Model Change Bulletin
              
                                    MCB#3                         12/29/97

                             ISCST3 (dated 97363)


    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 does not include a revised EVENT processor (ISCEV3).]


CODE CHANGES

    Changes from ISCST3 (dated 96113) include the following:

1.  Correction to the vertical virtual distance calculation for rural
    conditions, which can affect volume and building downwash sources;

2.  Correction for area sources when CONC, DDEP, and WDEP are calculated;

3.  Correction to SUBROUTINE RSINIT;

4.  Correction to the output units label for ANNUAL average deposition
    fluxes;

5.  Correction for cases when the flagpole receptor height is above the
    mixing height;

6.  Correction to SUBROUTINE DEPCOR to ensure unlimited mixing for stable
    conditions;

7.  Change of the deposition reference height, ZRDEP, to 1.0m instead
    of 20.*Z0M;

8.  Correction to the interpolation routine used in SUBROUTINE TGQA; and

9.  Minor cosmetic changes including corrections to format statements.


Sensitivity tests performed on the correction to the vertical virtual
distance for rural conditions showed little or no affect on design
concentrations for a range of typical source characteristics, and
meteorological regimes.


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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 97363).  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 contents 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.