GEWEX Shortwave Daily README file 1.0 Introduction This README file provides information on the SRB_REL2_SW_DAILY data set. The data set contains daily average global fields of fifteen 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 2.1.2. Indian Ocean Gap Artifact 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 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. The 3-hourly values are averaged into daily values using a normalization correction to account for the discretization of the solar cycle. 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). All fluxes are in Watts per square meter. *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. It is important to note that the daily averages are representative of the local day, not the period from 0Z to 2359Z. 2.1 Data Quality An assessment of the quality of these daily average 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 1.7 W/m**2 (estimate - observation), and the random error to be about +/- 38.5 W/m**2. Uncertainties associated with the BSRN measurements during this time period are believed to be about +/- 5 - 15 W/m**2 (Ellsworth Dutton, NOAA, BSRN Manager) depending on environmental conditions. This includes a possible thermal offset which would result in a systematic bias of up to 3% (personal (personal communication, Rolf Philipona, World Radiation Center) depending on atmospheric humidity and cloudiness conditions. These flux estimates are within these uncertainties. 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, creating an appearance of a flux discontinuity. The discontinuity approaches 20 W/m**2 raising the uncertainty of the fluxes in this region. For Daily averaged fluxes, any discontinuity in instantaneous fluxes will be exacerbated by the temporal gaps of coverage in the Indian Ocean gap region. In this region, the shortwave local time daily average will be based upon fluxes from at most 2 daytime observations of the region while areas with geosynchronous coverage are sampled 3-5 times during the daylight hours. 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 (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. 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: p.w.stackhouse@larc.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 daily 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_daily_yyyymm.binary, where srb Project name, Surface Radiation Budget rel2 Release number for these data (Release 2) shortwave Name of the algorithm, GEWEX Shortwave daily 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 daily 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 575 Fill Values: -1000.0 Scale Factor: None Name: All Sky TOA Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 450 Fill Values: -1000.0 Scale Factor: None Name: All Sky Surface Downward SW Flux Units: Watts per square meter Type: Real Range: 0 to 475 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 325 Fill Values: -1000.0 Scale Factor: None Name: All Sky Surface Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 400 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky TOA Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 425 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky Surface Downward SW Flux Units: Watts per square meter Type: Real Range: 0 to 475 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky Surface Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 400 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 200 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 150 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 Sample Read Software Description Sample read software written in Fortran-90, read_shortwave_daily.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_daily.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=7 ascii=.true. binary=.false. path_in='**** input file path here ****' path_out='**** output file path here ****' little_endian=.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_daily read_shortwave_daily.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_daily 7.0 Sample Output 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. When the code runs, the following information appears on the screen: ***************************************************************** * * * * * Data Set srb_rel2_shortwave_daily 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_daily_199207.binary input file is opened Variable toa_down_Day = 14 lon # = 100 101 102 103 104 lat band # 45 122.016 122.016 122.016 122.016 122.016 lat band # 46 128.632 128.632 128.632 128.632 128.632 lat band # 47 135.265 135.265 135.265 135.265 135.265 lat band # 48 141.909 141.909 141.909 141.909 141.909 lat band # 49 148.560 148.560 148.560 148.560 148.560 lat band # 50 155.214 155.214 155.214 155.214 155.214 lat band # 51 161.865 161.865 161.865 161.865 161.865 file toa_down_daily_199207.ascii has been written Variable toa_up_Day = 14 lon # = 100 101 102 103 104 lat band # 45 65.195 63.429 63.429 58.725 58.725 lat band # 46 63.116 63.521 62.623 60.333 59.309 lat band # 47 62.145 55.931 62.271 61.220 64.363 lat band # 48 60.558 57.562 63.167 65.054 63.826 lat band # 49 63.205 71.052 64.040 60.431 63.013 lat band # 50 69.469 67.036 61.851 64.836 55.022 lat band # 51 64.807 54.841 49.873 57.111 50.850 file toa_up_daily_199207.ascii has been written Variable sfc_down_Day = 14 lon # = 100 101 102 103 104 lat band # 45 33.973 35.581 35.581 40.497 40.497 lat band # 46 41.843 41.478 42.537 45.000 46.079 lat band # 47 48.629 55.492 48.846 50.114 46.851 lat band # 48 56.116 59.578 53.875 52.010 53.206 lat band # 49 58.948 50.992 58.611 62.546 59.474 lat band # 50 58.029 60.796 66.443 63.205 73.707 lat band # 51 69.035 79.537 84.850 76.847 83.157 file sfc_down_daily_199207.ascii has been written Variable sfc_diff_Day = 14 lon # = 100 101 102 103 104 lat band # 45 33.973 35.579 35.579 40.490 40.490 lat band # 46 41.842 41.476 42.533 44.992 46.065 lat band # 47 48.583 55.321 48.821 50.086 46.834 lat band # 48 55.979 59.355 53.758 51.934 53.147 lat band # 49 58.798 50.962 58.455 62.231 56.974 lat band # 50 57.744 60.297 66.116 62.497 67.620 lat band # 51 68.709 70.931 75.266 74.136 77.802 file sfc_diff_daily_199207.ascii has been written Variable sfc_up_Day = 14 lon # = 100 101 102 103 104 lat band # 45 2.038 2.135 2.135 2.430 2.430 lat band # 46 2.511 2.489 2.552 2.700 2.764 lat band # 47 2.917 3.328 2.931 3.008 2.813 lat band # 48 3.368 3.575 3.246 3.126 3.197 lat band # 49 3.538 3.063 3.530 3.774 3.804 lat band # 50 3.521 3.713 4.007 3.838 4.791 lat band # 51 4.167 5.357 5.586 4.791 5.389 file sfc_up_daily_199207.ascii has been written Variable clr_toa_up_Day = 14 lon # = 100 101 102 103 104 lat band # 45 22.097 22.981 22.981 22.135 22.135 lat band # 46 22.707 22.644 23.158 23.641 21.825 lat band # 47 22.676 22.229 22.088 27.487 29.276 lat band # 48 24.509 23.697 33.019 29.817 29.613 lat band # 49 23.465 34.335 32.294 29.595 32.413 lat band # 50 32.569 32.507 31.619 29.179 32.916 lat band # 51 32.821 32.599 29.580 31.187 35.654 file clr_toa_up_daily_199207.ascii has been written Variable clr_sfc_down_Day = 14 lon # = 100 101 102 103 104 lat band # 45 79.579 79.746 79.746 80.227 80.227 lat band # 46 84.620 84.772 85.240 85.709 85.626 lat band # 47 89.828 90.089 90.448 91.256 91.735 lat band # 48 94.875 95.524 96.759 96.870 96.985 lat band # 49 100.049 101.573 101.657 101.902 96.519 lat band # 50 105.004 105.946 106.354 106.415 103.478 lat band # 51 111.681 108.159 108.452 104.052 102.599 file clr_sfc_down_daily_199207.ascii has been written Variable clr_sfc_up_Day = 14 lon # = 100 101 102 103 104 lat band # 45 6.298 7.498 7.498 7.036 7.036 lat band # 46 6.497 6.461 7.239 8.007 6.050 lat band # 47 5.969 5.497 5.450 11.691 13.973 lat band # 48 7.321 6.692 17.438 13.883 13.783 lat band # 49 5.642 18.300 15.977 13.105 11.855 lat band # 50 14.477 15.184 14.524 11.973 13.584 lat band # 51 15.620 12.473 9.498 7.881 11.627 file clr_sfc_up_daily_199207.ascii has been written Variable par_Day = 14 lon # = 100 101 102 103 104 lat band # 45 16.444 17.226 17.226 19.520 19.520 lat band # 46 20.134 19.981 20.480 21.586 22.095 lat band # 47 23.277 26.193 23.368 23.920 22.568 lat band # 48 26.644 28.128 25.687 24.898 25.463 lat band # 49 28.041 24.641 27.911 29.598 28.088 lat band # 50 27.811 29.001 31.478 30.059 34.277 lat band # 51 32.741 36.763 38.952 35.882 38.205 file par_daily_199207.ascii has been written Variable diff_par_Day = 14 lon # = 100 101 102 103 104 lat band # 45 16.444 17.224 17.224 19.513 19.513 lat band # 46 20.132 19.979 20.476 21.577 22.083 lat band # 47 23.245 26.078 23.349 23.898 22.555 lat band # 48 26.552 27.981 25.610 24.848 25.421 lat band # 49 27.945 24.621 27.809 29.403 27.249 lat band # 50 27.646 28.718 31.274 29.660 31.945 lat band # 51 32.531 33.562 35.027 34.734 35.862 file diff_par_daily_199207.ascii has been written Variable aer_opt_dep_Day = 14 lon # = 100 101 102 103 104 lat band # 45 0.128 0.127 0.127 0.127 0.127 lat band # 46 0.128 0.128 0.127 0.127 0.128 lat band # 47 0.128 0.128 0.128 0.125 0.124 lat band # 48 0.128 0.128 0.121 0.125 0.125 lat band # 49 0.127 0.119 0.124 0.126 0.249 lat band # 50 0.156 0.134 0.129 0.127 0.196 lat band # 51 0.116 0.190 0.180 0.303 0.364 file aer_opt_dep_daily_199207.ascii has been written Variable cld_opt_dep_Day = 14 lon # = 100 101 102 103 104 lat band # 45 7.260 6.766 6.766 5.160 5.160 lat band # 46 4.851 5.082 4.906 4.425 4.037 lat band # 47 3.950 2.539 3.986 3.789 4.547 lat band # 48 3.028 2.463 3.660 4.112 3.932 lat band # 49 2.776 4.784 3.395 2.812 3.799 lat band # 50 3.941 3.533 2.370 3.486 2.102 lat band # 51 2.815 1.806 1.157 1.926 1.322 file cld_opt_dep_daily_199207.ascii has been written Variable cld_frac_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 0.917 lat band # 50 1.000 1.000 1.000 1.000 0.889 lat band # 51 1.000 0.833 0.867 0.933 0.867 file cld_frac_daily_199207.ascii has been written Variable cos_sza_Day = 14 lon # = 100 101 102 103 104 lat band # 45 0.248 0.245 0.245 0.246 0.246 lat band # 46 0.261 0.258 0.259 0.259 0.256 lat band # 47 0.277 0.274 0.272 0.270 0.269 lat band # 48 0.287 0.289 0.286 0.286 0.284 lat band # 49 0.313 0.300 0.300 0.300 0.297 lat band # 50 0.326 0.325 0.328 0.310 0.309 lat band # 51 0.338 0.338 0.337 0.324 0.323 file cos_sza_daily_199207.ascii has been written Variable ave_cos_sza_Day = 14 lon # = 100 101 102 103 104 lat band # 45 0.243 0.240 0.240 0.237 0.237 lat band # 46 0.256 0.255 0.253 0.251 0.250 lat band # 47 0.269 0.268 0.266 0.265 0.263 lat band # 48 0.283 0.281 0.280 0.278 0.276 lat band # 49 0.296 0.294 0.293 0.291 0.289 lat band # 50 0.309 0.308 0.306 0.304 0.302 lat band # 51 0.322 0.321 0.319 0.317 0.315 file ave_cos_sza_daily_199207.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