Model Change Bulletin

                            MCB#2                 6/11/90

                   DEGADIS 2.1 (dated 90162)



     This Model Change Bulletin documents changes made to the
DEGADIS 2.1 model FORTRAN source code since its installation on
the SCRAM bulletin board in January of 1990.  The new source code
will become available on the bulletin board on the date of this
notice, replacing the previous version dated 90012.

     This bulletin also announces the availability of "User's
Guide for the DEGADIS 2.1 Dense Gas Dispersion Model" through the
National Technical Information Service under the order number
PB90-213893.  It should be noted that the specific code changes
outlined in this Model Change Bulletin will not be included in
the code listing contained in that document.

     The specific changes incorporated into DEGADIS 2.1 date
90162 are as follows:

     1.  The program JETPLU has been modified so that maximum
concentration and plume centerline elevation as a function of
downwind distance are printed in the output.  Infinite values of
the Monin-Obukhov length are appropriately labeled (versus equal
to zero in the previous version).

     2.  The SURFACE program has been modified to allow for zero
windspeed simulations.

     3.  A coding error in ZBRENT has been corrected.

     4.  The PSS program has been extended to allow for lengthier
searches for the variable value of SZ before stopping.

     5.  The size of input arrays to the program DEGADISIN has
been increased from 30 to 42 by increasing the value of IGEN in
DEGADISIN.DEC from 30 to 42.

     6.  Initial and maximum integration step sizes have been
increased in the parameter file EXAMPLE.ER2.

     7.  Convergence criteria have been altered in the program
TPROP.

     8.  The computational method in the SERIES program has been
improved.

     9.  The convergence criteria in the ALPH program has been
changed.

     10. The initial specification of SY and SZ for transient
releases in the program SSSUP has been changed.

     11. The method of solving for b=0 in the programs PSSOUT and
PSSOUTSS has been improved.

     12. The output format for SRTOUT has been changed.
 
     As a reminder, the DEGADIS 2.1 model code available from
this bulletin board is a FORTRAN source code intended for
compilation and execution on a VAX computer using the VMS
operating system.  This code is not intended for use
on an IBM PC or clone.  A PC version is currently under
development and will be provided through this bulletin board when
it is cleared for public access.

     After the source code programs have been dearchived, the
file AAREADME.TXT should be consulted for information concerning
the transfer and compilation of that code on a VAX machine. 
Included with the source code are two example input files (EX1.IN
and EX2.IN) and their associated output files (EX1.OPT and
EX2.OPT), which may be used to test the code after compilation.

     This model will henceforth be identified by its name and a 
julian date, i.e.: DEGADIS 2.1 (90162). Future changes to this 
model will be identified by an updated julian date found on the 
first line of the model source code and followed by a reference 
to a SCRAM BBS Model Change Bulletin (MCB#n) which will explain 
the nature and contents of the changes. All Model Change 
Bulletins for this model will always be available for back 
reference on this BBS. In the future, notification of changes 
(MCBs) to this model will be made in the SCRAM ALERTS section 
of this BBS immediately following the LOGON procedure. 
 
      The source code for this model has been compiled and tested
on a VAX 8650 computer.  Watch SCRAM ALERTS for notification 
of new MCBs about DEGADIS 2.1.