SRB_REL3.0_QCLW_3HRLY - GEWEX Quality-Check Longwave 3-Hourly README File 1.0 Introduction This README file provides information on the SRB_REL3.0_QCLW_3HRLY data set. The data set contains global fields of instantaneous 3-hourly values of three longwave (LW) surface radiative parameters derived with the Quality-Check LW (QCLW) 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 Science Data Center (ASDC), Science, Users and Data Services Office at: Atmospheric Science Data Center, User 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 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 three parameters in these files as follows: 1. Surface Downward Longwave Flux (DLF), 2. Surface Net Longwave Flux (NLF), and 3. Surface Longwave Cloud Radiative Forcing (LWCRF). These parameters were derived on a 3-hourly temporal resolution (i.e., a global instantaneous gridded field every 3 hours), namely, at UT hours 00, 03, 06, 09, 12 15, 18, and 21 for every day of the month. The current version of the data sets is designated as Release 3.0. It covers a period of 23 years from July 1983 to June 2006. Detailed description of the algorithm used in deriving these parameters can be found in: Gupta et al. (1992) - J. Appl. Meteor., 31, 1361-1367. Gupta (1989) - J. Climate, 2, 305-320. Wilber et al. (1999) - NASA/TP-1999-209362, 35 pp. (available on the web from http://techreports.larc.nasa.gov/ltrs/ltrs.html) 2.1 Data Quality For information on validation of these products, the user is referred to the Data Quality Summary available at: http://gewex-srb.larc.nasa.gov/ 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 became 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 longwave radiation is lower in the gap, creating an appearance of a flux discontinuity. For 3-hourly fluxes a discontinuity of magnitude less than 5 W/m**2 may appear in the Indian Ocean depending upon the meteorological conditions. 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) Surface emissivities were taken from a map developed at NASA LaRC (Wilber et al. 1999; see reference above). 2.3 Grid Description The grid on which these fluxes are originally computed is a quasi-equal-area grid consisting of 44016 cells. The cell size is 1 deg. in latitude throughout and 1 deg. in longitude between 45N and 45S. Poleward of these latitudes, the cell size is progressively increased in longitude to accommodate a sufficient number of 30 km ISCCP pixels in each cell. This grid is also called the "nested grid." A detailed description of the grid is also presented in the Data Quality Summary. The read software described below contains a subroutine to regrid the fluxes to a 1 degree latitude by 1 degree longitude equal-angle grid using replication. 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 Science Data Center User 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 These files contain an entire month of 3-hourly 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 binary data and are named according to the following convention: srb_rel3.0_qclw_3hrly_yyyymm.binary, where srb Project name, Surface Radiation Budget rel3.0 Release number for these data (Release 3.0) qclw Name of the algorithm, Quality-Check Longwave 3hrly 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 3-hourly values of the following three parameters for the whole month on the nested grid. Each file has up to 744 records; 3 records every 3 hours during the month; one for each parameter in the order they are listed below. The first 3 records are for hour 00 of day 1, the next 3 for hour 03, and so on. Name: Surface Downward LW Flux (DLF) Units: Watts per square meter Type: Real Range: 50 to 750 Fill Values: -999.0 Scale Factor: None Name: Surface Net LW Flux (NLF) Units: Watts per square meter Type: Real Range: -250 to 50 Fill Values: -999.0 Scale Factor: None Name: Surface LW Cloud Radiative Forcing (LWCRF) Units: Watts per square meter Type: Real Range: 0 to 150 Fill Values: -999.0 Scale Factor: None 5.0 Sample Read Software Description Sample read software written in Fortran-90, read_srb_rel3_qclw_3hrly.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 (srb_rel3_qclw_3hrly.nml). The input files are direct-access binary on the nested (44016 cell) 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. DLF=.true. NLF=.true. LWCRF=.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 code is that it provides one file for each parameter containing complete global fields for all 3-hourly times of the month. From these files the user should be easily able to extract a field for any time of the month and also, the values for any box or lat-lon region. 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_qclw_3hrly read_srb_rel3_qclw_3hrly.f90 The providers used a IBM XL F90 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_qclw_3hrly 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 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 hour 06 of day 14 of the month. Values for only a small lat-lon box for a single time are printed to the screen. ***************************************************************** * * * * * Data Set srb_rel3.0_qclw_3hrly Read Software * * * * Version: 1.0 * * * * Contact: Atmospheric Science Data Center * * User 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_rel3.0_qclw_3hrly_199207.binary input file is opened Variable DLF_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 311.622 305.943 305.943 317.618 317.618 lat band # 46 312.344 311.539 324.053 319.517 329.898 lat band # 47 358.951 358.556 344.426 327.131 315.679 lat band # 48 361.034 340.000 314.358 314.292 313.964 lat band # 49 328.863 316.699 320.614 324.151 323.911 lat band # 50 326.036 326.551 330.861 326.143 335.075 lat band # 51 358.127 342.728 336.332 342.477 361.960 /DLF_3hrly_199207.ascii has been written Variable NLF_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 -44.071 -50.242 -50.242 -38.993 -38.993 lat band # 46 -47.750 -48.583 -36.356 -40.913 -30.234 lat band # 47 -5.549 -5.688 -19.560 -36.414 -47.037 lat band # 48 -6.018 -26.484 -51.523 -51.021 -50.494 lat band # 49 -39.396 -51.198 -46.882 -42.701 -42.221 lat band # 50 -43.948 -43.515 -38.963 -43.095 -33.820 lat band # 51 -14.415 -30.151 -36.553 -30.292 -10.991 /NLF_3hrly_199207.ascii has been written Variable LWCRF_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 34.517 27.241 27.241 40.804 40.804 lat band # 46 30.967 32.041 46.245 42.814 53.624 lat band # 47 78.711 79.916 66.145 48.841 39.730 lat band # 48 80.827 59.684 35.880 36.242 36.817 lat band # 49 48.551 36.421 40.709 45.247 45.296 lat band # 50 44.880 44.956 50.000 46.464 56.515 lat band # 51 76.304 61.846 56.578 63.739 83.820 /LWCRF_3hrly_199207.ascii has been written 8.0 Additional Derivable Parameters It is important to keep in mind that NLF is computed as NLF = DLF - Upward LW Flux (ULF) and is, therefore, generally a negative number. Also, the three parameters provided in these files can be used to compute two additional surface LW parameters, if needed. ULF (Upward Longwave Flux) can be computed as ULF = DLF - NLF Clear-sky DLF (CSDLF) can be computed as CSDLF = DLF - LWCRF To compute these additional parameters, both quantities on the right hand side of the equations have to be available.