                               
                        Model Change Bulletin

                               MCB#3                       12/10/2012

                        AERMET (dated 12345)

This Model Change Bulletin (MCB) documents changes made to the AERMET 
Meteorological Preprocessor for the AERMOD Dispersion Model.  A brief 
description of the changes is provided below.  Additional details are 
also available through comments embedded in the Fortran source code. 
Changes to the user instructions associated with this update are 
documented in a separate AERMET User's Guide Addendum.


This revised version of AERMET (dated 12345) includes the following
modifications relative to the previous version (dated 11059):

                                                                        
-- Bug Fixes:                                                           

   1.  Modified subroutine DOCLDS to correct for errors that 
       result when blank spaces occur between the cloud cover 
       and ceiling height fields for HUSWO surface data. Also 
       modified DOCLDS to no longer accept invalid ASOS cloud 
       cover codes for HUSWO surface data. These bug fixes 
       should not affect results for HUSWO surface data that
       were extracted from the HUSWO CD, but could affect 
       results significantly for applications using surface
       data that were reformatted to the HUSWO format from
       another data format.

   2.  Modified subroutine CBLHT to correct an error in the
       calculation of the convective mixing height. Previous
       versions of AERMET may have underestimated convective
       mixing heights, and in turn the convective velocity
       scale (w*), due to this error. The magnitude of the
       errors would tend to be larger for cases where the
       vertical temperature profile based on the upper air
       sounding was based on fewer sounding levels. However,
       due to the widespread nature of these convective mixing
       height errors, AERMOD modeling results are likely to
       be affected to some degree by this AERMET bug fix in 
       most cases.
       
       The magnitude and direction of changes in AERMOD model
       results due to this convective mixing height bug fix
       will vary depending on the resolution of the upper
       air data and the characteristics of the sources and
       terrain included in the AERMOD model application. Also,
       as noted in Section 3.2 of the "AERMOD Implementation 
       Guide," upper air data input to AERMET should be based
       on "all levels" or "mandatory and significant levels" 
       to ensure adequate resolution of the vertical profile;
       use of upper air data based on "mandatory levels only"
       is not acceptable for AERMOD modeling applications.

   3.  Modified subroutines CBLHT, MPPBL, MPMET, and SETUP
       to check for ONSITE mixing heights (OSMIX) in the
       determination of data completeness, and adjusted
       warning messages to account for possible presence
       of both ONSITE mixing heights and UPPERAIR data.


-- Enhancements:

   1.  Added a new THRESH_1MIN keyword to Stage 3 processing. 
       This optional keyword allows the user to specify a threshold 
       wind speed below which winds reported in the 1-minute ASOS
       data processed through AERMINUTE, if in use, are considered 
       calm. There is no default value; however, a warning message
       will be generated if the user-specified threshold is greater
       than 0.5 m/s, and a fatal error message will be generated 
       if the user-specified threshold is less than zero or greater
       than 1.0.  

       This new keyword also required that the length of the 
       KEYWRD variable be increased from 10 to 12 characters, 
       resulting in modifications to several subroutines.

   2.  Incorporated a new "BETA" option to adjust u* (ustar) 
       for low wind speed stable conditions, based on Qian, W., 
       and A. Venkatram, 2011: Performance of Steady-State 
       Dispersion Models Under Low Wind-Speed Conditions. 
       Boundary-Layer Meteorology, 138, 475-491. The new option
       is selected by including the METHOD STABLEBL ADJ_U* 
       keyword on the METPREP pathway in the Stage 3 input file.

       The ADJ_U* "BETA" option is considered to be a non-Default 
       option and is therefore subject to the alternative model 
       provisions in Section 3.2 of Appendix W (40 CFR Part 51). 
       Users should coordinate with the appropriate reviewing 
       authority regarding the procedures and requirements for 
       approval of this BETA option for regulatory modeling 
       applications.  Use of this option also requires the user 
       to include the BETA option on the CO MODELOPT keyword in 
       the AERMOD input file.

   3.  Arrays for storing upper air soundings were increased to 
       accommodate up to 48 soundings, including the current
       day and the previous day.


-- Miscellaneous:

   1.  The value used to adjust ASOS wind speeds to account for 
       bias due to wind speeds being truncated to whole knots was 
       modified to include three significant digits (from 0.26 m/s 
       to 0.257 m/s, based on 0.5 kt). This modification avoids 
       potential for mis-characterization of calm vs. non-calm 
       due to precision issues associated with the truncation 
       adjustment under the new THRESH_1MIN option.

   2.  Modified subroutine GETFSL to issue a non-fatal warning 
       instead of a fatal error message when the UA station ID
       specified on the UA LOCATION keyword does not match the
       UA station ID in the data file. This change will accommodate 
       substitutions for missing UA soundings using data from other 
       representative UA stations, and will document when such 
       substitutions were made in the Stage 1 report file. 
       Since all convective hours will be missing on days when the
       UA sounding is missing, this will allow users to minimize 
       the number of missing hours in the AERMET-processed surface 
       file due to missing UA soundings, while maintaining a record 
       of when such substitutions were made and identifying which 
       alternative sites were used.

   3.  Modified subroutine RDHUSW for processing HUSWO surface 
       data to change the "no records extracted" warning message 
       to a fatal error.

   4.  Modified subroutines EQ_CCVR and INCRAD to remove a trailing
       period within the single quotes in the INCLUDE 'WORK1.INC' 
       statements. 


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                       *   IMPORTANT   *
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This program will henceforth be identified by its name and a Julian date,
i.e.: AERMET (dated 12345).  Future changes to AERMET will be identified
by an updated Julian date found at the beginning of the 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.
                                                                           