Mr. Wayne Darnell, Radiation Sciences Branch, NASA Langley Research Center
______________________________________________________________________________ | Contact 1 | Contact 2 | Contact 3 | ______________|____________________|_____________________|____________________| 2.3.1 Name |Mr. Wayne L. Darnell|Ms. Nancy Ritchey |Dr. Shashi Gupta | 2.3.2 Address |Radiation Sciences |Lockheed Engineering |Lockheed Engineering| |Branch |& Sciences Co. |& Sciences Co. | |NASA/LaRC |144 Research Dr | 144 Research Dr | City/St.|Hampton, VA |Hampton, VA |Hampton, VA | Zip Code|23681-0001 |23666 |23666 | 2.3.3 Tel. |(804)864-5685 |(804)766-9655 |(804)766-9653 | 2.3.4 Email |w.l.darnell@larc. |ritchey@solir.larc. |gupta@solir.larc. | | nasa.gov | nasa.gov | nasa.gov | ______________|____________________|_____________________|____________________| 2.4 Requested Form of Acknowledgment. Please cite the following publication when these data are used: Darnell, W. L., W. F. Staylor, S. K. Gupta, N. A. Ritchey, and A. C. Wilber, 1992. Seasonal variation of surface radiation budget derived from ISCCP-C1 data. J. Geophys. Res., 97:15741-15760. 3. INTRODUCTION 3.1 Objective/Purpose. The objective of this study was to produce daily and monthly averages of surface radiative fluxes over the entire globe for climate and other studies. 3.2 Summary of Parameters. This work was a study of radiative fluxes at the Earth's surface. The data set contains downward and net fluxes of LW and SW radiation as well as total net (LW + SW) flux. 3.3 Discussion. The surface fluxes were computed using meteorological data available from the ISCCP, TOA clear-sky albedos from ERBE, and radiation schemes developed by the prencipal investigator and his coworkers. The essentials of the method are given in Darnell et al. (1992). For greater details of the methodology the user is referred to Darnell et al. (1988), Gupta (1989), Gupta et al. (1992), and Whitlock et al. (1993). 4. THEORY OF MEASUREMENTS No measurements were made directly by the investigators. The necessary inputs all came from satellite sources. ISCCP-C1 data sets were chosen as inputs here because most of the meteorological data for these data came from operational satellite sources. Also, the cloud parameters derived by ISCCP are about the best currently available. The data coverage is global. For an explanation of the ISCCP C1 data see Brest and Rossow (1992), Desormeux et al. (1993), Rossow and Garder (1993a), Rossow and Garder (1993b), Rossow et al. (1993), Rossow and Schiffer (1991), Schiffer and Rossow (1983), Schiffer and Rossow (1985). The angular models used in the inference model are described in Suttles et. al., (1988). 5. EQUIPMENT The basic instruments which made the measurements for ISCCP were the visible and infrared imaging radiometers on-board geostationary and polar Sun- synchronous satellites which were operational during the data period. However for the SRB project, only the final ISCCP-C1 products were used. The details of the various satellite missions are beyond the scope of the SRB project. Therefore, the various subsections of Sec. 5 do not apply to this project. 5.1 Instrument Description. Not applicable. 5.1.1 Platform (Satellite, Aircraft, Ground, Person...). Not applicable. 5.1.2 Mission Objectives. Not applicable. 5.1.3 Key Variables. Not applicable. 5.1.4 Principles of Operation. Not applicable. 5.1.5 Instrument Measurement Geometry. Not applicable. 5.1.6 Manufacturer of Instrument. Not applicable. 5.2 Calibration. For an explanation of the ISCCP C1 data calibration, see Brest and Rossow (1992), Desormeux et al. (1993). 5.2.1 Specifications. Not applicable. 5.2.1.1 Tolerance. Not applicable. 5.2.2 Frequency of Calibration. Not applicable. 5.2.3 Other Calibration Information. Not applicable. 6. PROCEDURE 6.1 Data Acquisition Methods. The data sets described in this document were acquired by the Goddard Distributed Active Archive Center (GDAAC) from W. L. Darnell NASA Langley Research Center. The ISCCP-C1 data are currently available from User and Data Services at the Langley DAAC, NASA Langley Research Center. 6.2 Spatial Characteristics. The original data was supplied on an ISCCP equal-area grid that had a spatial resolution of 280 by 280 km. The Goddard DAAC converted this data to a 1 x 1 degree lat/lon equal-area grid (see section 9.3.1 for details). 6.2.1 Spatial Coverage. The coverage is global. Data in each file are ordered from North to South and from West to East beginning at 180 degrees West and 90 degrees North. Point (1,1) represents the grid cell centered at 89.5 N and 179.5 W (see section 8.4). 6.2.2 Spatial Resolution. The data are given in an equal-angle lat/long grid that has a spatial resolution of 1 X 1 degree lat/long. 6.3 Temporal Characteristics. 6.3.1 Temporal Coverage. January 1987 through December 1988. 6.3.2 Temporal Resolution. Monthly mean. 7. OBSERVATIONS 7.1 Field Notes. Not applicable. 8. DATA DESCRIPTION 8.1 Table Definition With Comments. Not applicable. 8.2 Type of Data. -------------------------------------------------------------------------------- | 8.2.1 | | | | |Parameter/Variable Name | | | | -------------------------------------------------------------------------------- | | 8.2.2 | 8.2.3 | 8.2.4 | 8.2.5 | | |Parameter/Variable Description |Range |Units |Source | -------------------------------------------------------------------------------- |SUR_LWDN | | | | | |Surface longwave downward |min = 50., |[Watts] |Computed | | |radiation flux |max = 750., |[m^-2] |from | | | |missing = -999.| |ISCCP-C1 | -------------------------------------------------------------------------------- |SUR_LWNT | | | | | |Surface longwave net radiation |min = -250., |[Watts] |computed | | |flux |max = 50., |[m^-2] |from | | | |missing = -999.| |ISCCP-C1 | -------------------------------------------------------------------------------- |SUR_SWDN | | | | | |Surface shortwave downward |min = 0., |[Watts] |Computed | | |radiation flux (insolation) |max = 500., |[m^-2] |from | | | |missing = -999.| |ISCCP-C1 | -------------------------------------------------------------------------------- |SUR_SWNT | | | | | |Surface shortwave net radiation |min = 0., |[Watts] |Computed | | |flux (absorbed) |max = 500., |[m^-2] |from | | | |missing = -999.| |ISCCP-C1 | -------------------------------------------------------------------------------- |SUR_TONT | | | | | |Surface total net radiation flux |min = -100., |[Watts] |Computed | | |(LW_NET + SW_NET) |max = 300., |[m^-2] |from | | | |missing = -999.| |ISCCP-C1 | -------------------------------------------------------------------------------- 8.3 Sample Data Base Data Record. Not applicable. 8.4 Data Format. The CD-ROM file format is ASCII, and consists of numerical fields of varying length, which are space delimited and arranged in columns and rows. Each column contains 180 numerical values and each row contain 360 numerical values. Grid arrangement ARRAY(I,J) I = 1 IS CENTERED AT 179.5W I INCREASES EASTWARD BY 1 DEGREE J = 1 IS CENTERED AT 89.5N J INCREASES SOUTHWARD BY 1 DEGREE 90N - | - - - | - - - | - - - | - - | (1,1) | (2,1) | (3,1) | 89N - | - - - | - - - | - - - | - - | (1,2) | (2,2) | (3,2) | 88N - | - - - | - - - | - - - | - - | (1,3) | (2,3) | (3,3) | 87N - | - - - | - - - | - - - | 180W 179W 178W 177W ARRAY(360,180) 8.5 Related Data Sets. Surface and TOA shortwave radiation and photosynthetically active radiation data set's. (on this CD-ROM.) ISCCP-C1 data, see section 14.3. ERBE-S4 data, see section 14.3. Surface Shortwave Down Radiation NASA/LaRC, ECMWF Hybrid (on CD-ROM Vol. 5). Surface Longwave Down Radiation NASA/LaRC, ECMWF Hybrid (on CD-ROM Vol. 5). 9. DATA MANIPULATIONS 9.1 Formulas. For various formulas and details of the algorithm, the user is referred to Darnell et al. (1992). 9.1.1 Derivation Techniques/Algorithms. The LW technique: The LW radiative fluxes (both LWDN and LWNT) are computed using a fast parameterization which is based on detailed radiative transfer computations (Gupta 1989; Gupta et al. 1992). The inputs for the computation are taken from the ISCCP-C1 data sets. LWDN is computed as LWDN = F1 + F2 * AC, where F1 is the clear-sky LWDN, F2 is the cloud forcing factor, and AC is the fractional cloud cover. LWNET is computed as LWNT = LWDN - SIGMA * TS^4, where SIGMA is the Stefan-Boltzman constant (=5.67E-08 [W][m^-2] [K^-4]), and TS is the surface temperature. Details of the development and application of the parameterizations of F1 and F2 in terms of the meteorological parameters available from ISCCP-C1 data are given in Gupta (1989) and Gupta et al. (1992). A very brief description of the parameterizations is presented here. The clear-sky LWDN (F1) is computed as F1 = ( A0 + A1 * V + A2 * V^2 + A3 * V^3 ) * TE^3.7, where V = ln W, and W is the total water vapor burden of the atmosphere. TE is an effective emitting temperature of the lower troposphere, and is computed as TE = KS*TS + K1*T1 + K2*T2, where TS is the surface temperature, T1 is the mean temperature of the first layer in the ISCCP-C1 data (surface to 800[mb]), and T2 is the same for the second layer (800[mb] to 680[mb]). KS, K1, and K2 are weighting factors with values of 0.60, 0.35, and 0.05 respectively. The regression coefficients A0, A1, A2, and A3 have the following values: A0 = 1.791E-07, A1 = 2.093E-08, A2 = -2.748E-09, A3 = 1.184E-09. The cloud forcing factor (F2) is computed as F2 = TCB^4 / ( B0 + B1 * WC + B2 * WC^2 + B3 * WC^3 ), where TCB is the cloud-base temperature, WC is the water vapor burden below the cloud base, and B0, B1, B2, and B3 are regression coefficients with the following values: B0 = 4.990E+07, B1 = 2.688E+06, B2 = -6.147E+03, B3 = 8.163E+02. All fluxes represented here are in [W][m^-2], temperatures in deg. K, and water vapor burdens in [kg][m^-2]. Cloud-base pressure is obtained by combining cloud-top pressure (available from ISCCP-C1 data) with climatological estimates of cloud thickness which depend upon cloud height and latitude. TCB and WC are computed from the available ISCCP-C1 data using the procedure described in Gupta (1989). The above equation for F2 is used as such when the pressure difference between the surface and cloud base is greater than 200 [mb]. When the pressure difference is greater than or equal to 200 [mb], a modified form of this equation, as described in Gupta et al. (1992), is used. The SW technique: The shortwave algorithm was developed at NASA Langley Research Center by W. F. Staylor. It is a parameterized/physical model that utilizes ISCCP-C1 data (Rossow and Schiffer, 1991) as its primary input data. The current model is a modified version of an earlier model by Darnell et al. (1988). A recent application of the method is given in Darnell et al. (1992). Instantaneous downward SW at the surface (insolation) can be estimated using the model presented in Darnell et al. (1988). Downward SW flux at the surface is the product of insolation at the TOA, clear-sky atmospheric transmittance and cloud transmittance. Daily insolation requires time integration of the instantaneous values from sunrise to sunset. Insolation at the TOA is a product of the cosine of the solar zenith angle and the distance-corrected solar flux, which is calculated daily using 1365 [W][m^-2] as the solar flux and 1[astronomical units] as the Earth-Sun distance. Atmospheric transmittance is a function of surface pressure, surface albedo, aerosols, and the effective clear-sky atmospheric optical depth. The first three terms account for the atmospheric backscatter of surface reflected rays. The effective clear-sky atmospheric optical depth is a vertical attenuation factor for solar energy and it is the sum of all absorption and scattering processes. These processes include absorption and scattering due to gases and aerosols. The broadband absorption due to water vapor and ozone, and Rayleigh attenuation are estimated using Lacis and Hansen (1974). The broadband absorption due to oxygen and carbon dioxide are approximated using Yamamoto (1962). Aerosol attenuation is based on World Climate Program models (World Climate Research Program, 1983) and is a function of aerosol optical depth, an asymmetry factor and the single- scattering albedo. It should be noted that the Rayleigh and aerosol attenuation terms are concerned only with backscattering and/or absorption, but not with forward scattering of flux which reaches the surface. Cloud transmittance is based on a threshold technique which relates boundary values of TOA reflectances for overcast and clear-sky conditions and actual measured conditions (from ISCCP). Overcast reflectances are estimated from a model by Staylor (1985) using the cosines of viewing zenith angle and solar zenith angle, and overcast coefficients. These coefficients are determined monthly for each ISCCP satellite using data for non-snow covered, totally overcast regions having mean cloud optical depths within the top 5 percentile of all observations. Clear-sky reflectances are determined by one of several methods depending on the snow cover and surface type. Over oceans, the cosines of viewing zenith angle and solar zenith angle, along with clear-sky coefficients are used. These coefficients are determined for totally-clear oceans for each satellite every month. For snow- free land regions or land regions in which the snow cover does not fluctuate by more than 10 percent during the month, daily TOA clear-sky reflectance values are computed from the clear-sky pixels. The monthly minimum value is used for the entire month. If the snow cover changes by more than 10 percent during the month (determined for 5-day intervals), then the above procedure is applied to the 5-day periods. Measured instantaneous reflectances are the pixel-weighted average of the clear and cloudy reflectances. If no value exists for a day (occurs most frequently in polar regions), a fill value is provided by one of two methods. If a value exists for a longitudinally adjacent region for that day, it is used. If it does not exist, then the previous day's value is used. This procedure is expanded spatially, then temporally until a non-fill value is found. Daily surface albedo for all-sky conditions is a function of the daily overcast albedo, the daily clear-sky albedo and cloud transmittance. Data from Budyko (see Payne 1972) and Ter-Markariantz (see Kondratyev 1973) were used to estimate clear-sky surface albedos over oceans. Estimates of daily overcast albedos over oceans are based on the fact that under overcast conditions the effective zenith angle of the diffuse rays is about 53 [degrees] for all zenith angles (cosine = 0.6) and therefore is a constant value of 0.065. Clear-sky ERBE TOA albedos were used to estimate clear-sky surface albedos over land. This approach avoided the need for spectral conversions from narrowband to broadband and from radiances to albedos (Staylor and Wilber 1990). Overcast albedos over land are estimated using the clear-sky land albedo and the cosine of the solar zenith angle. Total net flux: Total net flux is the sum of net LW flux and net SW flux. For further information, the user is referred to Darnell et al. (1992). 9.2 Data Processing Sequence. Details of processing are discussed in Darnell et al. (1992). 9.2.1 Processing Steps and Data Sets. Details of processing are discussed in Darnell et al. (1992). 9.2.2 Processing Changes. This is the first version of this data set. 9.3 Calculations. The user is referred to Darnell et al. (1992). 9.3.1 Special Corrections/Adjustments. Below is a description of the re-gridding process done by the Goddard DAAC: Physical Lay Out of Original Data: 24 files, with each file representing the monthly means for the entire globe. Within each file, each line consists of a grid index, latitude index, longitude index, followed by the five radiation parameters. The data are gridded using the ISCCP method of equal area gridding. The equal area map is defined by the area of a 2.5 x 2.5 degree cell at the equator. There are 6596 cells in this map grid. All map cells are determined by a constant 2.5 degree increment in latitude and a variable longitude increment. The longitude increment is selected to provide an integer number of cells in a latitude zone and to give a cell area as close to that of the equatorial cell as possible. Logical Lay Out of Original Data: Within each file, the data start at the 0 deg. longitude, and -90 deg. latitude, progressing eastward to 360 deg. longitude, and then northward to 90 deg. latitude. Processing Steps done by the Goddard DAAC: Regrid each latitude and longitude band of data by implementing the following steps: 1) Replicated every data value in each latitude band 360 times, assigning them to a temporary array. For latitude band #1, there were 3 values, each value is replicated 360 times producing a temporary array of 1080 data values. The number of original values in a latitude band increases as you move toward the equator, where there were 144 data values. If the latitude band originally had 144 data values, this would also be replicated 360 producing a temporary array of 51840 data values. 2) For latitude band #1 the first three (temporary array) data values are summed and then divided by the number of original values (3) for that latitude band. This was repeated 359 more times, for every three (temporary array) data values, in affect performing a linear interpolation of the data within the latitude band. If the latitude band had 144 data values, every 144 (temporary array) data values would be summed and then divided by 144. 3) Step 1 and 2 were repeated until all latitude bands have been interpolated. 4) A similar method, discussed above, was used for regridding each longitude band of data. The difference was that the number of data values in each longitude band did not vary (there were always 144 data values), and the replication was 180. 5) The resulting array of data values were then split and shifted from 0 longitude -> 360 longitude to -180 longitude -> 180 longitude. 6) These data were then flipped from -180 longitude, -90 latitude to -180 longitude, 90 latitude. 9.4 Graphs and Plots. The user is referred to Darnell et al. (1992). 10. ERRORS 10.1 Sources of Error. Errors in the fluxes come from the radiation modeling and from the meteorological data. Modeling errors are systematic and are generally small. Errors from meteorological data are both random and systematic. For a detailed analysis of errors the reader is referred to Gupta et al. (1993). 10.2 Quality Assessment. 10.2.1 Data Validation by Source. The SW fluxes obtained with this model were validated with insolation measurements obtained from a large number of sites. See Darnell et al. (1988) for details. The LW fluxes obtained with the model used here were validated with surface measurements from 4 sites in the United States. See Darnell et al. (1986) for details of LW validation. 10.2.2 Confidence Level/Accuracy Judgment. While larger sources of errors are identified and quantified, smaller sources, e.g. the occurrence of fog, are difficult to quantify. These definitely contribute some to the bias in the fluxes. 10.2.3 Measurement Error for Parameters and Variables. Random errors on monthly average SW and LW fluxes are about 10-12 [W] [m^-2]. No estimates are available for systematic errors. 10.2.4 Additional Quality Assessment Applied. None. 11. NOTES 11.1 Known Problems With The Data. There are no known gaps in these data sets. 11.2 Usage Guidance. Errors in polar regions may be larger than those quoted in Section 10. 11.3 Other Relevant Information. None. 12. REFERENCES 12.1 Satellite/Instrument/Data Processing Documentation. ERBE Data Management Team, 1991. "ERBE Data Management System, The Regional, Zonal and Global Averages, S-4 Users Guide." NASA/Langley, Hampton, Virginia. Rossow, W. B. L. C. Garder, P. J. Lu and A. Walker, 1988. International Satellite Cloud Climatology Project (ISCCP): Documentation of cloud data, Tech. Doc. WMO/TD 266, 75 pp., World Climate Research Programme, Geneva. World Meteorological Organization (WMO), 1984. Solar radiation and radiation balance data, July 1983, World Radiat. Data Center, Voeikov Main Geophys. Observ., St. Petersburg, Russia. 12.2 Journal Articles and Study Reports. Brest, C.L., and W.B. Rossow, 1992. Radiometric calibration and monitoring of NOAA AVHRR data for ISCCP. Int. J. Remote Sensing, 13:235-273. Darnell, W. L., S. K. Gupta, and W. F. Staylor, 1986. Downward longwave surface radiation from Sun-synchronous satellite data: Validation of methodology. J. Clim. Appl. Meteorol., 25:1012-1021. Darnell, W. L., W. F. Staylor, S. K. Gupta, and F. M. Denn, 1988. Estimation of surface insolation using Sun-synchronous satellite data. J. Climate, 1:820-835. Darnell, W. L., W. F. Staylor, S. K. Gupta, N. A. Ritchey, and A. C. Wilber, 1992. Seasonal variation of surface radiation budget derived from ISCCP-C1 data. J. Geophys. Res., 97:15741-15760. Desormeaux, Y., W.B. Rossow, C.L. Brest and G.G. Cambell, 1993. Normalization and calibration of geostationary satellite radiances for ISCCP. J. Atmos. Ocean Tech., 10:304-325. Gupta, S. K., 1989. A parameterization for longwave surface radiation from Sun-synchronous satellite data. J. Climate, 2:305-320. Gupta, S. K., W. L. Darnell, and A. C. Wilber, 1992. A parameterization of longwave surface radiation from satellite data: Recent improvements. J. Appl. Meteorol., 31:1361-1367. Gupta, S. K., A. C. Wilber, W. L. Darnell, and J. T. Suttles, 1993. Longwave surface radiation over the globe from satellite data: An error analysis. Int. J. Remote Sens., 14:95-114. Lacis, A. A. and J. E. Hansen, 1974. A parameterization for the absorption of solar radiation in the earth's atmosphere. J. Atmos. Sci., 31:118-133. Kondratyev, K. Y., 1973. Radiation characteristics of the atmosphere and the Earth's surface. NASA TTF-678, 580pp. Payne, R. E., 1972. albedo of the sea surface. J. Atmos. Sci., 29:959-970. Rossow,W.B., and L.Garder, 1984. Selection of a map grid for data analysis and archival. J.Climate and Appl. Meteor., 23:1253-57. Rossow, W. B., and R. A. Schiffer, 1991. ISCCP cloud data products. Bull. Amer. Meteor. Soc., 72:2-20. Rossow, W.B., and L.C. Garder, 1993a. Cloud detection using satellite measurements of infrared and visible radiances for ISCCP. J. Climate, 6:2341-2369. Rossow, W.B., and L.C. Garder, 1993b. Validation of ISCCP cloud detections. J. Climate, 6:2370-2393. Rossow, W.B., A.W. Walker and L.C. Garder, 1993: Comparison of ISCCP and other cloud amounts. J. Climate, 6:2394-2418. Staylor, W. F., 1985. Reflection and emission models for clouds derived from Nimbus 7 Earth radiation budget scanner measurements. J. Geophys. Res., 90:8075-8079. Staylor, W. F., and A. C. Wilber, 1990. Global surface albedos estimated from ERBE data. Proceedings of AMS Conf. on Atmospheric Radiation, July 23-27, 1990, San Francisco, CA, pp 231-236. Whitlock, C. H., T. P. Charlock, W. F. Staylor, R. T. Pinker, I. Laszlo, R. C. DiPasquale, and N. A. Ritchey, 1993. WCRP Surface Radiation Budget Shortwave Data Product Description - Version 1.1. NASA Technical Memo 107747, NTIS, Springfield, Virginia. World Climate Research Program, 1983. Experts meeting on aerosols and their climate effects. A. Deepak and H. E. Gerber editors, WCP-55, 107 pp. Yamamoto, G., 1962. Direct absorption of solar radiation by atmospheric water vapor, carbon dioxide, and molecular oxygen. J. Atmos. Sci., 19:182-188. 12.3 Archive/DBMS Usage Documentation. Contact the EOS Distributed Active Archive Center (DAAC) at NASA Goddard Space Flight Center (GSFC), Greenbelt Maryland (see Section 13 below). Documentation about using the archive or information about access to the on-line information system is available through the GSFC DAAC User Services Office. 13. DATA ACCESS 13.1 Contacts for Archive/Data Access Information. GSFC DAAC User Services NASA/Goddard Space Flight Center Code 902.2 Greenbelt, MD 20771 Phone: (301) 286-3209 Fax: (301) 286-1775 Internet: daacuso@eosdata.gsfc.nasa.gov 13.2 Archive Identification. Goddard Distributed Active Archive Center NASA Goddard Space Flight Center Code 902.2 Greenbelt, MD 20771 Telephone: (301) 286-3209 FAX: (301) 286-1775 Internet: daacuso@eosdata.gsfc.nasa.gov 13.3 Procedures for Obtaining Data. Users may place requests by accessing the on-line system, by sending letters, electronic mail, FAX, telephone, or personal visit. Accessing the GSFC DAAC Online System: The GSFC DAAC Information Management System (IMS) allows users to ordering data sets stored on-line. The system is open to the public. Access Instructions: Node name: daac.gsfc.nasa.gov Node number: 192.107.190.139 Login example: telnet daac.gsfc.nasa.gov Username: daacims password: gsfcdaac You will be asked to register your name and address during your first session. Ordering CD-ROMs: To order CD-ROMs (available through the Goddard DAAC) users should contact the Goddard DAAC User Support Office (see section 13.2). 13.4 GSFC DAAC Status/Plans. The ISLSCP Initiative I CD-ROM is available from the Goddard DAAC. 14. OUTPUT PRODUCTS AND AVAILABILITY 14.1 Tape Products. None. 14.2 Film Products. None. 14.3 Other Products. ISCCP-C1 and ERBE-S4 data, can be acquired from the Langley DAAC. The Langley DAAC User and Data Services Office may be contacted as follows: User and Data Services Langley DAAC Mail Stop 157B NASA Langley Research Center Hampton, VA 23681-0001 Telephone: (804) 864-8656 FAX: (804) 864-8807 e-mail: userserv@eosdis.larc.nasa.gov 15. GLOSSARY OF ACRONYMS CD-ROM Compact Disk (optical), Read Only Memory DAAC Distributed Active Archive Center ERBE Earth Radiation Budget Experiment EOS Earth Observing System GCM General Circulation Model of the atmosphere GSFC Goddard Space Flight Center ISCCP International Satellite Cloud Climatology Project IDS Inter Disciplinary Science ISLSCP International Satellite Land Surface Climotology Project LaRC Langley Research Center LW Longwave Radiation LWDN Longwave Radiation Downward Flux LWNT Longwave Net Radiation Flux NASA National Aeronautics and Space Administration PI Principal Investigator SRB Surface Radiation Budget SW Shortwave Radiation SWDN Shortwave Radiation Downward Flux SWNT Shortwave Net Radiation Flux TOA Top-Of-Atmosphere TONT Total Net Radiation Flux