SRB_REL3.1_G4TSKINONLY_LONGWAVE_3HRLY - Special Edition GEWEX Longwave 3-Hourly Data Set README File 1.0 Introduction This README file provides information on the SRB_REL3.1_G4TSKINONLY_LONGWAVE_3HRLY data set. The data set contains 3-hourly global fields of six longwave (LW) surface and Top of Atmosphere (TOA) radiative parameters, in addition to a day/night flag, derived with the Longwave algorithm of the NASA World Climate Research Programme/Global Energy and Water-Cycle Experiment (WCRP/GEWEX) Surface Radiation Budget (SRB) Project. This is a special 10-year data set that uses only the GEOS-4 value of surface skin temperature in the flux calculations, not the ISCCP/GEOS-4 surface skin temperature blend. If users have questions, please contact the Langley Atmospheric Science Data Center (ASDC) User and Data Services Office at: Atmospheric Science Data Center User and Data Services Office Mail Stop 157D NASA Langley Research Center Hampton, Virginia 23681-2199 U.S.A. E-mail: support-asdc@earthdata.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 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 References 2.0 Data Set Description There are a total of seven parameters in these files as follows: 1. Day/Night flag (daynite; 1=Day, 0=Night) 2. TOA Upward Clear-Sky Flux/Clear-sky Outgoing Longwave Radiation (OLR) (clr_toa_up) 3. Surface Clear-sky Upward Longwave Flux (clr_sfc_up) 4. Surface Clear-sky Downward Longwave Flux (clr_sfc_down) 5. TOA All-Sky Upward Longwave Flux/OLR (toa_up) 6. Surface All-Sky Upward Longwave Flux (sfc_up) 7. Surface All-Sky Downward Longwave Flux (sfc_down) These parameters were derived originally on a 3-hourly temporal resolution (i.e., a global instantaneous gridded field every 3 hours), at UT hours 00, 03, 06, 09, 12, 15, 18, and 21 for every day of the month. The current version of the data set is Release 3.1, with this special version having a name modifier of G4TskinOnly. The GEWEX LW algorithm uses the Fu et al. (1997) thermal infrared radiative transfer code requiring atmospheric profile information, cloud, and surface properties. The sources for these inputs are briefly described below. A detailed description of the algorithm is currently being prepared for publication. Please contact the Dr. Paul W. Stackhouse Jr. at the address below for further details. Version History: Release 2.1: 12 year data set (July 1983-October 1995), on nested grid (described in Section 2.3), using GEOS-1 meteorological data. Release 2.5: 22 year data set (July 1983-June 2005). Using GEOS-4 meteorological inputs for the data set in place of GEOS-1. Release 3.0: 24.5 year data set (July 1983-December 2007). This version includes improved cloud properties in areas in missing and sun glint regions where ISCCP cloud retrievals aren't performed. Additionally, the IR radiative parameterization of ice clouds has been updated (Fu et al. 1998). The water vapor continuum has been updated (Kratz and Rose, 1999). An error in the ozone profile assignment is corrected. The surface vegetation type maps have been updated. This affects the surface emissivity values (Rutan et al. 2009). CO2 concentration value now varies month to month, based on monthly trend values from ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_gl.txt Release 3.1: Corrections to nonphysical fluxes have been made to Rel. 3.0. Negative TOA fluxes in the 3-hourly data files were found to occur about 7 grid box times per month (out of 44016 grid boxes x 248 hours per month), with an additional 5 to 10 values per month identified as being unphysically low. The problem was found to be an numerical instability occurring due to an optimization switch in the Fortran compiler. The downwelling fluxes were also affected. So, the nonphysical values were replaced with a recomputation of those grid boxes using the same code but built without an optimization. The daily, monthly and 3-hourly monthly files were reprocessed using the improved 3-hourly files. Differences in the monthly averages proved to be small and mostly < 2 W m^-2 on a grid box level and < 0.01 W m^-2 on a global mean. Differences on the grid box level in the 3-hourly monthly and daily averages were mostly < 10 W m^-2. G4TSKINONLY: 10 year data set (January 1998-December 2007). In the regular release 3.1 version, the surface skin temperature used in flux calculations is a blend of GEOS-4 and ISCCP surface skin temperatures based upon cloud fraction. In this version, only GEOS-4 surface skin temperatures are used. This is the only difference from GEWEX LW release 3.1. 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 from January 1992 to December 2007 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 1.04W/m**2 (0.3%, model fluxes higher), and the root mean square difference is 29.9 W/m**2 (9.5%). Uncertainties associated with operational BSRN measurements during this period are believed to be about +/- 5 W/m**2 (1.5%, Ellsworth Dutton, NOAA, BSRN Manager). Thus, mean bias for the present results is within the uncertainty of BSRN measurements. Errors for individual 3-hourly values may be different from the above values because those are subject to bias and random errors due to local meteorological conditions. 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 (Rossow and Schiffer, 1999) DX data product. The cloud pixels were separated into categories of high, middle and low where middle and low clouds could be composed of ice or water, while high clouds were composed of ice only. Cloud fractions and cloud optical depths were determined within these categories. Cloud particle sizes were assumed and cloud physical thicknesses were also assigned based upon information from literature. Random overlap is used between the high, middle and low layers to better approximate undercast conditions. 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) Column ozone values for January 1998 to December 2004 were obtained primarily from the Total Ozone Mapping Spectrometer (TOMS) archive as EP-TOMS. 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. Column ozone data continued to be available beyond December 2004 from OMI instrument aboard Aura satellite but TOVS data, which is essential for filling the gaps in OMI data, developed some unexplained gaps of its own and became unusable. Beginning in January 2005, GEWEX/SRB started using a daily analysis ozone product from NOAA Climate Predictions Center (CPC), known as the Stratospheric Monitoring-group Ozone Blended Analysis (SMOBA). Surface emissivities were taken from a map developed at NASA LaRC (Wilber et al. 1999). 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 Science Data Center User and Data Services Office Mail Stop 157D NASA Langley Research Center Hampton, VA 23681-2199 U.S.A. E-mail: support-asdc@earthdata.nasa.gov 3.0 Format and Packaging Each data file contains 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 contain binary data and are named according to the following convention: srb_rel3.1_G4TskinOnly_longwave_3hrly_yyyymm.binary, where srb Project name, Surface Radiation Budget rel3.1 Release number for these data (Release 3.1) G4TskinOnly Indicates this special edition longwave Name of the algorithm, GEWEX Longwave 3hrly Time resolution of the data file yyyy 4-digit year mm 2-digit month binary file format 4.0 Science Parameters Information The files contain global fields of 3-hourly values of the day/night flag and the six radiative parameters on the nested grid. Each file has 7 records, containing one global field for every time period in each record. The parameters are: Name: Day/Night flag (Day=1, Night=0) Units: none Type: real Range: 0.0 or 1.0 Fill Values: n/a Scale Factor: None Name: Top-of-Atmosphere Clear-sky Upward LW Flux Units: Watts per square meter Type: Real Range: 50 to 600 Fill Values: -999.0 Scale Factor: None Name: Surface Clear-sky Upward LW Flux Units: Watts per square meter Type: Real Range: 50 to 800 Fill Values: -999.0 Scale Factor: None Name: Surface Clear-sky Downward LW Flux Units: Watts per square meter Type: Real Range: 50 to 600 Fill Values: -999.0 Scale Factor: None Name: Top-of-Atmosphere All-sky Upward LW Flux Units: Watts per square meter Type: Real Range: 50 to 600 Fill Values: -999.0 Scale Factor: None Name: Surface All-sky Upward LW Flux Units: Watts per square meter Type: Real Range: 50 to 800 Fill Values: -999.0 Scale Factor: None Name: Surface All-sky Downward LW Flux Units: Watts per square meter Type: Real Range: 50 to 600 Fill Values: -999.0 Scale Factor: None 5.0 Sample Read Software Description Sample read software written in Fortran-90, read_srb_rel3.1_g4tskinonly_lw_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_rel31_g4tskinonly_longwave_3hrly.nml). The input files are read as direct-access binary on the nested (44016 box) grid. The software reads one or more of the 7 parameter fields, regrids them to an equal-angle 1 deg x 1 deg grid, and writes the 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 1998 data file and write all parameters to an ascii format output file is presented below: &time_vars yr=1998 mon=7 ascii=.true. binary=.false. path_in='**** input file path here****' path_out='**** output file path here****' little_endian=.false. daynite=.true. clr_toa_up=.true. clr_sfc_up=.true. clr_sfc_down=.true. toa_up=.true. sfc_up=.true. sfc_down=.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 machines used to create the data set, such as Linux and Macs with the Intel chip. 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 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_longwave_3hrly read_srb_rel3.1_g4tskinonly_lw_3hrly.f90 The providers used a gfortran 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_longwave_3hrly 6.1 Read Software Incompatibilities With some Fortran compilers the RECL keyword in the OPEN statement assumes record lengths are specified in 4 byte increments. If that is the case, then the following statement in the read program: open(10,file=file_in,status='old',access='direct', & form='unformatted', recl=44016*4) should be modified to: open(10,file=file_in,status='old',access='direct', & form='unformatted', recl=44016) The same should be done with the output binary file: open (15,file=outfile, form='unformatted', access='direct', & recl=nlon*nlat*4, status='replace') should be modified to: open (15,file=outfile, form='unformatted', access='direct', & recl=nlon*nlat, status='replace') 7.0 Sample Output The seven 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. When the software is run, the following information appears on the screen: ***************************************************************** * * * * * Data Set srb_rel3.1_G4TskinOnly_longwave_3hrly Read Software * * * * Version: 1.0 * * * * Contact: Atmospheric Science Data Center * * User and Data Services Office * * Mail Stop 157D * * NASA Langley Research Center * * Hampton, Virginia 23681-2199 * * U.S.A. * * * * E-mail: support-asdc@earthdata.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * ***************************************************************** srb_rel3.1_G4TskinOnly_longwave_3hrly_199807.binary input file is opened Variable daynite_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 1.000 1.000 1.000 1.000 1.000 lat band # 46 1.000 1.000 1.000 1.000 1.000 lat band # 47 1.000 1.000 1.000 1.000 1.000 lat band # 48 1.000 1.000 1.000 1.000 1.000 lat band # 49 1.000 1.000 1.000 1.000 1.000 lat band # 50 1.000 1.000 1.000 1.000 1.000 lat band # 51 1.000 1.000 1.000 1.000 1.000 file daynite_G4TskinOnly_3hrly_199807.ascii has been written Variable clr_toa_up_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 248.092 248.005 248.005 247.658 247.658 lat band # 46 252.554 251.961 251.480 251.118 250.364 lat band # 47 256.084 255.032 254.338 253.397 252.385 lat band # 48 257.654 256.291 254.962 253.916 253.155 lat band # 49 257.441 255.851 254.764 254.353 254.148 lat band # 50 257.097 256.095 255.731 255.872 256.325 lat band # 51 257.946 257.516 257.641 258.170 259.321 file clr_toa_up_G4TskinOnly_3hrly_199807.ascii has been written Variable clr_sfc_up_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 354.086 354.842 354.842 354.605 354.605 lat band # 46 360.014 360.426 360.376 360.103 359.512 lat band # 47 364.897 365.207 365.179 364.917 363.781 lat band # 48 367.415 367.454 367.462 367.319 366.187 lat band # 49 368.348 368.073 368.153 368.206 367.414 lat band # 50 369.594 369.390 369.755 370.167 369.634 lat band # 51 371.707 371.941 372.748 373.630 373.223 file clr_sfc_up_G4TskinOnly_3hrly_199807.ascii has been written Variable clr_sfc_down_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 278.376 278.234 278.234 278.312 278.312 lat band # 46 281.314 281.217 281.078 280.987 281.055 lat band # 47 283.948 284.370 284.862 285.055 283.791 lat band # 48 286.989 288.127 288.819 287.980 286.048 lat band # 49 289.833 290.336 290.123 288.221 286.543 lat band # 50 290.120 289.687 289.074 288.163 287.058 lat band # 51 287.583 287.574 287.955 289.160 288.409 file clr_sfc_down_G4TskinOnly_3hrly_199807.ascii has been written Variable toa_up_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 224.062 217.112 217.112 218.942 218.942 lat band # 46 233.962 222.362 228.234 239.981 243.923 lat band # 47 235.922 243.212 240.390 246.514 248.542 lat band # 48 243.811 243.219 243.593 244.607 245.051 lat band # 49 243.130 240.725 243.311 241.316 243.755 lat band # 50 245.126 240.315 241.139 245.715 248.377 lat band # 51 241.774 248.091 246.778 250.805 251.140 file toa_up_G4TskinOnly_3hrly_199807.ascii has been written Variable sfc_up_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 355.073 355.746 355.746 355.518 355.518 lat band # 46 360.945 361.423 361.294 361.011 360.067 lat band # 47 365.850 366.070 366.122 365.903 364.438 lat band # 48 368.371 368.367 368.392 368.252 367.094 lat band # 49 369.268 368.968 369.043 369.165 368.361 lat band # 50 370.550 370.297 370.710 371.103 370.233 lat band # 51 372.633 372.897 373.595 374.276 373.868 file sfc_up_G4TskinOnly_3hrly_199807.ascii has been written Variable sfc_down_ Hour = 06 Day = 14 lon # = 100 101 102 103 104 lat band # 45 346.746 340.891 340.891 341.509 341.509 lat band # 46 345.690 350.250 344.800 343.472 319.150 lat band # 47 350.059 343.978 350.188 352.900 328.757 lat band # 48 353.603 351.728 353.489 352.721 348.657 lat band # 49 354.205 352.963 352.088 355.051 352.192 lat band # 50 356.799 352.985 355.627 353.017 328.512 lat band # 51 351.864 353.687 346.470 333.600 333.139 file sfc_down_G4TskinOnly_3hrly_199807.ascii has been written 8.0 Additional Derivable Parameters The net LW flux at the top-of-atmosphere (TOA) is simply the TOA upward LW flux. The net LW flux at the surface can be defined as: Net LW Flux = Downward LW Flux - Upward LW Flux and is, therefore, generally a negative number. Net fluxes can be computed for the clear-sky and all-sky conditions. The estimates of clear-sky and all-sky fluxes also allow the estimation of the contribution by clouds to the all-sky fluxes. This is commonly referred to as the cloud radiative forcing (CRF) and is computed according to: CRF = Flux (all-sky) - Flux (clear-sky) Thus, the cloud radiative forcing on the downward longwave flux is generally positive because clouds act to increase the emission to the surface. In this way, the effect of the cloud emission on the fluxes can be estimated for each flux component. Lastly, providing TOA and surface fluxes allows one to derive the net radiative flux of the atmosphere. This is given by the relation Net Atmos. Flux = Net TOA Flux - Net Surface Flux For the LW, this flux is negative meaning that the atmosphere is cooling over the LW wavelengths. References: Bloom, Stephen, A. daSilva. D. Dee, M. Bosilovich, J-D. Chern, S. Pawson, S. Schubert, M. Sienkiewicz, I. Stajner, W-W. Tan, and M-L Wu, 2005: Documentation and Validation of the Goddard Earth Observing System (GEOS) Data Assimilation System, Version 4, NASA Technical Report,Report Number: NASA/TM-2005104606/ VOL26/VER4, Rept- 2005-01264-0/VOL26/VER4 Fu, Qiang, K. N. Liou, M. C. Cribb, T. P. Charlock, and A. Grossman, 1997: Multiple Scattering Parameterization in Thermal Infrared Radiative Transfer. J. Atmos. Sci. , Vol. 54, 2799-2812, doi: 10.1175/1520-0469(1997)054<2799:MSPITI>2.0.CO;2 Fu, Qiang, P. Yang, and W. B. Sun, 1998: An Accurate Parameterization of the Infrared Radiative Properties of Cirrus Clouds for Climate Models. J. Climate, Vol. 11, 2223-2237, doi: 10.1175/1520-0442(1998)011<2223:AAPOTI>2.0.CO;2 Kratz, David P. and Rose, Fred G., 1999: Accounting for Molecular Absorption Within the Spectral Range of the CERES Window Channel. J. Quant. Spectrosc. Radiat. Transfer, Vol. 61, 83-95. Rossow, William B. and R. A. Schiffer, 1999: Advances in Understanding Clouds from ISCCP. BAMS, Vol. 80, 2261-2287, doi: 10.1175/1520-0477(1999)080<2261:AIUCFI>2.0.CO;2. Rutan, D., F. Rose, M. Roman, N. Manalo-Smith, C. Schaaf, and T. Charlock (2009), Development and assessment of broadband surface albedo from Clouds and the Earth's Radiant Energy System Clouds and Radiation Swath data product, J. Geophys. Res., 114, D08125, doi:10.1029/2008JD010669. Wilber, Anne C., Kratz, D. P., Gupta, S. K., 1999: Surface Emissivity Maps for Use in Satellite Retrievals of Longwave Radiation, NASA Technical Report, Report Number: L-17861, NAS 1.60:209362, NASA/TP-1999-209362.