Surface Radiation Budget: A Long-term Global Dataset of Shortwave and Longwave Fluxes
Cite this material as: Darnell, W.L., et al., Surface Radiation Budget: A Long-term Global Dataset of Shortwave and Longwave Fluxes
http://www.agu.org/eos_elec/95206e.html
© 1996 American Geophysical Union.
W. L. Darnell and W. F. Staylor
Atmospheric Sciences Division, NASA Langley Research Center, Hampton, VA 23681, U.S.A.
N. A. Ritchey, S. K. Gupta, and A. C. Wilber
Analytical Services & Materials, Inc., Hampton, VA 23666, U.S.A.
A new global long-term dataset of monthly average surface radiation budget (SRB) parameters is now available at the NASA Langley Research Center (LaRC), Hampton, Virginia. This dataset is an extension of the LaRC component of the 46-month shortwave (SW) dataset developed by the SRB Satellite Data Analysis Center (SDAC) available from the Langley Distributed Active Archive Center (DAAC) as described by Pinker et al. [1995]. It is the product of computationally fast radiative transfer algorithms developed for deriving surface radiative fluxes on a global scale using satellite data. The primary source of input data was the International Satellite Cloud Climatology Project (ISCCP) C1 product. The dataset extends over the entire 96-month duration of the ISCCP C1 product (July 1983 to June 1991), and includes both SW and longwave (LW) surface fluxes. It should prove to be a valuable resource for a variety of climate studies as it can be used in the development of general circulation models of the atmosphere and oceans, and in the studies of surface processes and interannual climate anomalies such as El Niño/Southern Oscillation and regional floods and droughts.
Algorithms
The flux algorithms used for producing this dataset evolved from the SRB modeling effort started at the LaRC in the mid-1980s [Darnell et al., 1992; Gupta et al., 1992]. The SW algorithm, known as the "Staylor algorithm" [Darnell et al., 1992], is one of two SW algorithms chosen by the World Climate Research Program (WCRP) SRB Project for producing global insolation for the 46-month period, March 1985 through December 1988. The results of this algorithm compared well with the ground-truth, and it was also found to be insensitive to ISCCP calibration errors [Whitlock et al., 1995]. The Staylor algorithm was also selected by the Global Energy and Water-Cycle Experiment (GEWEX) SRB Project as a "quality control" algorithm, to check the performance of the "Pinker algorithm" [Pinker and Laszlo, 1992]. These algorithms will be used to produce an SW dataset covering the 12-year period July 1983 through June 1995, to meet the needs of the GEWEX participants. The LW fluxes in this dataset were produced with the "Gupta algorithm" [Gupta et al., 1992], which has been selected by the GEWEX/SRB Project for producing corresponding LW fluxes for the WCRP [WMO, 1994]. The Gupta algorithm has also undergone extensive validation and has been selected by the Clouds and the Earth's Radiant Energy System (CERES) Project as one of the two algorithms used to produce surface LW fluxes.
Input Data
Meteorological data and cloud parameters used for the computation of fluxes came from the ISCCP C1 product. The C1 product is produced globally on a 280 km x 280 km equal-area grid with 3-hour time resolution [Rossow and Schiffer, 1991]. The C1 product consists of cloud parameters derived mainly from geostationary satellite radiances, and temperature and humidity profiles obtained from operational meteorological satellites. Surface albedos for snow/ice-free land areas used for flux computations were derived from monthly average, clear-sky planetary albedos obtained from the Earth Radiation Budget Experiment (ERBE) [Barkstrom et al., 1989]. The ERBE data cover the period March 1985 through December 1988 and were used for those months. The ERBE-derived surface albedos for the above period were found to vary less than 1 percent interannually. Therefore, multi-year monthly averages of clear-sky planetary albedos from the ERBE period were used to derive the surface albedos for corresponding months outside of the ERBE period.
Results
Figures 1a and 1b show the geographical distribution of 8-year averages of downward SW (insolation) and downward LW fluxes (DLF), respectively, for July. The insolation distribution is primarily zonal, modulated by the distribution of clouds. The maxima occur over the Arctic, Greenland, and subtropical regions of the Northern Hemisphere due to the high amount of incident solar radiation and the low amount of clouds. The maxima for DLF occur over broad regions in the tropics with a gradual decrease toward the poles. The highest values occur over areas that exhibit high surface temperatures such as the subtropical deserts, and over areas where the abundance of clouds and water vapor enhance the DLF such as along the inter-tropical convergence zone (ITCZ). The lowest values for July occur over Antarctica.
Validation
Surface-measured radiative fluxes obtained from the Swiss Federal Institute of Technology's Global Energy Balance Archive (GEBA) [Ohmura and Gilgen, 1991] and NOAA's Climate Monitoring and Diagnostics Laboratory (CMDL) [Ellsworth Dutton, personal communication, 1995] were used to validate these SRB results. The GEBA data are monthly averaged downward radiative fluxes from a number of sites throughout the world, though mostly from Europe, Canada, and the former USSR. The NOAA data are monthly averaged SW and LW radiative fluxes from sites at the South Pole, Bermuda, and Kwajalein Islands.
Figure 2 shows a scatterplot of all available monthly average GEBA fluxes and the corresponding satellite-derived insolation, matched spatially as well as temporally. While the bulk of the points in this plot cluster along the line of perfect agreement, smaller groups of points do show large deviations. The causes of these deviations were investigated in detail. The group of points labeled 1 came from the South Pole comparisons, where cloud retrieval techniques have higher uncertainties and ISCCP cloud amounts are generally low. The groups labeled 2 and 3 came from the comparisons over coastal and snow/ice covered surfaces which also have higher uncertainties in cloud retrievals. The group labeled 4 came from locations in Africa and South America where large-scale biomass burning is a common occurrence. These aerosols can significantly reduce the site-measured insolation, while they are not accounted for in the model computations. Overall, the mean bias is about 5 Wm-2 and the RMS difference is about 24 Wm-2.
Figures 3a through 3c show a comparison of ground-measured and satellite-derived downward SW and LW fluxes as well as cloud amount for a site in Payerne, Switzerland. These data were provided by Thomas Konzelman of the Swiss Federal Institute of Technology. The downward SW comparison (Fig. 3a) shows general agreement, but the satellite method overestimates the SW flux during winter months. At least a part of this discrepancy may be attributed to the differences between ISCCP and site cloud amount shown in Fig. 3b. The site cloud amount is always larger than the satellite values, especially during the winter when the differences exceed 40 percent. The downward LW comparison shown in Fig. 3c also indicates that the satellite-derived results underestimate DLF, especially during the winter. When the site cloud amount was substituted in the computation of DLF, it resulted in an average increase of about 12 Wm-2.
A summary of the comparisons of the present results with GEBA and NOAA ground measurements are shown in Table 1. Most SW errors meet the same accuracy levels and regional limitations as the 46-month WCRP/SRB dataset described by Whitlock et al.[1995]. Similar LW comparisons show that fluxes are generally within 10-15 Wm-2. Larger LW errors were encountered for a very few regions where ISCCP estimates of surface temperature and water vapor have large uncertainties, such as river and mountain valleys during winter or where the ground site was not representative of the ISCCP grid cell.
Table 1. Summary of Differences between Satellite-derived and Ground Measured Fluxes from GEBA and NOAA
| Site | Downward SW | Downward LW |
|---|
| Bias | RMS | Bias | RMS |
|---|
| (Wm-2) | (Wm-2) | (Wm-2) | (Wm-2) |
|---|
| GEBA | 5.2 | 24.0 | | |
| Aswan Dam | 9.6 | 11.6 | | |
| Payerne | -12.5 | 18.4 | 16.3 | 29.9 |
| Switzerland | | | 4.4* | 18.4* |
| Kwajalein | -10.3 | 19.1 | -11.1 | 13.5 |
| Bermuda | -6.0 | 10.5 | 1.0 | 3.6 |
| South Pole | -14.7 | 26.2 | 10.0 | 15.0 |
*DLF computation using site cloud amount
Data Description and Availability
This dataset contains 96 files, one for each month from July 1983 to June 1991. Each file contains monthly average values of the following 7 parameters for each ISCCP region:
SWCS - clear-sky downward SW flux (insolation),
SWDWN - total-sky downward SW flux,
SWNET - total-sky net SW flux (absorbed),
LWCS - clear-sky downward LW flux,
LWDWN - total-sky downward LW flux,
LWNET - total-sky net LW flux, and
CP - ISCCP-derived cloud cover (percent).
In addition, there is a location identification file which contains ISCCP region numbers (1-6596), and corresponding latitude and longitude indices. File descriptions are given in the "README" file. Also given is a set of formulas that can be used to derive other SRB parameters such as surface albedo, cloud radiative forcing, and total flux parameters.
More information regarding this data can be found at the SRB Homepage at URL
'http://srb-swlw.larc.nasa.gov/'. The dataset can be obtained free of charge
from the Atmospheric Sciences Data Center at the URL http://eosweb.larc.nasa.gov/PRODOCS/srb/table_srb.html.
Requests for the PC compatible CD-ROM may be made to:
NASA Langley Atmospheric Sciences Data Center
Science, Users, and Data Services
NASA Langley Research Center
2 South Wright Street
Mail Stop 157D, Bldg 1268C
Hampton VA 23681-2199
USA
Phone: 757-864- 8656
Fax: 757-864-8807
E-mail: larc@eos.nasa.gov
Acknowledgments
The authors wish to thank T. Konzelmann of the Swiss Federal Institute of Technology and E. Dutton of NOAA/CMDL for providing the ground site data and for numerous discussions providing valuable insights. We also wish to thank C. Whitlock for providing resources for producing the CD-ROMs and W. Johnson for developing the visualization software included on the CD-ROM.
References
Barkstrom, B. R., E. F. Harrison, G. L. Smith, R. N. Green, J. F. Kibler, R. D. Cess, and the ERBE Science Team, Earth Radiation Budget Experiment archival and April 1985 results, Bull. Am. Meteorol. Soc., 70, 1254, 1989.
Darnell, W. L., W. F. Staylor, S. K. Gupta, N. A. Ritchey, and A. C. Wilber, Seasonal variation of surface radiation budget derived from ISCCP-C1 data, J. Geophys. Res., 97, 15741, 1992.
Gupta, S. K., W. L. Darnell, and A. C. Wilber, A parameterization for longwave surface radiation from satellite data: Recent improvements, J. Appl. Meteorol., 31, 1361, 1992.
Ohmura, A., and H. Gilgen, The GEBA data base, interactive applications, retrieving data, Global Energy Balance Archive, GEBA, World Climate Program Water Project A7, Report 2, Zurcher Geographische Scriften, 60 pp, 1991.
Pinker, R., and I. Laszlo, Modeling surface solar irradiance for satellite applications on a global scale, J. Appl. Meteorol., 31, 194, 1992.
Pinker, R. T., I. Laszlo, C. H. Whitlock, and T. P. Charlock, Radiative flux opens new window on climate research, Eos , 76, 145, 1995.
Rossow, W. B., and R. A. Schiffer, ISCCP cloud data products, Bull. Am. Meteorol. Soc., 72, 2, 1991.
Whitlock, C. H., T. P. Charlock, W. F. Staylor, R. T. Pinker, I. Laszlo, A. Ohmura, H. Gilgen, T. Konzelman, R. C. DiPasquale, C. D. Moats, S. R. LeCroy, and N. A. Ritchey, First global WCRP shortwave surface radiation budget data set, Bull. Am. Meteorol. Soc., 76, 905, 1995.
WMO, Report of the fifteenth session of the Joint Scientific Committee, Geneva, Switzerland, 14-18 March, 1994, WMO/TD-No. 632, 35, 1994.
Return to EES Contents
