SRB_REL3.0_QCLW_DAILY - GEWEX Quality-Check Longwave Daily-Average Data set
README File
1.0 Introduction
This README file provides information on the SRB_REL3.0_QCLW_DAILY data set. The
data set contains daily average global fields 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 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
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 originally on a 3-hourly temporal resolution
(i.e., a global instantaneous gridded field every 3 hours).  The 3-hourly values
are averaged into the daily values given in these files.  The current version of
the data sets is identified as Release 3.0.
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 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 longwave radiation is lower in the gap, creating an
appearance of a flux discontinuity.  For Daily averaged fluxes a discontinuity
of magnitude less than 5 W/m**2 for surface fluxes may appear in the Indian
Ocean gap region.
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
Each data file contains an entire month of daily 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 contain binary data and are named according
to the following convention:
srb_rel3.0_qclw_daily_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
daily        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 daily averages of the following three
parameters for the whole month on the nested grid.  Each file has up to 93
records; 3 records for each day of the month; one for each parameter in the
order they are listed below.  The first 3 records are for day 1, the next 3 for
day 2, and so on.
Name:  Surface Downward LW Flux (DLF) 
Units:  Watts per square meter 
Type:  Real
Range:  50 to 650 
Fill Values:  -999.0 
Scale Factor:  None
Name:  Surface Net LW Flux (NLF) 
Units:  Watts per square meter 
Type:  Real
Range:  -180 to 20 
Fill Values:  -999.0 
Scale Factor:  None
Name:  Surface LW Cloud Radiative Forcing (LWCRF) 
Units:  Watts per square meter
Type:  Real Range:  0 to 120 
Fill Values:  -999.0 
Scale Factor:  None
5.0 Sample Read Software Description
Sample read software written in Fortran-90, read_srb_rel3_qclw_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_qclw_daily.nml).  The input files are direct-access
binary on the nested (44016 box) 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 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_qclw_daily read_srb_rel3_qclw_daily.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_daily  <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 day 14 of the month. 
Values for only a small lat-lon box for a single day are printed to the screen.
 *****************************************************************
 *                                                               *
 *                                                               *
 * Data Set srb_rel3.0_qclw_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: larc@eos.nasa.gov                                     *
 * Phone: (757)864-8656                                          *
 * FAX: (757)864-8807                                            *
 *                                                               *
 *****************************************************************
 /srb_rel3.0_qclw_daily_199207.binary input file is opened
 Variable DLF_Day =  14
lon # =            100       101       102       103       104
lat band #  45   306.194   310.353   310.353   311.753   311.753
lat band #  46   304.386   309.201   312.859   319.265   316.202
lat band #  47   320.493   326.519   319.368   321.044   317.952
lat band #  48   323.037   321.123   311.914   318.752   323.763
lat band #  49   325.820   324.909   326.430   334.524   328.781
lat band #  50   333.923   335.437   336.292   337.778   322.462
lat band #  51   343.333   333.326   330.843   336.362   337.300
 file DLF_daily_199207.ascii has been written
 Variable NLF_Day =  14
lon # =            100       101       102       103       104
lat band #  45   -49.502   -45.924   -45.924   -44.844   -44.844
lat band #  46   -55.695   -50.957   -47.502   -41.214   -43.841
lat band #  47   -43.719   -37.492   -44.448   -42.502   -44.831
lat band #  48   -43.737   -45.258   -54.014   -46.667   -40.841
lat band #  49   -42.490   -43.141   -41.195   -32.495   -37.461
lat band #  50   -36.212   -34.791   -33.661   -31.644   -46.389
lat band #  51   -29.147   -39.544   -42.071   -36.431   -35.501
 file NLF_daily_199207.ascii has been written
 Variable LWCRF_Day =  14
lon # =            100       101       102       103       104
lat band #  45    38.264    37.224    37.224    36.374    36.374
lat band #  46    29.600    32.993    35.739    41.958    39.272
lat band #  47    42.173    47.430    40.146    42.603    40.268
lat band #  48    42.073    39.866    31.368    39.003    44.283
lat band #  49    42.365    41.885    43.861    52.401    46.853
lat band #  50    48.326    50.131    51.563    53.091    38.576
lat band #  51    56.089    46.305    44.210    50.404    52.721
 file LWCRF_daily_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 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.