SRB_REL2.8_SHORTWAVE_3HRLYMONTHLY GEWEX Shortwave 3-hourly/monthly README file 1.0 Introduction This README file provides information on the SRB_REL2.8_SHORTWAVE_3HRLYMONTHLY data set. The data set contains monthly average/3-hourly (also called diurnally-resolved monthly average or just 'diurnal' for brevity) global fields of 11 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 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 2.2 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 2.8. Version History: Release 1.0: 8 year dataset (July 1983-June 1991) on 2.5 degree equal angle grid using ISCCP C1 data and algorithm of Darnell et al. (1992) Release 1.1: 4 year dataset (March 1985-December 1988), with Pinker/Laszlo now the primary algorithm. Release 2.0: 12 year dataset (July 1983-October 1995), on nested grid (described in Section 2.3), using ISCCP DX pixel data. Release 2.5: Atmospheric transmissivity/reflectivity lookup tables extended to cosine solar zenith angles as low as 0.01. Revamping of the methodology used to fill data gaps. These changes allowed data to be computed for locations with low sun angles the entire month (polar twilight areas). Release 2.6: Improvement of the TOA insolation calculation. Previously each January 1 the Earth began in the same orbital point. Leap years were handled by making day 366 a duplicate of day 1. The new scheme was a Julian day based approach from the Astronomical Almanac. Release 2.7: The effective solar constant was increased to 1367 W/m2 from 1359 W/m2, for consistency with other products. The Pinker/Laszlo algorithm computes radiation in the range from 0.2-4.0 microns. That does not cover the full range of solar output, which extends past 4 microns. The extra energy was placed in the 0.7-4.0 micron band. A bug was fixed which had incorrectly handled the treatment of 3-hourly time periods with low sun angles. This has had the effect of increasing the extent of the solar terminator. Lookup tables for atmospheres at altitude were constructed and added. Surface fluxes at non sea level elevations are now increased. Release 2.81: Further improvement was made to the treatment of 3-hourly periods which bracket sunrise or sunset. There are minor improvements in the treatment of filling gaps in the input data. Several new output fields were added for diagnostic use by the SRB group. There are a total of 11 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 Upward Flux 5. Clear Sky TOA Upward Flux 6. Clear Sky Surface Downward Flux 7. Clear Sky Surface Upward Flux 8. All Sky Global Photosynthetically Active Radiative Flux (PAR) 9. Cloud Fraction 10. Cosine Solar Zenith Angle from Satellite 11. 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). 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 fourteen years (1992-2005) 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 -12.3 W/m**2 (-4.1%, surface data higher), and the root mean square difference is 46.5 W/m**2. Uncertainties associated with with operational BSRN measurements during this period are believed to be about +/- 5-15 W/m**2 (Ellsworth Dutton, NOAA, BSRN Manager). 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 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. Documentation and Validation of the Goddard Earth Observing System (GEOS) Data Assimilation System - Version 4 . Technical Report Series on Global Modeling and Data Assimilation 104606 , 26 http://gmao.gsfc.nasa.gov/pubs/docs/Bloom168.pdf) Column ozone values for the entire duration of this dataset (July 1983 to December 2004) were obtained primarily from the Total Ozone Mapping Spectrometer (TOMS) archive. For the early period (July 1983-November 1994), TOMS data came from NIMBUS-7 and Meteor-3 satellites. There was an interruption of about 20 months (December 1994-July 1996) after which TOMS data from EP-TOMS became available in August 1996 and continued until December 2004. 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. 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 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 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_rel2.8_shortwave_3hrlymonthly_yyyymm.binary, where srb Project name, Surface Radiation Budget rel2.8 Release number for these data (Release 2.8) 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 eleven 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 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: 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 direct-access binary on the nested (44016 box) grid. The software reads one or more of the 11 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_up=.true. clr_toa_up=.true. clr_sfc_down=.true. clr_sfc_up=.true. par=.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 With namelist values of: &time_vars yr=1992 mon=7 ascii=.true. binary=.false. path_in='' path_out='' little_endian=.false. gmt=.true. toa_down=.true. toa_up=.true. sfc_down=.true. sfc_up=.true. clr_toa_up=.true. clr_sfc_down=.true. clr_sfc_up=.true. par=.true. cld_frac=.true. cos_sza=.true. ave_cos_sza=.true. / Eleven tables of numbers are printed to the screen. These 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). The output to the screen also indicates that ascii files of the 1x1 global parameters were produced. ***************************************************************** * * * * * Data Set srb_rel2.8_shortwave_3hrlymonthly 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: larc@eos.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * ***************************************************************** srb_rel2.8_shortwave_3hrlymonthly_199207.binary input file is opened cell_longitudes.dat is opened Variable toa_down_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 497.606 493.271 493.271 487.890 487.890 lat band # 46 517.139 514.916 512.432 509.690 506.703 lat band # 47 537.545 535.287 532.761 529.984 526.926 lat band # 48 557.803 555.510 552.945 550.100 547.010 lat band # 49 577.887 575.542 572.939 570.058 566.923 lat band # 50 597.771 595.416 592.768 589.848 586.655 lat band # 51 617.503 615.103 612.423 609.448 606.210 file toa_down_3hrlymonthly_199207.ascii has been written Variable toa_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 181.071 187.064 187.064 184.000 184.000 lat band # 46 191.923 198.042 198.594 190.790 197.113 lat band # 47 190.377 197.026 190.729 207.039 198.645 lat band # 48 196.061 193.052 213.452 197.361 199.835 lat band # 49 201.587 220.594 206.916 194.735 199.223 lat band # 50 208.771 202.761 186.990 195.887 197.655 lat band # 51 198.687 176.684 179.929 196.410 203.965 file toa_up_3hrlymonthly_199207.ascii has been written Variable sfc_down_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 232.758 222.626 222.626 221.135 221.135 lat band # 46 236.613 228.668 225.913 232.410 222.735 lat band # 47 255.287 246.610 251.184 233.345 239.439 lat band # 48 267.826 269.129 245.713 262.035 256.810 lat band # 49 278.671 257.790 270.723 282.103 275.632 lat band # 50 290.213 295.690 309.426 298.507 297.084 lat band # 51 322.174 340.806 333.287 313.436 305.216 file sfc_down_3hrlymonthly_199207.ascii has been written Variable sfc_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 14.423 14.084 14.084 13.687 13.687 lat band # 46 13.906 14.177 13.768 14.371 13.687 lat band # 47 15.200 14.806 14.648 16.248 17.029 lat band # 48 16.465 16.319 16.619 18.455 18.442 lat band # 49 15.868 17.306 19.145 19.548 19.765 lat band # 50 19.565 20.526 20.419 19.861 22.784 lat band # 51 23.506 21.074 19.248 19.042 21.668 file sfc_up_3hrlymonthly_199207.ascii has been written Variable clr_toa_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 78.013 82.558 82.558 79.035 79.035 lat band # 46 74.687 78.258 77.684 80.277 81.826 lat band # 47 78.555 78.742 74.952 99.623 100.094 lat band # 48 81.203 78.239 104.287 100.477 101.523 lat band # 49 75.452 108.023 106.874 98.539 98.616 lat band # 50 105.429 105.142 98.790 92.513 102.900 lat band # 51 104.723 89.139 84.242 89.223 99.819 file clr_toa_up_3hrlymonthly_199207.ascii has been written Variable clr_sfc_down_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 346.194 341.052 341.052 339.113 339.113 lat band # 46 362.397 362.277 360.277 356.539 355.181 lat band # 47 377.948 376.110 374.603 371.658 361.597 lat band # 48 397.474 396.919 389.900 386.061 381.497 lat band # 49 413.619 412.223 400.648 402.271 402.287 lat band # 50 422.390 421.258 414.426 423.545 422.671 lat band # 51 445.152 439.748 437.545 433.845 438.203 file clr_sfc_down_3hrlymonthly_199207.ascii has been written Variable clr_sfc_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 23.532 27.584 27.584 25.906 25.906 lat band # 46 19.955 25.358 24.629 26.055 28.784 lat band # 47 22.681 22.852 19.145 45.413 40.200 lat band # 48 26.952 24.613 49.055 43.681 43.252 lat band # 49 19.132 54.887 46.419 40.390 42.687 lat band # 50 44.590 44.794 34.274 36.400 49.268 lat band # 51 47.306 27.726 22.594 27.213 44.368 file clr_sfc_up_3hrlymonthly_199207.ascii has been written Variable par_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 106.313 102.339 102.339 102.158 102.158 lat band # 46 109.461 106.310 105.335 107.294 103.723 lat band # 47 117.865 114.700 116.358 108.739 110.390 lat band # 48 124.610 124.884 115.148 121.584 119.045 lat band # 49 129.639 121.426 125.771 130.303 127.745 lat band # 50 135.064 136.868 141.658 137.810 137.010 lat band # 51 148.526 155.081 152.929 144.716 141.306 file par_3hrlymonthly_199207.ascii has been written Variable cld_frac_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 0.863 0.885 0.885 0.929 0.929 lat band # 46 0.905 0.925 0.957 0.860 0.946 lat band # 47 0.855 0.897 0.903 0.892 0.823 lat band # 48 0.919 0.893 0.911 0.871 0.839 lat band # 49 0.866 0.936 0.847 0.839 0.836 lat band # 50 0.863 0.837 0.758 0.831 0.812 lat band # 51 0.801 0.704 0.819 0.813 0.838 file cld_frac_3hrlymonthly_199207.ascii has been written Variable cos_sza_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 0.389 0.386 0.386 0.386 0.386 lat band # 46 0.405 0.399 0.401 0.402 0.401 lat band # 47 0.420 0.418 0.415 0.413 0.413 lat band # 48 0.434 0.436 0.431 0.432 0.429 lat band # 49 0.451 0.446 0.447 0.448 0.444 lat band # 50 0.466 0.462 0.464 0.460 0.458 lat band # 51 0.478 0.479 0.478 0.476 0.476 file cos_sza_3hrlymonthly_199207.ascii has been written Variable ave_cos_sza_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 0.376 0.373 0.373 0.368 0.368 lat band # 46 0.391 0.389 0.387 0.385 0.383 lat band # 47 0.406 0.404 0.402 0.400 0.398 lat band # 48 0.421 0.420 0.418 0.415 0.413 lat band # 49 0.436 0.435 0.433 0.431 0.428 lat band # 50 0.452 0.450 0.448 0.446 0.443 lat band # 51 0.466 0.465 0.463 0.460 0.458 file ave_cos_sza_3hrlymonthly_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