SRB_REL3.1_G4TSKINONLY_LONGWAVE_MONTHLY - Special Edition GEWEX Longwave Monthly-Average Data Set README File 1.0 Introduction This README file provides information on the SRB_REL3.1_G4TSKINONLY_LONGWAVE_MONTHLY data set. The data set contains monthly average global fields of six longwave (LW) surface and Top of Atmosphere (TOA) radiative parameters 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 six parameters in these files as follows: 1. TOA Upward Clear-Sky Flux/Clear-sky Outgoing Longwave Radiation (OLR) (clr_toa_up) 2. Surface Clear-sky Upward Longwave Flux (clr_sfc_up) 3. Surface Clear-sky Downward Longwave Flux (clr_sfc_down) 4. TOA All-Sky Upward Longwave Flux/OLR (toa_up) 5. Surface All-Sky Upward Longwave Flux (sfc_up) 6. Surface All-Sky Downward Longwave Flux (sfc_down) These parameters are derived originally on a 3-hourly temporal resolution. The 3-hourly values are averaged into monthly averages given in these files. The current version of the data sets is identified as 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. Additionally, 3-hourly values of NaN's were detected and were traced to en error in the temperature profiles. The frequency of this occurrence was far more rare and was found to be mostly clustered for three months in 1987 and July 1990. After correcting the temperature profiles, the grid boxes were recomputed and replaced in the 3-hourly files using the same "non optimized" version of the code. 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 0.03 W/m**2 (0.01%, model fluxes higher), and the root mean square difference is 11.1 W/m**2 (3.5%). Uncertainties associated with operational BSRN measurements during this period are believed to be about +/- 3-5 W/m**2 (1-1.5%, Ellsworth Dutton, NOAA, BSRN Manager). Thus, the mean bias for the present results is within the uncertainty for BSRN measurements. Errors for individual monthly 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 monthly averaged 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_monthly_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 monthly 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 monthly averages of the six parameters on the nested grid. Each file has 6 records, containing one global field in each record. 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_longwave_monthly.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_monthly.nml). The input files are read as direct-access binary on the nested (44016 box) grid. The software reads one or more of the 6 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. 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_monthly read_srb_rel3.1_g4tskinonly_lw_monthly.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_monthly 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=infile,status='old',form='unformatted',access='direct',recl=4*nreg) should be modified to: open (10,file=infile,status='old',form='unformatted',access='direct',recl=nreg) 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 six 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). Values for only a small lat-lon box are printed to the screen. When the is code run, the following information appears on the screen: ***************************************************************** * * * * * Data Set read_srb_rel31_g4tskinonly_lw_monthly 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: support-asdc@earthdata.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * ***************************************************************** srb_rel3.1_G4TskinOnly_longwave_monthly_199807.binary input file is opened Variable clr_toa_up_ lon # = 100 101 102 103 104 lat band # 45 247.482 247.822 247.822 248.168 248.168 lat band # 46 250.371 250.571 250.859 251.061 251.142 lat band # 47 253.289 253.560 253.779 253.885 253.572 lat band # 48 255.500 255.635 255.750 255.709 255.309 lat band # 49 257.086 257.067 257.087 257.047 256.838 lat band # 50 258.737 258.703 258.782 258.931 258.911 lat band # 51 260.899 261.003 261.276 261.608 261.584 file clr_toa_up_G4TskinOnly_monthly_199807.ascii has been written Variable clr_sfc_up_ lon # = 100 101 102 103 104 lat band # 45 353.570 354.403 354.403 354.400 354.400 lat band # 46 359.306 359.801 359.822 359.627 359.504 lat band # 47 364.089 364.515 364.590 364.450 363.776 lat band # 48 366.611 366.793 366.902 366.910 366.192 lat band # 49 367.587 367.504 367.681 367.888 367.427 lat band # 50 368.934 368.934 369.377 369.888 369.615 lat band # 51 371.183 371.575 372.418 373.311 373.154 file clr_sfc_up_G4TskinOnly_monthly_199807.ascii has been written Variable clr_sfc_down_ lon # = 100 101 102 103 104 lat band # 45 256.272 256.420 256.420 256.325 256.325 lat band # 46 259.975 259.959 259.879 259.814 259.753 lat band # 47 263.054 262.988 262.930 262.950 262.855 lat band # 48 265.650 265.520 265.427 265.396 265.390 lat band # 49 267.785 267.559 267.513 267.483 267.356 lat band # 50 269.861 269.687 269.602 269.501 269.243 lat band # 51 271.878 271.832 271.834 271.827 271.767 file clr_sfc_down_G4TskinOnly_monthly_199807.ascii has been written Variable toa_up_ lon # = 100 101 102 103 104 lat band # 45 214.595 213.043 213.043 214.020 214.020 lat band # 46 216.497 214.134 217.405 218.734 217.522 lat band # 47 221.866 223.363 222.697 223.786 224.036 lat band # 48 229.121 229.827 228.331 227.969 227.055 lat band # 49 233.388 233.037 232.907 230.990 229.845 lat band # 50 236.483 235.770 235.480 235.155 233.861 lat band # 51 239.545 239.277 239.246 239.089 239.387 file toa_up_G4TskinOnly_monthly_199807.ascii has been written Variable sfc_up_ lon # = 100 101 102 103 104 lat band # 45 354.387 355.224 355.224 355.209 355.209 lat band # 46 360.128 360.639 360.648 360.421 360.304 lat band # 47 364.889 365.324 365.414 365.249 364.565 lat band # 48 367.389 367.542 367.671 367.682 366.959 lat band # 49 368.344 368.230 368.419 368.676 368.257 lat band # 50 369.734 369.702 370.130 370.634 370.404 lat band # 51 372.026 372.377 373.202 374.068 373.891 file sfc_up_G4TskinOnly_monthly_199807.ascii has been written Variable sfc_down_ lon # = 100 101 102 103 104 lat band # 45 310.635 310.997 310.997 310.107 310.107 lat band # 46 314.788 315.798 314.878 312.630 312.934 lat band # 47 316.442 317.058 318.011 316.258 315.485 lat band # 48 317.802 315.624 316.873 317.039 316.750 lat band # 49 318.585 316.232 317.066 320.335 323.058 lat band # 50 323.694 321.333 320.213 319.632 322.148 lat band # 51 328.658 325.825 324.609 322.738 321.350 file sfc_down_G4TskinOnly_monthly_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.