Model Change Bulletin

                                  MCB#4                          8-15-96

                            MPRM (dated 96225)


     This Model Change Bulletin implements changes to the Meteorological
Processor for Regulatory Models (MPRM) associated with the August 1995
revision of Appendix W to 40 CFR Part 51.  The enhancements include the
addition of algorithms to calculate boundary layer parameters which are used
in the revised Industrial Source Complex model (ISC) to estimate deposition
velocity and plume depletion.  Other enhancements include processing of
hourly precipitation data (for use in wet deposition calculations),
processing of National Weather Service (NWS) surface data which are now
available on CD-ROM, and coding to implement the Solar Radiation Delta-T
(SRDT) method of stability classification.

     These changes constitute MPRM (dated 96225).  With this bulletin the
source code and executables for MPRM (dated 96225) are being made available
for downloading from the 'Model Related Programs' area of SCRAM.  MPRM
(dated 96225) replaces MPRM (dated 93140) and the Beta version [MPBV02
(dated 95261)].  These old versions are obsolete and, with this bulletin,
will no longer be available on SCRAM.  All copies of such should be
discarded.

     Details regarding the revised MPRM can be found in the revised MPRM
User's Guide (EPA-454/B-96-002).  The user's guide is available for
downloading from the 'Model Related Programs' area on the main SCRAM menu
under User's Guides.

     The enhancements are summarized in the following:

1.   Algorithms for Boundary Layer Parameters - Estimates of two boundary
     layer parameters (the friction velocity and Monin-Obukhov length) are
     required in the revised ISC short-term model (ISCST3) for use in
     deposition and plume depletion calculations.  The friction velocity
     (u*) is a measure of the stress due to wind shear at the earth's
     surface.  The Monin-Obukhov length (L) is a stability parameter that
     relates the friction velocity to the transfer of heat.  The
     computations require user specified surface characteristics including
     albedo, Bowen ratio, and roughness length.  The surface characteristics
     are allowed to vary with time of year and/or wind direction (sector).

2.   Processing of Hourly Precipitation Data - Hourly precipitation data
     are required in ISCST3 for use in estimating wet deposition.  To support
     wet deposition estimates, MPRM has been enhanced to accommodate
     processing of TD-3240 precipitation data files available from the
     National Climatic Data Center (NCDC).

3.   Processing of CD-ROM Surface Data - NCDC now provides solar and surface
     meteorological data (including hourly precipitation) on CD-ROM.  Data
     for first order stations for 1961 - 1990 are available on a set of three
     CD-ROMs, collectively referred to as the SAMSON data.  MPRM has been
     enhanced to accommodate processing of SAMSON data.

4.   Estimating Stability Using the SRDT Method - The Solar Radiation
     Delta-T (SRDT) method of stability classification is based on site
     specific measurements of wind speed in combination with solar radiation
     during the day, and low-level vertical temperature difference at night.
     The algorithm implemented in MPRM (dated 96225) is identical to that
     implemented and tested in MPBV02 (dated 95261).


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                           *   IMPORTANT   *
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    This program will henceforth be identified by its name and a Julian date,
i.e.: MPRM (dated 96225).  Future changes to this program will be identified
by an updated Julian date found at the beginning of the program source code
and followed by a reference to a SCRAM BBS 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 BBS.  In the future, notification of changes (MCBs) to this program will
be made in the SCRAM ALERTS section of this BBS immediately following the
LOGON procedure.