SRB_REL3.1_G4TSKINONLY_LONGWAVE_3HRLYMONTHLY - Special Edition GEWEX Longwave Monthly Averaged 3-Hourly (Diurnal) Data Set README File 1.0 Introduction This README file provides information on the SRB_REL3.1_G4TSKINONLY_LONGWAVE_3HRLYMONTHLY data set. The data set contains monthly averaged 3-hour 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 (i.e., a global instantaneous gridded field every 3 hours). The 3-hourly values are used to compute monthly averages separately for each of the 8 UT hours (00, 03, 06, 09, 12, 15, 18, and 21 UT). The current version of the datasets 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 -0.24 W/m**2 (0.07%, model fluxes lower), and the root mean square difference is 14.1 W/m**2 (4.5%). 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, mean bias for the present results is within the uncertainty for BSRN measurements. Errors for individual 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 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 files contains monthly average/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_3hrlymonthly_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 3hrlymonthly 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 averaged/3-hourly values of the six radiative parameters on the nested grid. Each file has 6 records, containing one global field for every time period in each record. The parameters are: 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_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 (srb_rel31_g4tskinonly_longwave_3hrlymonthly.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_3hrlymonthly read_srb_rel3.1_g4tskinonly_lw_3hrlymonthly.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_3hrlymonthly 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 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) at hour 06. 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_3hrlymonthly 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_3hrlymonthly_199807.binary Variable clr_toa_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 248.089 248.686 248.686 249.523 249.523 lat band # 46 251.486 251.889 252.269 252.751 252.972 lat band # 47 255.060 255.314 255.546 255.801 255.316 lat band # 48 257.365 257.515 257.661 257.572 256.970 lat band # 49 258.695 258.670 258.804 258.756 258.405 lat band # 50 260.201 260.134 260.324 260.533 260.418 lat band # 51 262.267 262.343 262.644 263.023 263.010 file clr_toa_up_G4TskinOnly_3hrlymonthly_199807.ascii has been written Variable clr_sfc_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 353.611 354.450 354.450 354.439 354.439 lat band # 46 359.351 359.850 359.871 359.671 359.545 lat band # 47 364.130 364.562 364.638 364.498 363.829 lat band # 48 366.644 366.835 366.950 366.964 366.256 lat band # 49 367.621 367.546 367.732 367.945 367.494 lat band # 50 368.974 368.981 369.431 369.947 369.684 lat band # 51 371.231 371.627 372.471 373.371 373.228 file clr_sfc_up_G4TskinOnly_3hrlymonthly_199807.ascii has been written Variable clr_sfc_down_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 257.694 257.685 257.685 256.928 256.928 lat band # 46 261.246 261.231 260.991 260.529 260.254 lat band # 47 263.959 263.985 263.888 263.697 263.766 lat band # 48 266.071 266.106 266.196 266.275 266.606 lat band # 49 268.092 268.050 268.282 268.362 268.582 lat band # 50 270.428 270.394 270.406 270.365 270.485 lat band # 51 272.805 272.734 272.631 272.771 273.306 file clr_sfc_down_G4TskinOnly_3hrlymonthly_199807.ascii has been written Variable toa_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 210.955 213.196 213.196 220.001 220.001 lat band # 46 217.362 216.970 221.621 222.445 222.114 lat band # 47 221.481 227.886 228.216 225.049 226.293 lat band # 48 234.068 236.259 233.386 229.749 229.585 lat band # 49 240.413 240.577 236.761 232.532 233.272 lat band # 50 239.250 238.401 238.669 237.839 235.196 lat band # 51 238.858 238.340 238.553 235.482 239.772 file toa_up_G4TskinOnly_3hrlymonthly_199807.ascii has been written Variable sfc_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 354.371 355.240 355.240 355.227 355.227 lat band # 46 360.164 360.670 360.732 360.438 360.348 lat band # 47 364.968 365.317 365.403 365.320 364.691 lat band # 48 367.367 367.525 367.742 367.784 367.048 lat band # 49 368.286 368.226 368.394 368.784 368.281 lat band # 50 369.740 369.688 370.135 370.635 370.377 lat band # 51 372.077 372.424 373.219 374.136 374.026 file sfc_up_G4TskinOnly_3hrlymonthly_199807.ascii has been written Variable sfc_down_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 308.305 310.257 310.257 309.304 309.304 lat band # 46 315.395 315.954 318.403 311.473 313.510 lat band # 47 319.866 314.277 314.863 318.492 321.141 lat band # 48 314.295 312.204 319.037 321.066 319.666 lat band # 49 312.687 313.475 312.585 324.485 321.272 lat band # 50 321.769 317.771 317.661 316.441 316.861 lat band # 51 329.701 326.305 322.959 324.091 327.041 file sfc_down_G4TskinOnly_3hrlymonthly_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.