SRB_REL2.5_QCLW_3HRLY_MONTHLY - GEWEX Quality-Check Longwave Monthly Averaged 3-Hourly (Diurnal) README File 1.0 Introduction This README file provides information on the SRB_REL2.5_QCLW_3HRLY_MONTHLY data set. The data set contains monthly average/3-hourly (also called diurnally-resolved monthly average or just 'diurnal' for brevity) global fields 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 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 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 originally 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 3-hourly values were used to compute monthly averages separately for each of the 8 GMT hours. 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. (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) 2.0.1. Differences with Release-2.0 Data Set The only important difference between the current data set and the corresponding Release-2.0 data set is the use of GEOS-4 meteorological inputs for the current data set in place of GEOS-1 for Release-2.0. 2.1 Data Quality An assessment of the quality of these monthly average/3-hourly 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 about 7.4 W/m**2 (2.5%, model fluxes higher), and the root mean square difference is 19.5 W/m**2 (6.6%). Uncertainties associated with operational BSRN measurements during this period are believed to be about +/- 5 W/m**2 (Ellsworth Dutton, NOAA, BSRN Manager). These errors should be considered very reasonable and the users also need to keep in mind that ground-based measurements are not totally error-free. 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 longwave radiation is lower in the gap, creating an appearance of a flux discontinuity. For 3-hourly/monthly averaged fluxes a discontinuity of magnitude less than 5 W/m**2 for surface fluxes may appear in the Indian Ocean gap region. 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 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 file contains an entire month of monthly-average/3-hourly global fields (resolved at 8 times) 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_qclw_3hrlymonthly_yyyymm.binary, where srb Project name, Surface Radiation Budget rel2.5 Release number for these data (Release 2.5) qclw Name of the algorithm, Quality-Check Longwave 3hrlymonthly Indicates 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 diurnally-resolved monthly averages of the three parameters on the nested grid. Each file has 24 records, 3 records for each of the 8 times containing global fields the 3 parameters in the order listed below. Name: Surface Downward LW Flux (DLF) Units: Watts per square meter Type: Real Range: 50 to 650 Fill Values: -999.0 Scale Factor: None Name: Surface Net LW Flux (NLF) Units: Watts per square meter Type: Real Range: -180 to 20 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_qclw_3hrlymonthly.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 (qclw_3hrlymonthly.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. 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 software is that it provides a complete global field of the specified parameters in the above orientation for all 8 times of the day. The user should be easily able to extract values for any box or lat-lon region from these fields for any time of the day. 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_3hrlymonthly read_qclw_3hrlymonthly.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_qclw_3hrlymonthly 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) at hour 06. Values for only a small lat-lon box are printed to the screen. ***************************************************************** * * * * * Data Set srb_rel2.5_qclw_3hrlymonthly 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_qclw_3hrlymonthly_199207.binary input file is opened Variable DLF_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 309.355 313.526 313.526 316.296 316.296 lat band # 46 317.440 319.411 322.231 314.202 321.536 lat band # 47 320.236 323.223 323.075 324.640 318.815 lat band # 48 329.224 327.196 327.034 325.352 322.629 lat band # 49 328.886 331.666 327.865 324.737 323.865 lat band # 50 331.249 331.732 324.300 328.792 325.108 lat band # 51 330.080 326.309 331.835 332.692 333.320 file /DLF_3hrlymonthly_199207.ascii has been written Variable NLF_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 -45.690 -42.313 -42.313 -40.054 -40.054 lat band # 46 -42.027 -40.215 -37.646 -45.722 -38.256 lat band # 47 -43.130 -39.985 -40.019 -38.214 -43.464 lat band # 48 -36.703 -38.350 -38.127 -39.232 -41.207 lat band # 49 -38.494 -35.437 -38.732 -41.161 -41.348 lat band # 50 -37.841 -37.333 -44.366 -39.374 -42.600 lat band # 51 -41.165 -45.253 -39.780 -38.751 -38.156 file /NLF_3hrlymonthly_199207.ascii has been written Variable LWCRF_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 50.981 54.416 54.416 56.259 56.259 lat band # 46 54.185 56.308 59.245 51.266 58.332 lat band # 47 53.411 56.840 57.036 58.876 53.418 lat band # 48 60.258 58.797 59.100 57.880 55.593 lat band # 49 58.670 61.847 58.396 55.729 55.154 lat band # 50 59.833 60.446 53.324 58.135 54.378 lat band # 51 57.683 53.697 59.164 59.982 60.367 file /LWCRF_3hrlymonthly_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 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.