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. ***************** * IMPORTANT * ***************** 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.