GEWEX Shortwave 3-hourly/monthly README file 1.0 Introduction This README file provides information on the SRB_REL2_SW_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 15 shortwave (SW) surface radiative parameters derived with the Shortwave 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 The data is generated using the Pinker/Laszlo shortwave algorithm (R.T. Pinker and I. Laszlo, 1992: Modeling Surface Solar Irradiance for Satellite Applications on a Global Scale, J. Appl. Met., 31, 194-211). 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 3-hourly values were used to compute monthly averages separately for each of the 8 UT hours. The current version of the data is identified as Release 2. There are a total of 15 parameters in these files as follows: 1. TOA Downward Flux 2. All Sky TOA Upward Flux 3. All Sky Surface Downward Flux 4. All Sky Surface Downward Diffuse Flux 5. All Sky Surface Upward Flux 6. Clear Sky TOA Upward Flux 7. Clear Sky Surface Downward Flux 8. Clear Sky Surface Upward Flux 9. All Sky Global Photosynthetically Active Radiative Flux (PAR) 10. All Sky Diffuse PAR 11. Aerosol Optical Depth* 12. Cloud Optical Depth* 13. Cloud Fraction 14. Cosine Solar Zenith Angle from Satellite 15. Cosine Solar Zenith Angle from Astronomy (center of 3 hour period) The last two are very similar; they differ only slightly because the satellite retrieval time is not always centered on the 3-hourly ISCCP time stamp (0, 3, 6, 9, 12, 15, 18 and 21 UT). *Note that in the Pinker-Laszlo algorithm, aerosol and cloud optical depths are used as tuning parameters. That is, any difference between ISCCP clear-sky composite radiance and instantaneous radiance, is ascribed to aerosol in the clear fraction of the gridbox, and to cloud optical depth in the cloudy fraction. The resulting aerosol field in particular is not representative of a realistic aerosol field. The cloud optical depth returned by the algorithm agrees fairly well with the ISCCP-derived optical depth, except over ice. 2.1 Data Quality An assessment of the quality of these diurnal fluxes was accomplished by comparisons with corresponding ground-measured fluxes over a period of four years (1992-1995) 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 -0.6 W/m**2, and the root mean square difference is 34.3 W/m**2. Uncertainties associated with operational BSRN measurements during this period are believed to be about +/- 5-15 W/m**2 (Ellsworth Dutton, NOAA, BSRN Manager). Thus, mean bias for the present results is within the uncertainty for BSRN measurements. 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 shortwave radiation is therefore higher in the gap, whereas downward longwave radiation is lower creating an appearance of a flux discontinuity. The discontinuity approaches 60 W/m**2 raising the uncertainty of the fluxes in this region. For 3-hourly fluxes a discontinuity may appear in the Indian Ocean depending upon the prevalent meteorological conditions. Significant areas within this region may also be missing depending upon the hour due to the lack of geosynchronous coverage. 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 a 4-D data assimilation product provided by the Data Assimilation Office at NASA GSFC and were produced with the Goddard Earth Observing System model version 1 (GEOS-1). Column ozone for the July 1983 to November 1994 period were taken from the Total Ozone Mapping Spectrometer (TOMS) data from flights aboard Nimbus-7 and Meteor-3. Column ozone for December 1994 to October 1995 were taken from TIROS Operational Vertical Sounder (TOVS) data. Surface albedos are derived with a parameterization using monthly climatological clear-sky TOA albedos which are based on ERBE measurements during the 1985-1989 period. 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 3-hourly/monthly average 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 contain binary data and are named according to the following convention: srb_rel2_shortwave_3hrlymonthly_yyyymm.binary, where srb Project name, Surface Radiation Budget rel2 Release number for these data (Release 2) shortwave Name of the algorithm, GEWEX Shortwave 3hrlymonthly 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/monthly averages of the following fifteen parameters on the nested grid. Name: TOA Downward SW Flux Units: Watts per square meter Type: Real Range: 0 to 1400 Fill Values: -1000.0 Scale Factor: None Name: All Sky TOA Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 1100 Fill Values: -1000.0 Scale Factor: None Name: All Sky Surface Downward SW Flux Units: Watts per square meter Type: Real Range: 0 to 1200 Fill Values: -1000.0 Scale Factor: None Name: All Sky Surface Downward Diffuse SW Flux Units: Watts per square meter Type: Real Range: 0 to 900 Fill Values: -1000.0 Scale Factor: None Name: All Sky Surface Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 700 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky TOA Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 700 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky Surface Downward SW Flux Units: Watts per square meter Type: Real Range: 0 to 1200 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky Surface Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 700 Fill Values: -1000.0 Scale Factor: None Name: All Sky Global Photosynthetically Active Radiation Flux Units: Watts per square meter Type: Real Range: 0 to 550 Fill Values: -1000.0 Scale Factor: None Name: All Sky Diffuse Photosynthetically Active Radiation Flux Units: Watts per square meter Type: Real Range: 0 to 450 Fill Values: -1000.0 Scale Factor: None Name: Aerosol Optical Depth Units: Dimensionless Type: Real Range: 0 to 1.5 Fill Values: -1000.0 Scale Factor: None Name: Cloud Optical Depth Units: Dimensionless Type: Real Range: 0 to 500 Fill Values: -1000.0 Scale Factor: None Name: Cloud Fraction Units: Dimensionless Type: Real Range: 0 to 1 Fill Values: -1000.0 Scale Factor: None Name: Cosine Solar Zenith Angle From Satellite Units: Dimensionless Type: Real Range: 0 to 1 Fill Values: -1000.0 Scale Factor: None Name: Cosine Solar Zenith Angle From Astronomy (center of 3 hour period) Units: Dimensionless Type: Real Range: 0 to 1 Fill Values: -1000.0 Scale Factor: None 5.0 Description of Sample Read Software Sample read software written in Fortran-90, read_shortwave_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 (shortwave_3hrlymonthly.nml). The input files are binary on the nested (44016 box) grid. The software reads one or more of the 15 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=12 ascii=.true. binary=.false. path_in='**** input file path here ****' path_out='**** output file path here ****' little_endian=.false. gmt=.true. toa_down=.true. toa_up=.true. sfc_down=.true. sfc_diff=.true. sfc_up=.true. clr_toa_up=.true. clr_sfc_down=.true. clr_sfc_up=.true. par=.true. diff_par=.true. aer_opt_dep=.true. cld_opt_dep=.true. cld_frac=.true. cos_sza=.true. ave_cos_sza=.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. 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_shortwave_3hrly read_shortwave_3hrly.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_shortwave_3hrlymonthly 7.0 Sample Output When the code runs, the following information appears on the screen: The fifteen tables of numbers below show the values of the three 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. ***************************************************************** * * * * * Data Set srb_rel2_shortwave_3hrlymonthly Read Software * * * * Version: 1.0 * * * * Date: February 12, 2003 * * * * 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_shortwave_3hrlymonthly_199212.binary input file is opened cell_longitudes.dat is opened Variable toa_down_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 1221.183 1215.499 1215.499 1208.797 1208.797 lat band # 46 1228.099 1225.207 1222.055 1218.645 1214.977 lat band # 47 1235.966 1233.025 1229.819 1226.351 1222.620 lat band # 48 1243.456 1240.467 1237.209 1233.683 1229.892 lat band # 49 1250.568 1247.531 1244.222 1240.640 1236.789 lat band # 50 1257.299 1254.215 1250.855 1247.219 1243.309 lat band # 51 1263.646 1260.518 1257.108 1253.418 1249.450 file toa_down_3hrlymonthly_199212.ascii has been written Variable toa_up_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 457.340 441.822 441.822 434.497 434.497 lat band # 46 469.387 450.950 474.177 445.435 427.913 lat band # 47 454.795 460.311 467.227 457.514 417.748 lat band # 48 425.134 402.300 426.234 400.384 367.663 lat band # 49 393.624 404.655 396.211 368.464 340.574 lat band # 50 354.484 327.248 338.372 350.855 373.637 lat band # 51 371.759 369.365 360.335 355.617 334.724 file toa_up_3hrlymonthly_199212.ascii has been written Variable sfc_down_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 536.829 550.741 550.741 553.466 553.466 lat band # 46 531.470 548.711 513.557 547.219 564.283 lat band # 47 549.523 540.993 531.556 538.822 583.830 lat band # 48 589.528 618.039 587.268 611.141 649.846 lat band # 49 637.148 617.486 623.883 657.266 685.453 lat band # 50 689.708 720.225 701.615 683.328 650.449 lat band # 51 672.614 674.807 684.623 684.639 705.936 file sfc_down_3hrlymonthly_199212.ascii has been written Variable sfc_diff_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 464.757 469.516 469.516 465.059 465.059 lat band # 46 438.866 442.674 447.044 433.848 483.242 lat band # 47 437.152 441.994 467.484 454.593 475.521 lat band # 48 488.861 521.150 513.232 541.945 529.990 lat band # 49 481.449 512.151 529.792 523.929 553.967 lat band # 50 546.875 593.662 600.348 544.754 515.830 lat band # 51 585.058 555.557 559.629 548.846 556.344 file sfc_diff_3hrlymonthly_199212.ascii has been written Variable sfc_up_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 29.935 31.288 31.288 31.651 31.651 lat band # 46 30.071 29.577 28.758 31.043 33.356 lat band # 47 29.408 28.136 31.169 31.973 33.572 lat band # 48 32.756 35.654 34.658 35.800 37.453 lat band # 49 35.897 35.459 36.069 37.502 38.672 lat band # 50 40.270 42.246 40.977 39.620 37.058 lat band # 51 39.849 39.538 40.114 39.015 40.111 file sfc_up_3hrlymonthly_199212.ascii has been written Variable clr_toa_up_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 91.842 99.371 99.371 96.652 96.652 lat band # 46 99.588 93.483 93.581 103.765 113.108 lat band # 47 91.406 84.715 108.036 113.427 104.951 lat band # 48 96.335 106.913 109.506 107.676 107.502 lat band # 49 105.517 106.597 105.101 103.458 102.089 lat band # 50 111.617 109.783 108.809 109.773 104.157 lat band # 51 113.616 110.696 110.926 104.315 106.957 file clr_toa_up_3hrlymonthly_199212.ascii has been written Variable clr_sfc_down_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 983.460 974.362 974.362 967.814 967.814 lat band # 46 989.499 981.838 978.434 976.322 969.143 lat band # 47 992.784 986.177 985.770 980.747 976.226 lat band # 48 996.614 991.181 989.695 985.466 980.903 lat band # 49 1000.127 995.279 993.930 992.133 988.376 lat band # 50 1004.118 1003.925 999.262 993.368 991.985 lat band # 51 1011.931 1007.975 1002.812 1001.819 993.685 file clr_sfc_down_3hrlymonthly_199212.ascii has been written Variable clr_sfc_up_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 32.568 39.604 39.604 37.482 37.482 lat band # 46 42.585 33.121 33.547 45.956 54.639 lat band # 47 32.663 23.019 51.128 56.390 47.079 lat band # 48 37.961 48.118 52.486 50.211 49.976 lat band # 49 47.436 47.445 47.302 46.765 45.550 lat band # 50 53.727 53.400 51.767 51.571 46.801 lat band # 51 57.570 53.753 53.071 47.400 47.402 file clr_sfc_up_3hrlymonthly_199212.ascii has been written Variable par_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 264.066 269.408 269.408 271.258 271.258 lat band # 46 260.972 267.449 254.799 268.613 277.190 lat band # 47 268.336 265.522 263.917 266.337 285.815 lat band # 48 288.517 301.465 289.141 301.010 315.998 lat band # 49 308.887 302.541 306.920 319.768 333.249 lat band # 50 334.357 348.310 339.829 331.771 316.455 lat band # 51 328.746 327.154 331.787 332.418 340.343 file par_3hrlymonthly_199212.ascii has been written Variable diff_par_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 231.924 233.821 233.821 232.984 232.984 lat band # 46 220.887 221.828 225.554 219.343 241.179 lat band # 47 218.930 222.013 234.893 229.612 238.198 lat band # 48 244.177 258.659 255.466 269.650 263.095 lat band # 49 240.986 256.281 265.136 260.306 274.290 lat band # 50 271.382 291.232 293.430 270.081 255.955 lat band # 51 288.813 273.865 275.917 271.796 273.772 file diff_par_3hrlymonthly_199212.ascii has been written Variable aer_opt_dep_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 0.129 0.151 0.151 0.141 0.141 lat band # 46 0.115 0.143 0.142 0.135 0.162 lat band # 47 0.122 0.146 0.131 0.143 0.138 lat band # 48 0.128 0.154 0.136 0.140 0.142 lat band # 49 0.142 0.160 0.141 0.124 0.117 lat band # 50 0.153 0.128 0.137 0.154 0.133 lat band # 51 0.134 0.141 0.153 0.127 0.166 file aer_opt_dep_3hrlymonthly_199212.ascii has been written Variable cld_opt_dep_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 19.138 32.891 32.891 29.387 29.387 lat band # 46 44.195 40.452 28.993 22.103 17.667 lat band # 47 32.362 28.955 25.665 27.642 23.422 lat band # 48 23.747 19.704 23.501 12.426 18.692 lat band # 49 20.786 17.055 14.699 18.143 6.978 lat band # 50 7.964 5.761 8.961 8.641 12.394 lat band # 51 8.938 19.082 22.639 19.721 16.609 file cld_opt_dep_3hrlymonthly_199212.ascii has been written Variable cld_frac_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 0.906 0.885 0.885 0.871 0.871 lat band # 46 0.875 0.854 0.898 0.844 0.885 lat band # 47 0.859 0.869 0.914 0.872 0.852 lat band # 48 0.875 0.875 0.906 0.906 0.844 lat band # 49 0.805 0.865 0.875 0.844 0.850 lat band # 50 0.828 0.856 0.883 0.836 0.844 lat band # 51 0.896 0.859 0.850 0.844 0.825 file cld_frac_3hrlymonthly_199212.ascii has been written Variable cos_sza_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 0.880 0.877 0.877 0.874 0.874 lat band # 46 0.883 0.879 0.879 0.878 0.875 lat band # 47 0.889 0.888 0.884 0.881 0.879 lat band # 48 0.895 0.893 0.889 0.889 0.887 lat band # 49 0.900 0.898 0.897 0.895 0.891 lat band # 50 0.905 0.901 0.900 0.898 0.897 lat band # 51 0.909 0.908 0.905 0.902 0.900 file cos_sza_3hrlymonthly_199212.ascii has been written Variable ave_cos_sza_Hour = 3 lon # = 100 101 102 103 104 lat band # 45 0.870 0.866 0.866 0.861 0.861 lat band # 46 0.875 0.873 0.870 0.868 0.865 lat band # 47 0.880 0.878 0.876 0.873 0.871 lat band # 48 0.886 0.884 0.881 0.879 0.876 lat band # 49 0.891 0.889 0.886 0.884 0.881 lat band # 50 0.896 0.893 0.891 0.888 0.886 lat band # 51 0.900 0.898 0.895 0.893 0.890 file ave_cos_sza_3hrlymonthly_199212.ascii has been written 8.0 Additional Derivable Parameters Additional parameters can be computed if needed, e.g.: Cloud Radiative Forcing = All Sky Surface Downward Flux - Clear Sky Surface Downward Flux Surface Albedo = All Sky Surface Upward Flux / All Sky Surface Downward Flux