B_REL3.0_QCSW_MONTHLY - GEWEX Quality-Check Monthly Shortwave README File 1.0 Introduction This README file provides information on the SRB_REL3.0_QCSW_MONTHLY data set. The data set contains monthly average global fields of six shortwave (SW) surface radiative parameters derived with the Quality-Check SW (QCSW) 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 parameters contained in these files are: 1. Top-of-atmosphere (TOA)insolation (FTOA) 2. Pristine-sky surface insolation (FPRS) 3. Clear-sky surface insolation (FCLR) 4. All-sky surface insolation (FALL) 5. Surface absorbed SW flux (FABS) 6. All-sky surface albedo (SALB) These parameters were derived originally on a daily temporal resolution. Monthly averages were computed from the daily values. The current version of the data sets is identified as Release 3.0. It covers a period of 24.5 years from July 1983 to December 2007. Detailed description of the algorithm used in deriving these parameters can be found in: Gupta et al. (2001) - NASA/TP-2001-211272, Dec. 2001, 31 pp. (available on the web at http://techreports.larc.nasa.gov/ltrs/ltrs.html) Darnell et al. (1992) - J. Geophys. Res., 97, 15741-15760. Darnell et al. (1988) - J. Climate, 1, 820-835. 2.0.1. Improvements over the algorithm described in the above references. The algorithm used for producing the current dataset differs from the one described in the above references in the following important regards: (a) Broadband aerosol optical properties used for the current data set were derived using aerosol optical depths from the Model of Atmospheric Transport and Chemistry (MATCH; Rasch, Collins,and Eaton,2001: JGR-Atmospheres, 106, 7337-7355) assimilation products and single scattering albedo and asymmetry parameter from the Optical Properties of Aerosols and Clouds (OPAC; Hess, Koepke, and Schult, 1998: BAMS, 79, 831-844) database. Aerosol properties used in earlier versions of this data set were based on the information provided in Deepak and Gerber (1983; Report of the experts' meeting on aerosols and their climatic effects. WCP-55, 107 pp.) (b) Monthly climatological top-of-atmosphere clear-sky albedos used for the current data set were derived from 70 months (March 2000 - December 2005) of CERES data from the Terra satellite. Corresponding data used in earlier versions of this data set were based on 5 years (1985-1989) of Earth Radiation Budget Experiment (ERBE) measurements. (c) The 4-class (ocean/coast/land/desert) surface type map used for the current data set was derived from the 1/6 deg. surface type map from the International Geosphere-Biosphere Program (IGBP). Corresponding map used in earlier versions of this data set was developed for ERBE processing from older information. (d) TOA insolation computation method used in earlier versions of this data set was based on approximate relations presented in Iqbal (1983) in the interest of simplicity and speed. For the current release, TOA insoaltion is computed using the astronomical almanac algorithm of Michalsky (1988). 2.1 Data Quality For information on validation of these products, the user is referred to the Data Quality Summary available at: http://gewex-srb.larc.nasa.gov/ 2.1.1 Calibration shifts The SRB algorithms rely heavily on radiances and cloud properties from ISCCP. Great care is taken by the ISCCP team to produce a well-calibrated, homogeneous dataset from dozens of satellites over the course of several decades. However, there are a few known issues and discontinuities in the ISCCP products which are likely to be reflected in SRB products. ISCCP uses a reference afternoon polar orbiter as a calibration standard for the other satellites (geostationary and polar orbiting) in the constellation. The afternoon orbiters are subject to orbital drift and are replaced every few years. The dates of transition from one reference satellite to the next are the dates where small discontinuities in the SRB products are possible. The transition dates are as follows: February 1, 1985: NOAA-7 replaced by NOAA-9 November 1, 1988: NOAA-9 replaced by NOAA-11 September 30, 1994: NOAA-11 goes out of service February 1, 1995: NOAA-14 goes into service For the October 1994-January 1995 timeframe there was no reference orbiter available, so an interpolation between NOAA-11 and NOAA-14 is used. SRB results show noticeable anomalies in this period, some of which are likely artifacts of the calibration situation. October 1, 2001: NOAA-14 replaced by NOAA-16 January 1, 2006: NOAA-16 replaced by NOAA-18 From NOAA-16 onward, the visible calibration is bi-linear, which has led to some changes from the previous linear calibrations. The 2001 transition to NOAA-16 is accompanied by fairly strong radiance increases over ice, which has led to polar values of SRB surface albedo and cloud optical thickness which are probably anomalously high, and surface downward fluxes which may be too low. The NOAA-18 calibration appears to be raising overall reported visible radiances, especially reducing the frequency of very low radiance scenes, such as clear skies over ocean near the day-night terminator. The effect on SRB products from 2006 onward has been mainly to cause a jump in surface albedo over much of the planet. Surface downward fluxes are less affected. Care should be taken when computing long term time series from SRB data, with special notice taken of known transition dates, including those noted in Section 2.1.2 below. 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. 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. 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 most of the 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. Column ozone data contimued to be available beyond December 2004 from OMI instrument aboard Aura satellite but TOVS data, which is essential for filling the gaps in OMI data, developed some unexplained gaps of its own and became unusable. Beginning in January 2005, GEWEX/SRB started using a daily analysis ozone product from NOAA Climate Predictions Center (CPC), known as the Stratospheric Monitoring-group Ozone Blended Analysis (SMOBA). Surface albedos are derived with a parameterization using monthly climatological clear-sky TOA albedos which are based on 46 months of CERES terra observations. 2.3 Grid Description The grid on which these fluxes are originally computed is a quasi-equal-area grid consisting of 44016 cells. The cell size is 1 deg. in latitude throughout and 1 deg. in longitude between 45N and 45S. Poleward of these latitudes, the cell size is progressively increased in longitude to accommodate a sufficient number of 30 km ISCCP pixels in each cell. This grid is also called the "nested grid." A detailed description of the grid is also presented in the Data Quality Summary. The read software described below contains a subroutine to regrid the fluxes to a 1 degree latitude by 1 degree longitude equal-angle grid using replication. 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 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_qcsw_monthly_yyyymm.binary, where srb Project name, Surface Radiation Budget rel3.0 Release number for these data (Release 3.0) qcsw Name of the algorithm, Quality-Check Shortwave monthly 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 monthly averages of the following parameters on the nested grid. Each file has 7 records, containing one global field in each record. Name: Top-of-Atmosphere (TOA) Downward SW Flux (FTOA) Name: Top-of-Atmosphere Insolation Units: Watts per square meter Type: Real Range: 0 to 700. Fill Values: -999.0 Scale Factor: None Name: Pristine-Sky Surface Downward SW Flux (FPRS) or Pristine-Sky Surface Insolation Units: Watts per square meter Type: Real Range: 0 to 600. Fill Values: -999.0 Scale Factor: None Name: Clear-Sky Surface Downward SW Flux (FCLR) or Clear-Sky Surface Insolation Units: Watts per square meter Type: Real Range: 0 to 600. Fill Values: -999.0 Scale Factor: None Name: All-Sky Surface Downward SW Flux (FALL) or All-Sky Surface Insolation Units: Watts per square meter Type: Real Range: 0 to 500. Fill Values: -999.0 Scale Factor: None Name: Surface Absorbed SW Flux (FABS) or Surface Net SW Flux Units: Watts per square meter Type: Real Range: 0 to 500. Fill Values: -999.0 Scale Factor: None Name: All-Sky Surface Albedo (SALB) Units: No units. It is a fraction. Type: Real Range: 0 to 1.0 Fill Values: -999.0 Scale Factor: None 5.0 Sample Read Software Description Sample read software written in Fortran-90, read_srb_rel3_qcsw_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 (srb_rel3_qcsw_monthly.nml). The input files are direct-access binary on the nested (44016 box) grid. The software reads one or more of the 6 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=.false. FTOA=.true. FPRS=.true. FCLR=.true. FALL=.true. FABS=.true. SALB=.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 IBM P6 machine 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_qcsw_monthly read_srb_rel3_qcsw_monthly.f90 The providers used a GFORTRAN F90 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_qcsw_monthly 7.0 Sample Output When the is code run, the following information appears on the screen: The tables of numbers below show the values of each of the parameters read from the 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. ***************************************************************** * * * * * Data Set srb_rel3.0_qcsw_monthly Read Software * * * * Version: 1.0 * * * * Contact: 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 * * * ***************************************************************** srb_rel3.0_qcsw_monthly_199207.binary input file is opened Variable FTOA_ lon # = 100 101 102 103 104 lat band # 45 127.714 127.714 127.714 127.714 127.714 lat band # 46 134.379 134.379 134.379 134.379 134.379 lat band # 47 141.056 141.056 141.056 141.056 141.056 lat band # 48 147.741 147.741 147.741 147.741 147.741 lat band # 49 154.428 154.428 154.428 154.428 154.428 lat band # 50 161.113 161.113 161.113 161.113 161.113 lat band # 51 167.793 167.793 167.793 167.793 167.793 file FTOA_monthly_199207.ascii has been written Variable FPRS_ lon # = 100 101 102 103 104 lat band # 45 88.895 88.818 88.818 88.782 88.782 lat band # 46 93.847 93.807 93.799 93.801 93.799 lat band # 47 98.909 98.907 98.890 98.873 98.905 lat band # 48 104.073 104.068 104.032 104.046 104.080 lat band # 49 109.302 109.273 109.266 109.310 109.323 lat band # 50 114.621 114.613 114.626 114.650 114.632 lat band # 51 120.043 120.021 120.000 119.975 119.951 file FPRS_monthly_199207.ascii has been written Variable FCLR_ lon # = 100 101 102 103 104 lat band # 45 85.156 84.977 84.977 84.851 84.851 lat band # 46 89.975 89.880 89.832 89.803 89.791 lat band # 47 94.857 94.843 94.814 94.793 94.853 lat band # 48 99.895 99.895 99.860 99.904 99.988 lat band # 49 105.095 105.046 105.045 105.140 105.213 lat band # 50 110.405 110.392 110.416 110.487 110.536 lat band # 51 115.844 115.851 115.856 115.861 115.887 file FCLR_monthly_199207.ascii has been written Variable FALL_ lon # = 100 101 102 103 104 lat band # 45 38.906 33.475 33.475 33.700 33.700 lat band # 46 36.347 30.842 31.957 35.388 38.566 lat band # 47 39.215 39.805 38.938 40.569 45.834 lat band # 48 43.220 43.191 42.546 47.967 49.865 lat band # 49 46.413 44.176 50.659 55.898 55.481 lat band # 50 53.945 56.352 61.153 62.684 64.549 lat band # 51 63.903 67.098 68.105 66.832 67.346 file FALL_monthly_199207.ascii has been written Variable FABS_ lon # = 100 101 102 103 104 lat band # 45 35.381 30.592 30.592 30.779 30.779 lat band # 46 33.147 28.266 29.268 32.335 35.141 lat band # 47 35.823 36.377 35.577 37.051 41.718 lat band # 48 39.515 39.373 39.018 43.780 45.428 lat band # 49 42.427 40.513 46.380 50.888 50.600 lat band # 50 49.370 51.480 55.738 57.067 58.678 lat band # 51 58.344 61.127 62.063 60.952 61.345 file FABS_monthly_199207.ascii has been written Variable SALB_ lon # = 100 101 102 103 104 lat band # 45 0.085 0.081 0.081 0.081 0.081 lat band # 46 0.081 0.077 0.078 0.080 0.083 lat band # 47 0.081 0.081 0.080 0.081 0.085 lat band # 48 0.081 0.082 0.079 0.083 0.084 lat band # 49 0.080 0.079 0.082 0.086 0.084 lat band # 50 0.081 0.083 0.085 0.086 0.087 lat band # 51 0.084 0.086 0.086 0.085 0.086 file SALB_monthly_199207.ascii has been written 8.0 Additional Derivable Parameters The parameters available from these files can be used to derive additional surface SW radiative parameters. SW cloud radiative forcing (SWCRF) at the surface can be derived from all-sky and clear-sky downward fluxes as SWCRF = FALL - FCLR Upward SW flux (FUP) can be derived from all-sky downward and absorbed surface fluxes as FUP = FALL - FABS Aerosol Radiative Forcing (ARF) at the surface under clear-sky condition can be derived from pristine-sky and clear-sky fluxes as ARF = FPRS - FCLR To compute these additional parameters, both quantities on the right hand side of the equations have to be available.