OPAC installation and usage

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OPAC installation and usage

The OPAC package

This is Version 3.1a of OPAC, as published in 1998.

We don't get funding for this project any longer and thus we can't spend much time for it. But we appreciate any hints about problems with the data set or suggestions for its improvement, and we will try to discuss and include them in future versions. Please use this forum for your hints.

OPAC consists of ASCII files, which contain the optical properties of cloud and aerosol components, and of a FORTRAN program, which allows to handle the data. The FORTRAN program was originally (i.e. in 1998) tested to compile and run under DOS (Microsoft Fortran 5.0), Linux (GNU f2c converter), DEC Ultrix, HP Unix, and SunOS.

The whole package requires about 3.5 MB storage capacity.


To install OPAC, please extract the archive in an empty directory:

> gzip -d opac31a.tar.gz
> tar -xvf opac31a.tar

This will create 2 subdirectories and copy all files in their appropriate places. The tar and gzip programs are also available for DOS.

If you did already install the Global Aerosol Data Set (GADS), you should install OPAC in the same directory, since GADS and OPAC use the same set of optical data of aerosol components, which are stored in the subdirectory optdat.

Now the FORTRAN program has to be compiled. On most UNIX computers, this requires something like:

> f77 opac.f -o opac

In this case, opac will be the name of the executable file. Some compilers give warning errors, which may be ignored. A DOS and a WINDOWS executable can be downloaded here.

If you want to use a DOS computer, you must comment out lines 505-507 instead of 501-503 in opac.f. The "\" character is not understood by all compilers.

The following files belong to OPAC:

  • The optical properties of the clouds and of the 10 aerosol components, for up to 8 relative humidities and 61 wavelengths are stored in the subdirectory optdat. Each cloud or aerosol component has up to 8 files (for the humidity classes), each containing data for all 61 wavelengths. The filename consists of a 4 letter approximation for the cloud or the aerosol component, combined with the relative humidity, for which the optical properties have been calculated. For clouds only 1 file exists, which is attributed to 0% humidity, indicating that there is no dependence of size distribution with relative humidity taken into account.
    ~ 0% 50% 70% 80% 90% 95% 98% 99%
    insoluble inso00 - - - - - - -
    watersoluble waso00 waso50 waso70 waso80 waso90 waso95 waso98 waso99
    soot soot00 - - - - - - -
    sea salt(acc. mode) ssam00 ssam50 ssam70 ssam80 ssam90 ssam95 ssam98 ssam99
    sea salt(coa. mode) sscm00 sscm50 sscm70 sscm80 sscm90 sscm95 sscm98 sscm99
    mineral (nuc. mode) minm00 - - - - - - -
    mineral (acc. mode) miam00 - - - - - - -
    mineral (coa. mode) micm00 - - - - - - -
    mineral (transported) mitr00 - - - - - - -
    sulfate droplets suso00 suso50 suso70 suso80 suso90 suso95 suso98 suso99
    . . . . . . . . .
    stratus (continental) stco00 - - - - - - -
    stratus (maritime) stma00 - - - - - - -
    cumulus (cont., clean) cucc00 - - - - - - -
    cumulus (cont., poll.) cucp00 - - - - - - -
    cumulus (maritime) cuma00 - - - - - - -
    fog fogr00 - - - - - - -
    cirrus 1: -25°C cir100 - - - - - - -
    cirrus 2: -50°C cir200 - - - - - - -
    cirrus 3: -50°C
    (+ small particles)
    cir300 - - - - - - -

  • All other files are stored in the subdirectory OPAC31. Here you can find the FORTRAN program and additional configuration and data files:
    • opac.f is the FORTRAN program. It is used to calculate data which are not directly stored in the data base.
    • opac.cfg contains all the microphysical information about the aerosol and cloud size distributions, the aerosol height profiles, the composition of aerosol types.
    • extback.dat contains wavelength dependent extinction coefficients of the background aerosols, i.e. the free tropospheric aerosol, the stratospheric aerosol and the mineral aerosol in the desert dust layer. These values are needed for calculating optical depths.
    • solar.dat contains information about the extraterrestrial solar flux. This is needed for calculations of spectrally weighted broadband extincion properties in the solar spectral range.
    • ter.dat contains information about the terrestrial emission between 8 µm and 15 µm for a temperature of 300 K. This is needed for calculations of spectrally weighted broadband extincion properties in the terrestrial spectral range.
    • wel.dat contains wavelength information for the calculation of spectrally weighted extinction properties.

    There are 2 subdirectories in directory OPAC31:

    • input: Each input file for opac.f, which contains data and parameters to be extracted from OPAC must be stored in a file in this directory. The program prompts you for the filename and automatically appends the extension ".inp". As an example, the file opac.inp is provided.
    • result: Here the results of your inquiry are stored. The given filename is used with the extension ".out". As an example, the file opac.out belonging to opac.inp is provided.

    Using the program

    The purpose of the program is to mix optical properties of single cloud or aerosol components (stored for 1 particle/cm^3) to optical properties of clouds or aerosol types, which may consist of several components. It is also possible to calculate optical properties which are not stored in the data base. These are for instance the optical depth, the extinction ratio (extinction coefficient divided by mass), or quantities which are integrated over the solar or terrestrial wavelength range.

    Before starting the program, you have to edit an input file in order to define, which information you want to extract and calculate from the data base. Since the program prompts you for the name of the input file, you can use copies of the example and default input file opac.inp.

    The program is started by typing opac in the subdirectory opac31, if you used the compiler command shown above.

    The results are stored in the subdirectory result in files, whose names consist of the input file name, but with the extension .inp replaced by .out.

    If you have the feeling, that the instructions given here, together with the explanations in the OPAC paper (Hess et al., 1998) are not sufficient, please ask your questions in this forum.