GEWEX Quality-Check Shortwave Daily README File 1.0 Introduction This README file provides information on the SRB_REL2_QCSW_DAILY data set. The data set contains daily average global fields of three 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 any 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 Infomation 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 There are a total of three parameters in these files as follows: 1. Clear-sky surface insolation (FCLR) 2. All-sky surface insolation (FALL) 3. Surface absorbed SW flux (FABS) These parameters were derived originally on a daily temporal resolution and archived at the same resolution. 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 daily 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 +/- 43 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. 2.2 Input Infomation 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 data file contains an entire month of daily 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_daily_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 daily 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 daily averages of the following three parameters for the whole month on the nested grid. Each file has up to 93 records; 3 records for each day of the month; one for each parameter in the order they are listed below. The first 3 records are for day 1, the next 3 for day 2, and so on. 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 5.0 Sample Read Software Description Sample read software written in Fortran-90, read_qcsw_daily.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_daily.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. FCLR=.true. FALL=.true. FABS=.true. / 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_daily read_qcsw_daily.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_daily 7.0 Sample Output When the is code run, the following information appears on the screen: The three tables of numbers below show the values of the three parameters contained in these files for latitude bands 45-51 (starting at the south pole) and longitude boxes 100-104 (starting at the Greenwich meridian) for day 14 of the month. Values for only a small lat-lon box for a single day are printed to the screen. ***************************************************************** * * * * * Data Set srb_rel2_qcsw_daily 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_daily_199207.binary input file is opened Variable FCLR_Day = 14 lon # = 100 101 102 103 104 lat band # 45 79.687 79.295 79.295 79.144 79.144 lat band # 46 84.314 84.182 84.138 84.096 84.146 lat band # 47 89.302 89.308 89.220 89.231 89.293 lat band # 48 94.466 94.491 94.518 94.501 94.553 lat band # 49 99.521 99.558 99.654 99.699 99.701 lat band # 50 104.632 104.638 104.653 104.637 104.800 lat band # 51 109.614 109.712 109.804 109.792 110.028 file FCLR_daily_199207.ascii has been written Variable FALL_Day = 14 lon # = 100 101 102 103 104 lat band # 45 9.596 14.482 14.482 23.992 23.992 lat band # 46 23.722 22.909 24.908 29.566 30.813 lat band # 47 35.225 44.188 34.842 39.629 38.944 lat band # 48 45.423 49.255 48.335 45.539 47.647 lat band # 49 41.406 44.638 54.820 60.148 55.761 lat band # 50 47.736 51.156 59.037 61.793 73.344 lat band # 51 62.378 75.446 82.767 78.177 85.005 file FALL_daily_199207.ascii has been written Variable FABS_Day = 14 lon # = 100 101 102 103 104 lat band # 45 8.960 13.497 13.497 22.235 22.235 lat band # 46 22.023 21.278 23.107 27.339 28.464 lat band # 47 32.506 40.470 32.162 36.442 35.833 lat band # 48 41.703 45.076 44.269 41.806 43.666 lat band # 49 38.224 41.123 50.123 54.742 50.944 lat band # 50 43.998 47.048 53.997 56.397 66.277 lat band # 51 57.112 68.403 74.568 70.719 76.437 file FABS_daily_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 All-sky surface albedo (SALB) can be derived as SALB = 1 - (FABS/FALL) To compute these additional parameters, both quantities on the right hand side of the equations have to be available.