/NCEI and at UMD.
The NOAA/NCEI provides the following executive summary for the version 2.7 of the CDR, extracted from the "landing page" of the HIRS OLR CDR at https://doi.org/10.7289/V5222RQP:
"This Climate Data Record (CDR) of monthly mean Outgoing Longwave Radiation (OLR) flux at the top of the atmosphere in all sky conditions is on a 2.5 degree x 2.5 degree grid with global coverage from January 1979 to the present and continuing monthly. It is derived based on the multispectral High Resolution Infrared Radiation Sounder (HIRS) OLR algorithm and other methodologies. This dataset was created from HIRS OLR retrievals from TIROS-N to NOAA-19, and MetOp-A/B satellites with inter-satellite calibration adjustments and employed the empirical diurnal model for monthly mean derivation. This version 2.7 is an upgrade from the previous version 2.2-1. The main change is in the OLR regression models and the inter-satellite calibration. The version 2.7 OLR regression models improved the retrieval consistency between variant versions of HIRS instruments, HIRS-2, 2i, 3 and 4, and in turn, the accuracy of inter-satellite calibration is significantly improved, thus eliminating the spurious trends presented in the version 2.2-1 data. The data file format is netCDF-4 with CF metadata, and it is accompanied by algorithm documentation, data flow diagram and source code for the NOAA CDR Program."
1. Product: monthly mean HIRS OLR CDR
1.1 Product description
The HIRS OLR product is based on the data acquired by the High Resolution Infrared Radiation Sounder (HIRS) instruments (Figure 1) measuring radiances in the infrared (IR).
Figure 1: HIRS instrument (left) and NOAA logo (right)
The instruments used for this CDR come from four successive versions of the instrument: HIRS/2, HIRS/2I, HIRS/3 and HIRS/4. They are installed onboard the NOAA and MetOp satellites. The Table 1 details the spacecraft’s and HIRS instrument type used as input for the HIRS OLR CDR.
Table 1: Description of the HIRS instrument type and level-1b data set coverage available for the HIRS OLR CDR production (from [D1]).
The Outgoing Longwave Radiation (OLR) is the total amount of energy emitted by the Earth and escaping toward the space. This quantity, expressed in W/m², is also called the “longwave flux” or the “thermal flux”. Together with the incoming solar radiation and the reflected solar radiation, it is a component of the Top-of-the-Atmosphere (TOA) Earth Radiation Budget (ERB).
The HIRS OLR CDR is widely used by the climate community as an important component of the ERB. The OLR can also be used as an accurate indicator of convection and is useful to diagnose the Madden-Julian Oscillation (MJO). OLR is also used for climate model evaluation. It is worth to mention that the HIRS OLR CDR is, along with the CERES products, the only data currently published in Obs4MIPS concerning the ERB.
The general characteristics of the monthly mean HIRS OLR CDR are:
Table 2: General characteristics of the product.
| |
Spatial resolution | 2.5° x 2.5° |
Grid | Regular lat-lon |
Temporal resolution | Monthly mean |
Time period | January 1979 to Feb 2021 (inclusive) |
Format | NetCDF version 4, CF compliant |
Reference level for the fluxes | 20km above mean sea level (see Loeb et al, 2002) |
Geophysical quantity | Outgoing Longwave Radiation (OLR), also known as "longwave flux" or "thermal flux" |
The following table details how this variable appears in the NetCDF files. Figure 2 provides an illustration of the OLR.
Table 3: NetCDF variables
Variables in monthly mean | olr |
long_name | NOAA Climate Data Record of Monthly Mean Upward Longwave Flux at Top of the Atmosphere |
standard_name | toa_outgoing_longwave_flux |
units | W m-2 |
Figure 2: Illustration of the monthly mean HIRS OLR v02r07 (unit is W/m²).
1.2 Target requirements
The GCOS-154 [D6] provides the following requirements for OLR:
Table 4: GCOS Target requirements
| |
Spatial resolution | 100km |
Temporal resolution | Monthly (resolving diurnal cycle) |
Accuracy | 1 W/m² |
Stability | 0.3 W/m²/decade |
In v02r07, the spatial resolution of the monthly mean HIRS OLR CDR is 2.5° x 2.5°, therefore not complying with the 100km GCOS requirement. The user requiring finer spatial resolution can consider downloading the daily mean HIRS OLR product which is provided at 1° x 1°.
In terms of temporal resolution, only monthly means are provided, without attempting to resolve the diurnal cycle. On the other hand, the HIRS OLR CDR provides an extended temporal coverage of more than 40 years.
The monthly mean HIRS OLR v02.07 product has been intensively evaluated by the Principal Investigator (PI), Dr. Hai-Tien Lee from UMD/ESSIC. The evaluation relies, partly on intercomparisons with CERES EBAF products. The accuracy of the HIRS OLR product is estimated at (better than) 1.8 W/m², at 1-standard deviation.
The stability of the product has been assessed by intercomparison with CERES (Lee, H-T, 2014a and b). The slope of the global mean OLR anomaly difference is 0.03 ± 0.09 W/m²/decade at 2 standard deviations. The stability of the product seems then to comply with the GCOS stability requirement of 0.3 W/m²/decade, at least for the 2000-onward period, when CERES data is also available.
An assessment of the accuracy of the monthly mean HIRS OLR has been done in the frame of the validation of the Climate Monitoring SAF (CM SAF) TOA Radiation GERB/SEVIRI Data Record - Edition 2 (Clerbaux, N. et al, 2017: CM SAF TOA Radiation GERB/SEVIRI Data Record - Edition 2, Satellite Application Facility on Climate Monitoring, DOI:10.5676/EUM_SAF_CM/TOA_GERB/V002, https://doi.org/10.5676/EUM_SAF_CM/TOA_GERB/V002). The reported uncertainty is about 1 W/m² for the monthly mean HIRS OLR, slightly better than the one obtained in the intercomparison with CERES EBAF (1.8 W/ m²). This difference is mainly due to the correction applied for the overall bias in the CM SAF validation [D4].
1.3 Data usage information
The HIRS OLR CDR ATBD [D2] contains a full list of assumptions and limitations. The ATBD is available at:
The “Quality Assurance Results and Summary for Monthly and Daily OLR CDR (rev.20180831).” (Lee, H-T, 2018) [D5] which is available at:
http://olr.umd.edu/References/QA_Summary_OLR-Monthly_and_Daily_CDR_20180831.pdf
2. Data access information
The monthly mean HIRS OLR data can be accessed via the Copernicus Climate Data Store (CDS, see Figure 3) at https://cds.climate.copernicus.eu
In addition to this Product User Guide and Specification (PUGS), the CDS documentation includes:
- An Algorithm Theoretical Basis Document (ATBD) [D3]
- A Product Quality Assurance Document (PQAD) [D1]
The original documentation can be accessed through two different portals:
- The official website for user documentation and data access at NOAA/NCEI: https://www.ncei.noaa.gov/products/climate-data-records/outgoing-longwave-radiation-monthly
- The HIRS OLR portal at University of Maryland (UMD) at: http://olr.umd.edu/
Figure 3: Copernicus CDS Search (https://cds.climate.copernicus.eu/cdsapp#!/search)
2.1 Product ordering process
You need to be registered and logged in to order products in the CDS. A login is provided upon registration, all products in the CDS are delivered free of charge.
2.2 Visualization tool
The data will be available in the CDS Toolbox.
2.3 Documentation
For links to the original documentation on the HIRS OLR CDR see the list of related documents on page 4 in this document.
References
Lee, H.-T., 2014a: Daily OLR CDR – Development and Evaluation. CERES Science Team Meeting, Apr 2014
Lee, H.-T., 2014b: Daily OLR Climate Data Record. EGU General Assembly, Apr 2014
Lee, H.-T., 2018: Quality Assurance Summary and Results for Monthly and Daily OLR CDR (rev.20180831).
Lee, H.-T., A. Gruber, R. G. Ellingson and I. Laszlo, 2007: Development of the HIRS Outgoing Longwave Radiation climate data set. J. Atmos. Ocean. Tech., 24, 2029–2047.
Lee, H.-T., C. J. Schreck, and K. R. Knapp, 2014: Generation of Daily OLR CDR. Eumetsat Meteorological Satellite Conference, Sep 2014
Loeb, N. G., S. Kato, and B. A. Wielicki, 2002: Defining top-of-atmosphere flux reference level for Earth Radiation Budget studies. J. Climate, 15, 3301-3309.
Schreck, C. J., H.-T. Lee and K. Knapp, 2018: HIRS Outgoing Longwave Radiation—Daily Climate Data Record: Application toward Identifying Tropical Subseasonal Variability. Remote Sens. 2018, 10, 1325
Appendix A - Specifications for Product monthly mean HIRS OLR CDR
(no specification as brokered data).
