SRB_REL3.0_SHORTWAVE_3HRLYMONTHLY GEWEX Shortwave 3-hourly/monthly README file 1.0 Introduction This README file provides information on the SRB_REL3.0_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 Science Data Center (ASDC) User 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: 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 (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 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). 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 fifteen years (1992-2006) 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 -4.9 W/m**2 (-1.8%, surface data higher), and the root mean square difference is 42.7 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 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 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_rel3.0_shortwave_3hrlymonthly_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 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 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_rel3.0_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: support-asdc@earthdata.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * ***************************************************************** srb_rel3.0_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 # 45 481.961 477.711 477.711 472.478 472.478 lat band # 46 500.918 498.755 496.342 493.680 490.769 lat band # 47 520.692 518.493 516.039 513.331 510.370 lat band # 48 540.308 538.072 535.578 532.826 529.817 lat band # 49 559.759 557.488 554.954 552.158 549.102 lat band # 50 579.040 576.734 574.161 571.323 568.219 lat band # 51 598.144 595.804 593.193 590.313 587.164 file toa_down_3hrlymonthly_199207.ascii has been written Variable toa_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 185.079 195.214 195.214 189.241 189.241 lat band # 46 199.090 204.652 204.162 199.267 202.217 lat band # 47 199.475 204.098 198.429 202.139 193.082 lat band # 48 203.426 201.530 208.589 192.359 194.552 lat band # 49 212.396 215.186 202.016 189.979 196.928 lat band # 50 205.506 198.029 184.246 192.861 194.101 lat band # 51 194.194 175.689 177.612 195.507 200.743 file toa_up_3hrlymonthly_199207.ascii has been written Variable sfc_down_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 217.443 201.537 201.537 203.122 203.122 lat band # 46 216.913 208.773 206.733 211.016 204.454 lat band # 47 232.778 226.350 230.449 224.755 232.170 lat band # 48 246.555 248.143 236.247 253.187 248.668 lat band # 49 254.489 248.244 260.982 272.686 263.621 lat band # 50 278.270 285.518 297.459 287.010 287.428 lat band # 51 312.628 326.720 320.998 299.717 293.943 file sfc_down_3hrlymonthly_199207.ascii has been written Variable sfc_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 15.932 14.247 14.247 13.801 13.801 lat band # 46 15.025 14.421 13.519 15.382 13.906 lat band # 47 16.576 15.817 15.722 15.978 17.224 lat band # 48 17.424 18.575 16.075 18.258 18.608 lat band # 49 18.141 16.776 18.774 19.891 19.747 lat band # 50 19.444 20.444 20.686 20.242 24.388 lat band # 51 24.657 21.751 20.194 19.969 22.282 file sfc_up_3hrlymonthly_199207.ascii has been written Variable clr_toa_up_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 86.157 93.387 93.387 92.054 92.054 lat band # 46 86.183 90.906 91.648 96.318 95.104 lat band # 47 94.685 95.800 91.476 95.168 96.072 lat band # 48 100.504 99.105 98.095 95.489 98.541 lat band # 49 95.580 102.424 102.145 96.378 96.289 lat band # 50 101.715 100.411 96.681 91.636 103.747 lat band # 51 101.736 88.200 85.467 90.269 100.846 file clr_toa_up_3hrlymonthly_199207.ascii has been written Variable clr_sfc_down_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 344.418 336.408 336.408 334.205 334.205 lat band # 46 359.551 360.017 357.374 349.580 349.786 lat band # 47 370.514 368.546 368.520 367.573 357.991 lat band # 48 391.656 391.310 384.417 381.510 377.295 lat band # 49 407.891 406.562 393.967 394.835 398.533 lat band # 50 416.383 416.256 406.753 417.033 415.536 lat band # 51 439.534 432.919 430.018 427.636 431.034 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 41.550 46.181 46.181 46.524 46.524 lat band # 46 41.162 48.147 48.281 48.764 49.678 lat band # 47 45.796 46.748 43.489 48.534 44.036 lat band # 48 55.019 54.431 49.601 46.253 48.249 lat band # 49 48.620 56.426 48.045 44.269 49.115 lat band # 50 48.339 48.189 38.471 42.802 56.949 lat band # 51 52.603 34.356 31.033 36.381 52.538 file clr_sfc_up_3hrlymonthly_199207.ascii has been written Variable par_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 99.681 93.424 93.424 94.296 94.296 lat band # 46 100.984 97.632 96.958 97.960 95.742 lat band # 47 108.090 105.828 107.338 104.859 107.066 lat band # 48 115.437 115.855 110.864 117.548 115.309 lat band # 49 119.354 117.021 121.307 125.706 122.577 lat band # 50 129.752 132.292 136.358 132.646 132.357 lat band # 51 144.137 149.099 147.390 138.773 136.123 file par_3hrlymonthly_199207.ascii has been written Variable cld_frac_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 0.837 0.875 0.875 0.900 0.900 lat band # 46 0.877 0.896 0.927 0.833 0.917 lat band # 47 0.828 0.869 0.875 0.865 0.797 lat band # 48 0.891 0.865 0.883 0.844 0.812 lat band # 49 0.852 0.906 0.820 0.781 0.820 lat band # 50 0.836 0.819 0.734 0.805 0.734 lat band # 51 0.760 0.703 0.781 0.800 0.807 file cld_frac_3hrlymonthly_199207.ascii has been written Variable cos_sza_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 0.377 0.374 0.374 0.374 0.374 lat band # 46 0.392 0.386 0.388 0.390 0.388 lat band # 47 0.407 0.405 0.402 0.400 0.400 lat band # 48 0.421 0.422 0.417 0.418 0.415 lat band # 49 0.437 0.432 0.433 0.434 0.430 lat band # 50 0.451 0.448 0.449 0.446 0.444 lat band # 51 0.463 0.465 0.463 0.461 0.461 file cos_sza_3hrlymonthly_199207.ascii has been written Variable ave_cos_sza_ Hour = 06 lon # = 100 101 102 103 104 lat band # 45 0.364 0.361 0.361 0.357 0.357 lat band # 46 0.378 0.377 0.375 0.373 0.371 lat band # 47 0.393 0.392 0.390 0.388 0.386 lat band # 48 0.408 0.406 0.405 0.402 0.400 lat band # 49 0.423 0.421 0.419 0.417 0.415 lat band # 50 0.437 0.436 0.434 0.432 0.429 lat band # 51 0.452 0.450 0.448 0.446 0.444 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