SRB_REL2.5_QCSW_DAILY - GEWEX Quality-Check Shortwave Daily README File 1.0 Introduction This README file provides information on the SRB_REL2.5_QCSW_DAILY data set. The data set contains daily average global fields of four 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 2.2 Input Data 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 four parameters in these files as follows: 1. Clear-sky surface insolation (FCLR) 2. All-sky surface insolation (FALL) 3. Surface absorbed SW flux (FABS) 4. All-sky surface albedo (SALB) 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 2.5. 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. 2.0.1. Differences with Release-2.0 Data Set The current data set differs from the corresponding Release-2.0 data set in the following important regards: (a) Meteorological inputs for the current data set were taken from the GEOS-4 reanalysis product in place of the GEOS-1 product used for Release-2.0. (b) Broadband aerosol optical properties used for the current data set were derived using aerosol optical depths from the Model of Atmospheric Transport and Chemistry (MATCH) assimilation products and single scattering albedo and asymmetry parameter from the Optical Properties of Aerosols and Clouds (OPAC) database. Corresponding aerosol properties used for Release-2.0 processing were based on the information provided in Deepak and Gerber (1983; Report of the experts' meeting on aerosols and their climatic effects. WCP-55, 107 pp.) (c) Monthly climatological top-of-atmosphere clear-sky albedos used for the current data set were derived from 46 months (March 2000 - December 2003) of CERES data from the Terra satellite. Corresponding data used for Release-2.0 processing were based on 5 years (1985-1989) of Earth Radiation Budget Experiment (ERBE) measurements. (d) The 4-class (ocean/coast/land/desert) surface type map used for the current data set was derived from the 1/6 deg. surface type map from the International Geosphere-Biosphere Program (IGBP). Corresponding map used for Release-2.0 processing was developed for ERBE processing from older information. 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 ten years (1992-2001) 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 0.005 W/m**2 (model fluxes higher), and the root mean square difference is 42.9 W/m**2. 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. 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 Data 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 the 4-D data assimilation Goddard EOS Data Assimilation System, level-4 (GEOS-4) obtained from the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center (GSFC) (Bloom et al., 2005. Documentation and Validation of the Goddard Earth Observing System (GEOS) Data Assimilation System - Version 4 . Technical Report Series on Global Modeling and Data Assimilation 104606 , 26 http://gmao.gsfc.nasa.gov/pubs/docs/Bloom168.pdf) Column ozone values for the entire duration of this dataset (July 1983 to December 2004) were obtained primarily from the Total Ozone Mapping Spectrometer (TOMS) archive. For the early period (July 1983-November 1994), TOMS data came from NIMBUS-7 and Meteor-3 satellites. There was an interruption of about 20 months (December 1994-July 1996) after which TOMS data from EP-TOMS became available in August 1996 and continued until December 2004. All gaps in TOMS data, including those over the polar night areas every year, were filled with column ozone values 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: Paul.W.Stackhouse@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_rel2.5_qcsw_daily_yyyymm.binary, where srb Project name, Surface Radiation Budget rel2.5 Release number for these data (Release 2.5) 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 four parameters for the whole month on the nested grid. Each file has up to 124 records; 4 records for each day of the month; one for each parameter in the order they are listed below. The first 4 records are for day 1, the next 4 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 Name: All-Sky Surface Albedo (SALB) Units: Dimensionless Type: Real Range: 0 to 1 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 4 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. SALB=.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 four tables of numbers below show the values of the 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_rel2.5_qcsw_daily Read Software * * * * Version: 1.0 * * * * 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_rel2.5_qcsw_daily_199207.binary input file is opened Variable FCLR_Day = 14 lon # = 100 101 102 103 104 lat band # 45 79.450 78.812 78.812 78.591 78.591 lat band # 46 84.039 83.875 83.819 83.849 83.912 lat band # 47 89.066 89.078 89.007 89.132 89.196 lat band # 48 94.076 94.082 94.199 94.297 94.358 lat band # 49 99.054 99.160 99.341 99.474 99.459 lat band # 50 104.272 104.407 104.531 104.648 104.915 lat band # 51 109.664 109.892 110.060 110.176 110.543 file /FCLR_daily_199207.ascii has been written Variable FALL_Day = 14 lon # = 100 101 102 103 104 lat band # 45 9.567 14.394 14.394 23.825 23.825 lat band # 46 23.644 22.825 24.814 29.480 30.727 lat band # 47 35.131 44.075 34.759 39.585 38.902 lat band # 48 45.236 49.042 48.172 45.441 47.549 lat band # 49 41.211 44.459 54.648 60.012 55.626 lat band # 50 47.572 51.043 58.968 61.800 73.424 lat band # 51 62.406 75.570 82.960 78.450 85.402 file /FALL_daily_199207.ascii has been written Variable FABS_Day = 14 lon # = 100 101 102 103 104 lat band # 45 8.933 13.415 13.415 22.079 22.079 lat band # 46 21.951 21.200 23.019 27.258 28.385 lat band # 47 32.420 40.366 32.085 36.401 35.794 lat band # 48 41.531 44.880 44.120 41.716 43.576 lat band # 49 38.045 40.958 49.965 54.618 50.821 lat band # 50 43.846 46.944 53.934 56.403 66.350 lat band # 51 57.138 68.515 74.741 70.966 76.795 file /FABS_daily_199207.ascii has been written Variable SALB_Day = 14 lon # = 100 101 102 103 104 lat band # 45 0.066 0.068 0.068 0.073 0.073 lat band # 46 0.072 0.071 0.072 0.075 0.076 lat band # 47 0.077 0.084 0.077 0.080 0.080 lat band # 48 0.082 0.085 0.084 0.082 0.084 lat band # 49 0.077 0.079 0.086 0.090 0.086 lat band # 50 0.078 0.080 0.085 0.087 0.096 lat band # 51 0.084 0.093 0.099 0.095 0.101 file /SALB_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 To compute these additional parameters, both quantities on the right hand side of the equations have to be available.