GEWEX Quality-Check Monthly Shortwave README File 1.0 Introduction This README file provides information on the SRB_REL2_QCSW_MONTHLY data set. The data set contains monthly average global fields of twelve shortwave (SW) surface radiative parameters derived with the Quality-Check SW (QCSW) algorithm of the NASA World Climate Research Programme /Global Energy and Water-Cycle Experiment (WCRP/GEWEX) Surface Radiation Budget (SRB) Project. If users have questions, please contact the Langley Atmospheric Sciences Data Center (ASDC) Science, Users and Data Services Office at: Atmospheric Sciences Data Center Science, Users and Data Services Office Mail Stop 157D 2 South Wright Street NASA Langley Research Center Hampton, Virginia 23681-2199 U.S.A. E-mail: larc@eos.nasa.gov Phone: (757)864-8656 FAX: (757)864-8807 URL: http://eosweb.larc.nasa.gov This readme includes the following sections: 1.0 Introduction 2.0 Data Set Description 2.1 Data Quality 2.1.2. Indian Ocean Gap Artifact 2.2 Input Information 2.3 Grid Description 2.4 Points of Contact 3.0 Format and Packaging 4.0 Science Parameters Information 5.0 Sample Read Software Description 6.0 Implementing the Sample Read Software 7.0 Sample Output 8.0 Additional Derivable Parameters 2.0 Data Set Description The parameters contained in these files are: 1. TOA insolation (FTOA) 2. Clear-sky surface insolation (FCLR) 3. All-sky surface insolation (FALL) 4. Surface absorbed SW flux (FABS) 5. Surface direct SW flux (FDIR) 6. Surface diffuse SW flux (FDIF) 7. Surface PAR* flux (FPAR) 8. All-sky surface albedo (fraction) (SALB) 9. Total cloud amount (percent) (TCLD) 10. Column water vapor (gm/cm2) (CWV) 11. ERBE clear-sky surface albedo (ECSALB) 12. Clear-sky surface albedo (CSALB) These parameters were derived originally on a daily temporal resolution. Monthly averages were computed from the daily values. The current version of the data sets is identified as Release 2. Detailed description of the algorithm used in deriving these parameters can be found in: Gupta et al. (2001) - NASA/TP-2001-211272, Dec. 2001, 31 pp. (available on the web at http://techreports.larc.nasa.gov/ltrs/ltrs.html) Darnell et al. (1992) - J. Geophys. Res., 97, 15741-15760. Darnell et al. (1988) - J. Climate, 1, 820-835. 2.1 Data Quality An assessment of the quality of these monthly average fluxes was accomplished by comparisons with corresponding ground-measured fluxes over a period of four years (1992-1995) from a number of sites of the Baseline Surface Radiation Network (BSRN). From the aggregate data set for all sites and years, mean bias was determined to be about 6 W/m**2 (model - measurement), and the random error to be about +/- 21 W/m**2. It is important to keep in mind that ground-based measurements are not totally error-free. Uncertainties associated with BSRN measurements during this period are believed to be in the 5-15 W/m**2 range (Ellsworth Dutton, NOAA, BSRN Manager) depending on environmental conditions. This includes a possible thermal offset which could result in a systematic underestimation of surface measurements of up to 3% (personal communication, Rolf Philipona, World Radiation Center) depending on the atmospheric humidity and cloudiness. Thus, mean bias for the present results is well within the uncertainty for BSRN measurements. Of course, errors for individual monthly values are subject to the above-stated random error. 2.1.2. Indian Ocean Gap Artifact There is a visible and common artifact in much of the data set period, due to a lack of coverage from geostationary satellites over an area centered on 70 degrees east longitude. This situation, commonly called the Indian Ocean gap, occurs for all of the July 1983 - June 1998 time period, except for April 1988 - March 1989, when data from the INSAT satellite is available to cover the gap. In July of 1998, Meteosat-5 was moved over the gap area, eliminating the gap. When the Indian Ocean gap occurs, the gap area is covered by polar orbiting satellites, which can result in only one or two daytime overpasses per day. Geosynchronous temporal sampling during the daytime is 3-5 times per daytime depending upon the latitude (between 55 degrees North and South) and the time or year. In addition, the limbs of the geostationary satellites which bound the gap may suffer from spuriously high cloud amounts, due to large view angles. This results in an abrupt drop-off of cloud fraction in the gap as compared to the gap boundary. Downward shortwave radiation is therefore higher in the gap, creating an appearance of a flux discontinuity. All algorithms compute monthly averages from the Daily averaged fluxes. Thus, any discontinuity in the daily averaged fluxes will be averaged over the course of an entire month and are observed to persist. 2.2 Input Information Inputs to the algorithm were obtained from the following sources: Cloud parameters were derived from the International Satellite Cloud Climatology Project (ISCCP; Rossow and Schiffer, 1999,BAMS, 80, 2261-2287) DX data product. Temperature and moisture profiles were obtained from a 4-D data assimilation product provided by the Data Assimilation Office at NASA GSFC and were produced with the Goddard Earth Observing System model version 1 (GEOS-1). Column ozone for the July 1983 to November 1994 period were taken from the Total Ozone Mapping Spectrometer (TOMS) data from flights aboard Nimbus-7 and Meteor-3. Column ozone for December 1994 to October 1995 were taken from TIROS Operational Vertical Sounder (TOVS) data. Surface albedos are derived with a parameterization using monthly climatological clear-sky TOA albedos which are based on ERBE measurements during the 1985-1989 period. 2.3 Grid Description The fluxes are generated on a nested grid, which contains 44016 cells. The grid has a resolution of 1 degree latitude globally, and longitudinal resolution ranging from 1 degree in the tropics and subtropics to 120 degrees at the poles. The first cell is Latitude 89-90 degrees South, Longitude 0-120 degrees East. The cells start at the Greenwich meridian and proceed east around the globe, then shift one degree to the north. The number of cells per latitude band starting at the South Pole are: 3, 45, 45, 45, 45, 45, 45, 45, 45, 45, 90, 90, 90, 90, 90, 90, 90, 90, 90, 90, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 360, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 90, 90, 90, 90, 90, 90, 90, 90, 90, 90, 45, 45, 45, 45, 45, 45, 45, 45, 45, 3 The read software described below contains a subroutine to regrid the fluxes to 1 degree latitude by 1 degree longitude equal-angle grid using replication. 2.4 Points of Contact Scientific contact: Dr. Paul W. Stackhouse Jr. Mail Stop 420 21 Langley Boulevard NASA Langley Research Center Hampton, VA 23681-2199 U.S.A. E-mail: p.w.stackhouse@larc.nasa.gov Production Contact: Atmospheric Sciences Data Center Science, Users and Data Services Office Mail Stop 157D 2 South Wright Street NASA Langley Research Center Hampton, VA 23681-2199 U.S.A. 3.0 Format and Packaging Each file contains an entire month of monthly average global fields of the parameters described in Section 4.0 on an approximately 1 deg x 1 deg equal-area grid described in Section 2.3. The files are contain binary data and are named according to the following convention: srb_rel2_qcsw_monthly_yyyymm.binary, where srb Project name, Surface Radiation Budget rel2 Release number for these data (Release 2) qcsw Name of the algorithm, Quality-Check Shortwave monthly Time resolution of the data set yyyy 4-digit year for these data mm 2-digit month for these data binary file format 4.0 Science Parameters Information The files contain global fields of monthly averages of the following parameters on the nested grid. Each file has 12 records, containing one global field in each record. Name: Top-of-Atmosphere (TOA) Insolation (FTOA) Units: Watts per square meter Type: Real Range: 0 to 600. Fill Values: -999.0 Scale Factor: None Name: Clear-Sky Surface Downward SW Flux (FCLR) or Clear-Sky Surface Insolation Units: Watts per square meter Type: Real Range: 0 to 600. Fill Values: -999.0 Scale Factor: None Name: All-Sky Surface Downward SW Flux (FALL) or All-Sky Surface Insolation Units: Watts per square meter Type: Real Range: 0 to 500. Fill Values: -999.0 Scale Factor: None Name: Surface Absorbed SW Flux (FABS) or Surface Net SW Flux Units: Watts per square meter Type: Real Range: 0 to 500. Fill Values: -999.0 Scale Factor: None Name: Surface Direct SW Flux (FDIR) Units: Watts per square meter Type: Real Range: 0 to 500. Fill Values: -999.0 Scale Factor: None Name: Surface Diffuse SW Flux (FDIF) Units: Watts per square meter Type: Real Range: 0 to 300. Fill Values: -999.0 Scale Factor: None Name: Surface PAR* Flux (FPAR) Units: Watts per square meter Type: Real Range: 0 to 300. Fill Values: -999.0 Scale Factor: None Name: All-Sky Surface Albedo (SALB) Units: No units. It is a fraction. Type: Real Range: 0 to 1.0 Fill Values: -999.0 Scale Factor: None Name: Total Cloud Amount (TCLD) Units: No units. It is a percentage. Type: Real Range: 0 to 100. Fill Values: -999.0 Scale Factor: None Name: Column Water Vapor (CWV) Units: grams per square centimeter Type: Real Range: 0 to 8. Fill Values: -999.0 Scale Factor: None Name: ERBE Clear-Sky Surface Albedo (ECSALB) Units: No units. It is a fraction. Type: Real Range: 0 to 1.0 Fill Values: -999.0 Scale Factor: None Name: Clear-Sky Surface Albedo (CSALB) Units: No units. It is a fraction. Type: Real Range: 0 to 1.0 Fill Values: -999.0 Scale Factor: None * PAR is photosynthetically active radiation (0.4-0.7 micron) Cautionary notes: 1. Fields 5, 6, and 7 (FDIR, FDIF, and FPAR respectively) are experimental values derived within this algorithm using simple parameterizations (see Gupta et al. 2001). These fields are un-validated and therefore highly uncertain. Users are advised to be prepared to validate these parameters before use. 2. Fields 11 (ECSALB) and 12 (CSALB) were produced and archived in these files for consistency checks. The definitions of these parameters are developed in Gupta et al. (2001). ECSALB is 4 year (1985 - 1988) average albedo retrieved using ERBE TOA albedos. CSALB is the clear-sky albedo used in the calculations which is different from ECSALB under certain conditions. Users are advised to carefully review this documentation before using these products. 5.0 Sample Read Software Description Sample read software written in Fortran-90, read_qcsw_monthly.f90 was developed for reading these data. The software constitutes the name of the input data file, accesses and reads it, using the information provided in the namelist file (qcsw_monthly.nml). The input files are direct-access binary on the nested (44016 box) grid. The software reads one or more of the 3 parameter fields, regrids them to an equal-angle 1 deg x 1 deg grid, and writes them output as ascii or binary format. The choice of file format (ascii or binary) and of the location of the output files is also made through the namelist file. A sample namelist file that would be used to read the July 1992 data file and write all parameters to an ascii format output file is presented below: &time_vars yr=1992 mon=7 ascii=.true. binary=.false. path_in='**** input file path here****' path_out='**** output file path here****' little_endian=.false. FTOA=.true. FCLR=.true. FALL=.true. FABS=.true. FDIR=.false. FDIF=.false. FPAR=.false. SALB=.true. TCLD=.true. CWV=.true. ECSALB=.false. CSALB=.false. / There is a choice to convert the input fields from big endian to little endian byte order with the logical variable "little_endian" in the namelist. This applies to operating systems where byte order is stored opposite that of the Sun and SGI machines used to create the data set, such as Linux. If possible, a better choice for doing the conversion in these cases would be to use a compiler option. If using a compiler option, do not set little_endian to true. Both, input and output fields have the same orientation: they start at the Greenwich meridian-south pole and go east and north from there. A limitation of this software is that it provides a complete global field of the specified parameters in the above orientation. The user should be easily able to extract values for any box or lat-lon region from these fields. 6.0 Implementing the Sample Read Software The sample read software can be compiled with any Fortran 90 or 95 compiler. To compile: % f90 -o run_qcsw_monthly read_qcsw_monthly.f90 The providers used a NAG F95 compiler but any F90/F95 compiler should work. Edit the namelist file to select month and year to be processed, choose the parameters to be read and the format of the output file. Run the software: % run_qcsw_monthly 7.0 Sample Output When the is code run, the following information appears on the screen: The tables of numbers below show the values of each of the parameters read from the files for latitude bands 45-51 (starting at the south pole) and longitude boxes 100-104 (starting at the Greenwich meridian). Values for only a small lat-lon box are printed to the screen. ***************************************************************** * * * * * Data Set srb_rel2_qcsw_monthly Read Software * * * * Version: 1.0 * * * * Date: February 12, 2003 * * * * Contact: Atmospheric Sciences Data Center * * Science, Users and Data Services Office * * Mail Stop 157D * * 2 South Wright Street * * NASA Langley Research Center * * Hampton, Virginia 23681-2199 * * U.S.A. * * * * E-mail: larc@eos.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * ***************************************************************** srb_rel2_qcsw_monthly_199207.binary input file is opened Variable FTOA_ lon # = 100 101 102 103 104 lat band # 45 126.264 126.264 126.264 126.264 126.264 lat band # 46 132.913 132.913 132.913 132.913 132.913 lat band # 47 139.575 139.575 139.575 139.575 139.575 lat band # 48 146.245 146.245 146.245 146.245 146.245 lat band # 49 152.919 152.919 152.919 152.919 152.919 lat band # 50 159.592 159.592 159.592 159.592 159.592 lat band # 51 166.261 166.261 166.261 166.261 166.261 file FTOA_monthly_199207.ascii has been written Variable FCLR_ lon # = 100 101 102 103 104 lat band # 45 83.992 83.907 83.907 83.905 83.905 lat band # 46 88.643 88.594 88.591 88.607 88.633 lat band # 47 93.456 93.428 93.422 93.426 93.469 lat band # 48 98.358 98.331 98.308 98.342 98.369 lat band # 49 103.376 103.339 103.353 103.389 103.393 lat band # 50 108.549 108.552 108.567 108.570 108.585 lat band # 51 113.797 113.798 113.786 113.772 113.770 file FCLR_monthly_199207.ascii has been written Variable FALL_ lon # = 100 101 102 103 104 lat band # 45 42.848 40.100 40.100 43.691 43.691 lat band # 46 44.229 42.925 43.482 45.705 48.213 lat band # 47 51.243 50.907 50.843 51.355 54.060 lat band # 48 56.357 55.170 54.077 58.036 58.987 lat band # 49 59.830 56.499 60.566 65.201 64.068 lat band # 50 66.648 67.535 70.826 71.487 72.411 lat band # 51 75.747 77.841 77.494 75.475 75.061 file FALL_monthly_199207.ascii has been written Variable FABS_ lon # = 100 101 102 103 104 lat band # 45 38.429 36.287 36.287 39.500 39.500 lat band # 46 40.022 39.000 39.478 41.398 43.547 lat band # 47 46.352 46.092 46.060 46.522 48.794 lat band # 48 51.058 49.907 49.178 52.557 53.354 lat band # 49 54.286 51.423 55.006 58.938 58.040 lat band # 50 60.503 61.237 64.082 64.637 65.414 lat band # 51 68.623 70.404 70.144 68.404 67.984 file FABS_monthly_199207.ascii has been written Variable SALB_ lon # = 100 101 102 103 104 lat band # 45 0.093 0.088 0.088 0.091 0.091 lat band # 46 0.089 0.086 0.087 0.089 0.091 lat band # 47 0.090 0.090 0.089 0.090 0.093 lat band # 48 0.090 0.090 0.088 0.091 0.092 lat band # 49 0.088 0.086 0.089 0.093 0.091 lat band # 50 0.089 0.090 0.093 0.093 0.093 lat band # 51 0.092 0.093 0.093 0.091 0.091 file SALB_monthly_199207.ascii has been written Variable TCLD_ lon # = 100 101 102 103 104 lat band # 45 86.991 86.203 86.203 85.499 85.499 lat band # 46 87.930 86.895 88.306 84.812 85.484 lat band # 47 82.661 85.544 85.921 83.837 82.863 lat band # 48 84.812 87.231 83.132 82.480 80.175 lat band # 49 82.997 85.887 84.341 79.368 77.702 lat band # 50 77.184 79.032 76.378 75.067 73.320 lat band # 51 71.438 72.614 77.056 76.149 75.524 file TCLD_monthly_199207.ascii has been written Variable CWV_ lon # = 100 101 102 103 104 lat band # 45 1.233 1.242 1.242 1.247 1.247 lat band # 46 1.310 1.314 1.315 1.316 1.314 lat band # 47 1.364 1.368 1.368 1.369 1.365 lat band # 48 1.400 1.404 1.405 1.406 1.402 lat band # 49 1.411 1.414 1.415 1.416 1.414 lat band # 50 1.397 1.399 1.400 1.402 1.400 lat band # 51 1.376 1.377 1.378 1.379 1.380 file CWV_monthly_199207.ascii has been written 8.0 Additional Derivable Parameters The parameters available from these files can be used to derive additional surface SW radiative parameters. SW cloud radiative forcing (SWCRF) at the surface can be derived from all-sky and clear-sky downward fluxes as SWCRF = FALL - FCLR Upward SW flux (FUP) can be derived from all-sky downward and absorbed surface fluxes as FUP = FALL - FABS To compute these additional parameters, both quantities on the right hand side of the equations have to be available.