SRB_REL3.0_QCLW_3HRLY - GEWEX Quality-Check Longwave 3-Hourly README File
1.0 Introduction
This README file provides information on the SRB_REL3.0_QCLW_3HRLY data set. The
data set contains global fields of instantaneous 3-hourly values of three
longwave (LW) surface radiative parameters derived with the Quality-Check LW
(QCLW) algorithm of the NASA World Climate Research Programme /Global Energy and
Water-Cycle Experiment (WCRP/GEWEX) Surface Radiation Budget (SRB) Project.
If users have any 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
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
There are a total of three parameters in these files as follows:
1. Surface Downward Longwave Flux (DLF), 
2. Surface Net Longwave Flux (NLF), and
3. Surface Longwave Cloud Radiative Forcing (LWCRF).
These parameters were derived on a 3-hourly temporal resolution (i.e., a global
instantaneous gridded field every 3 hours), namely, at UT hours 00, 03, 06, 09,
12 15, 18, and 21 for every day of the month.  The current version of the data
sets is designated as Release 3.0.  It covers a period of 23 years from July
1983 to June 2006.
Detailed description of the algorithm used in deriving these parameters can be
found in:
Gupta et al. (1992) - J. Appl. Meteor., 31, 1361-1367.
Gupta (1989)        - J. Climate, 2, 305-320.
Wilber et al. (1999) - NASA/TP-1999-209362, 35 pp. (available on the web from
http://techreports.larc.nasa.gov/ltrs/ltrs.html)
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/
2.1.2. 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 became 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 longwave radiation is lower in the gap, creating an
appearance of a flux discontinuity.  For 3-hourly fluxes a discontinuity of
magnitude less than 5 W/m**2 may appear in the Indian Ocean depending upon the
meteorological conditions.
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)
Surface emissivities were taken from a map developed at NASA LaRC (Wilber et al.
1999; see reference above).
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
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
These files contain an entire month of 3-hourly 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 binary data and are named
according to the following convention:
srb_rel3.0_qclw_3hrly_yyyymm.binary, where
srb          Project name, Surface Radiation Budget
rel3.0       Release number for these data (Release 3.0)
qclw         Name of the algorithm, Quality-Check Longwave
3hrly        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 values of the following three
parameters for the whole month on the nested grid.  Each file has up to 744
records; 3 records every 3 hours during the month; one for each parameter in the
order they are listed below.  The first 3 records are for hour 00 of day 1, the
next 3 for hour 03, and so on.
Name:  Surface Downward LW Flux (DLF)
Units:  Watts per square meter
Type:  Real
Range:  50 to 750
Fill Values:  -999.0
Scale Factor:  None
Name:  Surface Net LW Flux (NLF)
Units:  Watts per square meter
Type:  Real
Range:  -250 to 50
Fill Values:  -999.0
Scale Factor:  None
Name:  Surface LW Cloud Radiative Forcing (LWCRF)
Units:  Watts per square meter
Type:  Real
Range:  0 to 150
Fill Values:  -999.0
Scale Factor:  None
5.0 Sample Read Software Description
Sample read software written in Fortran-90, read_srb_rel3_qclw_3hrly.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_qclw_3hrly.nml).  The input files are direct-access
binary on the nested (44016 cell) grid.  The software reads one or more of the 3
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.
   DLF=.true.
   NLF=.true.
   LWCRF=.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 code is that it provides one file for each parameter containing complete
global fields for all 3-hourly times of the month.  From these files the user
should be easily able to extract a field for any time of the month and also, the
values for any box or lat-lon region.
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_qclw_3hrly read_srb_rel3_qclw_3hrly.f90  <return>
The providers used a IBM XL 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_qclw_3hrly  <return>
7.0 Sample Output
When the is code run, the following information appears on the screen:
The three 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) for hour 06 of day 14 of the
month.  Values for only a small lat-lon box for a single time are printed to the
screen.
 *****************************************************************
 *                                                               *
 *                                                               *
 * Data Set srb_rel3.0_qclw_3hrly 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_rel3.0_qclw_3hrly_199207.binary input file is opened
Variable DLF_ Hour = 06  Day = 14
lon # =            100       101       102       103       104
lat band #  45   311.622   305.943   305.943   317.618   317.618
lat band #  46   312.344   311.539   324.053   319.517   329.898
lat band #  47   358.951   358.556   344.426   327.131   315.679
lat band #  48   361.034   340.000   314.358   314.292   313.964
lat band #  49   328.863   316.699   320.614   324.151   323.911
lat band #  50   326.036   326.551   330.861   326.143   335.075
lat band #  51   358.127   342.728   336.332   342.477   361.960
/DLF_3hrly_199207.ascii has been written
Variable NLF_ Hour = 06  Day = 14
lon # =            100       101       102       103       104
lat band #  45   -44.071   -50.242   -50.242   -38.993   -38.993
lat band #  46   -47.750   -48.583   -36.356   -40.913   -30.234
lat band #  47    -5.549    -5.688   -19.560   -36.414   -47.037
lat band #  48    -6.018   -26.484   -51.523   -51.021   -50.494
lat band #  49   -39.396   -51.198   -46.882   -42.701   -42.221
lat band #  50   -43.948   -43.515   -38.963   -43.095   -33.820
lat band #  51   -14.415   -30.151   -36.553   -30.292   -10.991
/NLF_3hrly_199207.ascii has been written
Variable LWCRF_ Hour = 06  Day = 14
lon # =            100       101       102       103       104
lat band #  45    34.517    27.241    27.241    40.804    40.804
lat band #  46    30.967    32.041    46.245    42.814    53.624
lat band #  47    78.711    79.916    66.145    48.841    39.730
lat band #  48    80.827    59.684    35.880    36.242    36.817
lat band #  49    48.551    36.421    40.709    45.247    45.296
lat band #  50    44.880    44.956    50.000    46.464    56.515
lat band #  51    76.304    61.846    56.578    63.739    83.820
/LWCRF_3hrly_199207.ascii has been written
8.0 Additional Derivable Parameters
It is important to keep in mind that NLF is computed as
NLF = DLF - Upward LW Flux (ULF)
and is, therefore, generally a negative number.  Also, the three parameters
provided in these files can be used to compute two additional surface LW
parameters, if needed.
ULF (Upward Longwave Flux) can be computed as
ULF = DLF - NLF
Clear-sky DLF (CSDLF) can be computed as
CSDLF = DLF - LWCRF
To compute these additional parameters, both quantities on the right hand side
of the equations have to be available.