SRB_REL3.0_SHORTWAVE_DAILY (binary) - GEWEX Shortwave Daily README file 1.0 Introduction This README file provides information on the SRB_REL3.0_SHORTWAVE_DAILY data set. The data set contains daily average global fields of eleven 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) 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 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. 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 3.0. 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 1998), with Pinker/Laszlo now the primary algorithm. Release 2.0: 12 year dataset (July 1983-October 1985), 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 include sunrise and 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. Release 3.0: Previous versions showed occasional instances of clear sky surface downward fluxes less than cloudy sky values at the same scene. This related to issues in the ISCCP DX radiance inputs to the algorithm. Now any 3-hourly period at any grid cell which shows an average TOA cloudy radiance less than the TOA clear sky radiance is considered a cell with a zero cloud fraction. The clear sky radiance is recalculated to include the cloudy sky values. Changes in the initial guess aerosol are made. The value of the surface albedo depends on the ISCCP DX clear sky composite radiance and the initial guess aerosol optical depth. Previously the initial guess depended only on surface type. Now the initial guess is from a monthly climatology of aerosols from the MATCH chemical transport model. In addition, the final aerosol optical depth calculated by the algorithm is capped at 0.05 over snow and ice. 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). All fluxes are in Watts per square meter. 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 thirteen 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 -3.9 W/m**2 (-2.2%, surface data higher), and the root mean square difference is 35.1 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. An assessment of the surface PAR fluxes with SURFRAD sites yields a mean bias of -2.3 W/m**2 and a root mean square difference of 14.5 W/m**2. 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 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 first 20.5 years 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. Starting in January 2005, ozone data was taken from the Stratosphere Monitoring Ozone Blended Analysis. 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 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. 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_rel3.0_shortwave_daily_(method)_yyyymm.binary, where srb Project name, Surface Radiation Budget rel3.0 Release number for these data (Release 3.0) shortwave Name of the algorithm, GEWEX Shortwave daily Time resolution of the data set (method) Averaging method, either utc or local 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 eleven 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 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: 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_srb_rel3_sw_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 (srb_rel3_sw_daily.nml). The input files are 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=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_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_daily read_srb_rel3_sw_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 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=infile,status='old',form='unformatted',access='direct',recl=4*nreg) should be modified to: open (10,file=infile,status='old',form='unformatted',access='direct',recl=nreg) The same should be done with the output binary file: open (15,file=outfile, form='unformatted', access='direct', & recl=nlon*nlat*4, status='replace') to: open (15,file=outfile, form='unformatted', access='direct', & recl=nlon*nlat, status='replace') 7.0 Sample Output The eleven 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). 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_rel3.0_shortwave_daily 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: support-asdc@earthdata.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * ***************************************************************** srb_rel3.0_shortwave_daily_local_199207.binary input file is opened Variable toa_down_Day = 14 lon # = 100 101 102 103 104 lat band # 45 123.367 123.367 123.367 123.367 123.367 lat band # 46 130.031 130.031 130.031 130.031 130.031 lat band # 47 136.711 136.711 136.711 136.711 136.711 lat band # 48 143.403 143.403 143.403 143.403 143.403 lat band # 49 150.100 150.100 150.100 150.100 150.100 lat band # 50 156.800 156.800 156.800 156.800 156.800 lat band # 51 163.497 163.497 163.497 163.497 163.497 file toa_down_daily_199207.ascii has been written Variable toa_up_Day = 14 lon # = 100 101 102 103 104 lat band # 45 68.536 67.387 67.387 63.182 63.182 lat band # 46 67.130 67.574 67.007 64.932 62.742 lat band # 47 66.039 60.052 66.707 63.863 62.288 lat band # 48 64.705 62.160 60.154 63.884 64.571 lat band # 49 70.663 70.932 64.628 61.522 64.008 lat band # 50 69.398 68.649 63.503 65.937 56.158 lat band # 51 64.491 54.771 51.933 58.286 52.182 file toa_up_daily_199207.ascii has been written Variable sfc_down_Day = 14 lon # = 100 101 102 103 104 lat band # 45 29.824 30.800 30.800 35.574 35.574 lat band # 46 36.897 36.594 37.484 39.879 42.828 lat band # 47 44.429 51.188 44.024 47.313 49.760 lat band # 48 51.926 54.817 58.634 53.658 52.469 lat band # 49 51.576 51.150 58.009 61.462 58.639 lat band # 50 58.328 59.416 65.198 62.388 72.947 lat band # 51 69.644 80.220 83.629 76.475 83.649 file sfc_down_daily_199207.ascii has been written Variable sfc_up_Day = 14 lon # = 100 101 102 103 104 lat band # 45 1.789 1.848 1.848 2.135 2.135 lat band # 46 2.214 2.196 2.249 2.393 3.370 lat band # 47 2.666 3.083 2.642 2.840 4.240 lat band # 48 3.124 3.306 6.128 4.154 3.152 lat band # 49 3.098 3.071 3.493 3.714 3.784 lat band # 50 3.539 3.620 3.940 3.809 4.764 lat band # 51 4.243 5.363 5.535 4.801 6.170 file sfc_up_daily_199207.ascii has been written Variable clr_toa_up_Day = 14 lon # = 100 101 102 103 104 lat band # 45 25.403 27.158 27.158 27.123 27.123 lat band # 46 26.906 26.923 27.964 28.926 27.329 lat band # 47 28.753 28.743 28.877 29.253 28.432 lat band # 48 31.406 31.276 31.488 29.345 29.632 lat band # 49 30.158 32.887 31.761 29.956 33.059 lat band # 50 29.822 31.839 29.374 29.933 34.229 lat band # 51 30.284 30.820 29.193 32.459 37.709 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 80.595 80.174 80.174 80.674 80.674 lat band # 46 85.474 85.460 85.799 86.013 85.971 lat band # 47 90.874 90.858 90.950 91.381 91.821 lat band # 48 96.232 96.259 96.265 96.787 97.245 lat band # 49 103.056 101.813 101.529 101.901 97.641 lat band # 50 108.569 108.257 108.103 107.015 104.443 lat band # 51 113.651 110.627 111.346 106.560 104.734 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 11.622 13.285 13.285 13.245 13.245 lat band # 46 12.696 12.491 13.522 14.415 12.538 lat band # 47 13.840 13.552 13.596 14.176 13.510 lat band # 48 16.056 15.773 15.848 13.845 14.426 lat band # 49 15.247 17.281 15.699 13.912 13.532 lat band # 50 14.593 16.385 13.441 13.328 15.435 lat band # 51 14.456 12.124 10.796 10.405 14.474 file clr_sfc_up_daily_199207.ascii has been written Variable par_Day = 14 lon # = 100 101 102 103 104 lat band # 45 14.635 15.071 15.071 17.203 17.203 lat band # 46 17.983 17.805 18.175 19.190 20.355 lat band # 47 21.407 24.241 21.141 22.555 23.458 lat band # 48 24.737 25.966 27.362 25.350 24.930 lat band # 49 24.826 24.598 27.515 28.933 27.516 lat band # 50 27.852 28.281 30.775 29.422 33.583 lat band # 51 32.876 36.885 38.174 35.264 37.839 file par_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 0.917 lat band # 47 1.000 1.000 1.000 1.000 0.875 lat band # 48 1.000 1.000 0.812 0.917 1.000 lat band # 49 1.000 1.000 1.000 1.000 0.887 lat band # 50 1.000 1.000 1.000 0.938 0.667 lat band # 51 0.917 0.708 0.700 0.700 0.692 file cld_frac_daily_199207.ascii has been written Variable cos_sza_Day = 14 lon # = 100 101 102 103 104 lat band # 45 0.190 0.189 0.189 0.193 0.193 lat band # 46 0.200 0.199 0.200 0.202 0.201 lat band # 47 0.212 0.211 0.210 0.210 0.211 lat band # 48 0.220 0.222 0.221 0.222 0.222 lat band # 49 0.238 0.231 0.232 0.233 0.232 lat band # 50 0.248 0.248 0.251 0.241 0.242 lat band # 51 0.258 0.258 0.258 0.252 0.252 file cos_sza_daily_199207.ascii has been written Variable ave_cos_sza_Day = 14 lon # = 100 101 102 103 104 lat band # 45 0.186 0.186 0.186 0.186 0.186 lat band # 46 0.197 0.197 0.197 0.197 0.197 lat band # 47 0.207 0.207 0.207 0.207 0.207 lat band # 48 0.217 0.217 0.217 0.217 0.217 lat band # 49 0.227 0.227 0.227 0.227 0.227 lat band # 50 0.237 0.237 0.237 0.237 0.237 lat band # 51 0.247 0.247 0.247 0.247 0.247 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