GEWEX Shortwave Monthly README file 1.0 Introduction This README file provides information on the SRB_REL2_SHORTWAVE_MONTHLY 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 Science Data Center (ASDC) Science, Users and Data Services Office at: 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: 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 Description of Sample Read Software 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 were first averaged into local solar time daily values (see README_SRB_REL2_GSW_DAILY.txt). The Daily averages were then averaged into monthly averages. The current version of the data sets 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 monthly 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 0.9 W/m**2 (estimate - observation), and the random error to be about +/- 22.0 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. All algorithms compute monthly averages from the Daily averaged fluxes. Thus, any discontinuity in the daily averaged fluxes will be averaged over the course of an entire month and are observed to persist. For Daily averaged fluxes any discontinuity in instantaneous fluxes will be exacerbated by the temporal gaps of coverage in the India 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: Paul.W.Stackhouse@nasa.gov Production Contact: Atmospheric Science Data Center User 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 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 ASCII data and are named according to the following convention: srb_rel2_shortwave_monthly_yyyymm.ascii, where srb Project name, Surface Radiation Budget rel2 Release number for these data (Release 2) shortwave Name of the algorithm, GEWEX Shortwave monthly Time resolution of the data set yyyy 4-digit year for these data mm 2-digit month for these data ascii file format 4.0 Science Parameters Information The files contain global fields of 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 550 Fill Values: -1000.0 Scale Factor: None Name: All Sky TOA Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 400 Fill Values: -1000.0 Scale Factor: None Name: All Sky Surface Downward SW Flux Units: Watts per square meter Type: Real Range: 0 to 425 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 250 Fill Values: -1000.0 Scale Factor: None Name: All Sky Surface Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 350 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky TOA Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 375 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky Surface Downward SW Flux Units: Watts per square meter Type: Real Range: 0 to 425 Fill Values: -1000.0 Scale Factor: None Name: Clear Sky Surface Upward SW Flux Units: Watts per square meter Type: Real Range: 0 to 350 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 125 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_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 (shortwave_monthly.nml). The input files are ASCII 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 ****' 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. / 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_monthly read_shortwave_monthly.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_monthly 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 is code run, the following information appears on the screen: ***************************************************************** * * * * * Data Set srb_rel2_shortwave_monthly Read Software * * * * Version: 1.0 * * * * Date: February 12, 2003 * * * * 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: larc@eos.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * ***************************************************************** srb_rel2_shortwave_monthly_199207.ascii input file is opened Variable toa_down_ lon # = 100 101 102 103 104 lat band # 45 126.300 126.300 126.300 126.300 126.300 lat band # 46 132.900 132.900 132.900 132.900 132.900 lat band # 47 139.600 139.600 139.600 139.600 139.600 lat band # 48 146.200 146.200 146.200 146.200 146.200 lat band # 49 152.800 152.800 152.800 152.800 152.800 lat band # 50 159.500 159.500 159.500 159.500 159.500 lat band # 51 166.100 166.100 166.100 166.100 166.100 file toa_down_monthly_199207.ascii has been written Variable toa_up_ lon # = 100 101 102 103 104 lat band # 45 49.800 51.800 51.800 49.800 49.800 lat band # 46 53.200 54.700 54.500 52.800 52.500 lat band # 47 52.900 53.500 53.700 58.600 57.200 lat band # 48 54.700 54.900 61.500 58.600 58.100 lat band # 49 56.300 64.000 61.000 57.800 58.800 lat band # 50 60.100 60.500 58.200 58.000 57.400 lat band # 51 59.400 57.000 57.700 59.500 60.300 file toa_up_monthly_199207.ascii has been written Variable sfc_down_ lon # = 100 101 102 103 104 lat band # 45 54.500 52.300 52.300 54.400 54.400 lat band # 46 56.300 54.800 54.900 56.700 56.800 lat band # 47 61.900 61.300 61.200 56.500 58.000 lat band # 48 65.900 65.700 59.100 62.300 62.900 lat band # 49 69.700 61.900 65.600 68.800 68.300 lat band # 50 71.700 71.500 74.100 74.500 75.800 lat band # 51 78.900 81.700 80.000 78.200 78.100 file sfc_down_monthly_199207.ascii has been written Variable sfc_diff_ lon # = 100 101 102 103 104 lat band # 45 46.600 47.400 47.400 48.700 48.700 lat band # 46 49.800 49.400 50.600 49.200 50.100 lat band # 47 52.500 53.400 54.000 49.900 50.500 lat band # 48 57.100 56.400 53.800 54.700 54.500 lat band # 49 60.500 57.700 57.400 57.700 56.800 lat band # 50 62.300 62.200 61.000 61.600 58.800 lat band # 51 64.800 64.100 67.000 65.100 63.900 file sfc_diff_monthly_199207.ascii has been written Variable sfc_up_ lon # = 100 101 102 103 104 lat band # 45 3.500 3.400 3.400 3.400 3.400 lat band # 46 3.500 3.500 3.400 3.600 3.400 lat band # 47 3.800 3.800 3.700 4.200 4.400 lat band # 48 4.300 4.100 4.500 4.700 4.700 lat band # 49 4.200 4.300 5.300 5.200 5.400 lat band # 50 5.300 5.300 5.700 5.500 6.100 lat band # 51 6.000 6.300 5.200 5.300 6.100 file sfc_up_monthly_199207.ascii has been written Variable clr_toa_up_ lon # = 100 101 102 103 104 lat band # 45 23.700 24.600 24.600 23.200 23.200 lat band # 46 23.700 24.000 23.900 24.200 24.500 lat band # 47 24.900 24.300 23.800 31.200 31.400 lat band # 48 26.000 24.800 33.800 32.000 31.500 lat band # 49 25.100 34.700 34.700 31.500 31.800 lat band # 50 34.100 34.800 33.200 31.500 32.900 lat band # 51 34.500 32.900 30.100 31.100 34.000 file clr_toa_up_monthly_199207.ascii has been written Variable clr_sfc_down_ lon # = 100 101 102 103 104 lat band # 45 82.500 82.500 82.500 83.400 83.400 lat band # 46 87.500 88.500 88.300 88.100 88.600 lat band # 47 92.200 92.300 92.700 92.200 91.200 lat band # 48 97.300 98.100 96.900 97.200 96.800 lat band # 49 102.100 102.500 100.400 101.500 102.300 lat band # 50 104.900 103.900 104.000 106.800 107.900 lat band # 51 110.400 110.800 111.400 110.700 111.000 file clr_sfc_down_monthly_199207.ascii has been written Variable clr_sfc_up_ lon # = 100 101 102 103 104 lat band # 45 6.800 7.800 7.800 7.000 7.000 lat band # 46 6.300 7.600 7.300 7.400 8.100 lat band # 47 6.900 6.500 6.300 13.900 13.300 lat band # 48 7.800 7.200 16.000 14.200 13.300 lat band # 49 6.000 16.900 15.300 12.600 13.500 lat band # 50 13.400 13.500 11.800 12.100 14.400 lat band # 51 13.600 12.100 9.500 10.100 13.500 file clr_sfc_up_monthly_199207.ascii has been written Variable par_ lon # = 100 101 102 103 104 lat band # 45 24.700 24.000 24.000 24.900 24.900 lat band # 46 25.800 25.300 25.400 26.100 26.200 lat band # 47 28.300 28.200 28.200 26.200 26.800 lat band # 48 30.400 30.300 27.600 29.000 29.200 lat band # 49 32.200 29.000 30.400 31.800 31.600 lat band # 50 33.100 33.000 34.100 34.300 34.800 lat band # 51 36.300 37.400 36.800 36.100 36.000 file par_monthly_199207.ascii has been written Variable diff_par_ lon # = 100 101 102 103 104 lat band # 45 21.600 22.100 22.100 22.700 22.700 lat band # 46 23.300 23.200 23.700 23.200 23.600 lat band # 47 24.800 25.200 25.400 23.700 24.000 lat band # 48 26.900 26.600 25.600 26.000 25.900 lat band # 49 28.500 27.300 27.300 27.500 27.200 lat band # 50 29.500 29.400 29.000 29.200 28.100 lat band # 51 30.600 30.500 31.600 30.900 30.400 file diff_par_monthly_199207.ascii has been written Variable aer_opt_dep_ lon # = 100 101 102 103 104 lat band # 45 0.160 0.160 0.160 0.150 0.150 lat band # 46 0.170 0.130 0.140 0.150 0.150 lat band # 47 0.170 0.160 0.160 0.190 0.240 lat band # 48 0.180 0.150 0.190 0.200 0.200 lat band # 49 0.180 0.180 0.250 0.230 0.180 lat band # 50 0.280 0.330 0.310 0.200 0.180 lat band # 51 0.280 0.250 0.220 0.240 0.260 file aer_opt_dep_monthly_199207.ascii has been written Variable cld_opt_dep_ lon # = 100 101 102 103 104 lat band # 45 3.160 3.330 3.330 2.850 2.850 lat band # 46 3.080 3.450 3.340 3.300 3.310 lat band # 47 2.960 2.870 2.980 4.320 4.210 lat band # 48 2.570 2.770 4.100 3.590 3.780 lat band # 49 2.500 4.260 4.060 3.310 3.700 lat band # 50 3.190 3.270 3.160 3.030 3.280 lat band # 51 2.570 2.510 2.640 3.310 3.720 file cld_opt_dep_monthly_199207.ascii has been written Variable cld_frac_ lon # = 100 101 102 103 104 lat band # 45 0.871 0.899 0.899 0.902 0.902 lat band # 46 0.890 0.916 0.927 0.864 0.894 lat band # 47 0.833 0.847 0.879 0.872 0.826 lat band # 48 0.871 0.866 0.892 0.862 0.847 lat band # 49 0.882 0.925 0.836 0.832 0.831 lat band # 50 0.814 0.830 0.788 0.823 0.790 lat band # 51 0.789 0.777 0.834 0.798 0.794 file cld_frac_monthly_199207.ascii has been written Variable cos_sza_ lon # = 100 101 102 103 104 lat band # 45 0.260 0.253 0.253 0.252 0.252 lat band # 46 0.274 0.267 0.267 0.268 0.265 lat band # 47 0.288 0.286 0.282 0.279 0.278 lat band # 48 0.302 0.302 0.297 0.297 0.293 lat band # 49 0.319 0.312 0.313 0.312 0.307 lat band # 50 0.334 0.329 0.328 0.324 0.320 lat band # 51 0.346 0.346 0.342 0.339 0.337 file cos_sza_monthly_199207.ascii has been written Variable ave_cos_sza_ lon # = 100 101 102 103 104 lat band # 45 0.251 0.249 0.249 0.245 0.245 lat band # 46 0.264 0.263 0.261 0.260 0.258 lat band # 47 0.277 0.276 0.275 0.273 0.271 lat band # 48 0.291 0.289 0.288 0.286 0.284 lat band # 49 0.304 0.302 0.301 0.299 0.297 lat band # 50 0.317 0.315 0.314 0.312 0.310 lat band # 51 0.330 0.328 0.327 0.325 0.323 file ave_cos_sza_monthly_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