Model Change Bulletin

                                    MCB#7                         06/04/99

                             ISCST3 (dated 99155)

    This Model Change Bulletin documents changes made to the Industrial
Source Complex Short Term (ISCST3) Dispersion Model (see Code Changes below).

[NOTE:  New ISC3 users are urged to read ISC3 MCB#1, Amendment #1 for
important information.  In addition, this change to the ISCST3 model does
not address the anomalous behavior of the dry deposition algorithm described
in MCB#2 and MCB#5.]

CODE CHANGES

    Changes from ISCST3 (dated 98356) include the following:

1.  A correction to an error in SUBROUTINE DEPCOR in applying a
    minimum value of 1 meter to the plume touchdown distance, XTD.

2.  A modification to the area source algorithm to correct anomalous
    results for very small area sources of about 1 meter width.

3.  A correction to the EVENTFIL output file option when the RECTABLE
    card is not included.

4.  A correction to SUBROUTINEs TERHGT and FLGHGT to prevent possible
    abnormal program termination when processing receptor elevations or
    flagpole heights for GRIDCART or GRIDPOLR receptors if there is an
    input error in defining the receptor grid.

5.  A correction to the re-start option (SAVEFILE/INITFILE keywords)
    for cases involving ANNUAL averages and/or post-1997 PM10 24-hour
    averages.

6.  Declaration of MODNAM as a local CHARACTER*12 variable, rather than
    in MODULE MAIN2.  MODULE MAIN2 has also been deleted.

7.  Modifications to optimize the ISCST3 model for air toxics applications,
    including the Sampled Chronological Input Model (SCIM) option,
    optimizations for the area source and dry depletion algorithms,
    inclusion of the gas dry deposition algorithm based on the draft
    GDISCDFT model, and the option to output results by season and
    hour of day (SEASONHR).  Details of the changes to ISCST3 associated
    with addition of this non-regulatory default TOXICS option are
    described in the Addendum to the ISC3 Model User's Guide (ISC3ADD1.WPD
    and ISC3ADD2.WPD).

8.  Modifications to date processing for Y2K compliance.  These
    modifications make use of the 4-digit year input on the ME SURFDATA
    card to identify the starting century and the starting 2-digit year for
    date windowing.  If a 2-digit year is input on the ME SURFDATA card,
    then a warning message is generated and a default window of 1950-2049
    is assumed.  All subsequent 2-digit years are converted to 4-digit years
    internally for date comparisons based on the SURFDATA input.  These
    modifications allow the ISCST3 model to be applied for all dates up
    through the year 2147 without modifying the format of the input
    meteorological data records (the limit of 2147 is due to the limit on
    the 10-digit full date as a 4-byte integer variable).  The output
    formats for the 8-digit variable, KURDAT, have also been changed
    to I8.8 to include leading zeros.


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                           *   IMPORTANT   *
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    This program will henceforth be identified by its name and a Julian date,
i.e.: ISCST3 (dated 99155).  Future changes to this model will be identified
by an updated Julian date found at the beginning of the model source code
and followed by a reference to a SCRAM Model Change Bulletin (MCB#n)
which will explain the nature and content of the changes.  All Model Change
Bulletins for this program will always be available for back reference on
this website.  In the future, notification of changes (MCBs) to this program
will be made in the SCRAM ALERTS section of this website.