Model Change Bulletin MCB#1 12/07/2006 AERMET (dated 06341) This Model Change Bulletin 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 imbedded in the Fortran source code; the latter are cross referenced in an annotated list of changes which accompanies the 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 06341) includes the following modifications relative to the previous version (dated 04300): Bug Fixes: 1. Corrected several problems associated with the extraction and processing of Integrated Surface Hourly Data (a.k.a., ISHD, ISH, ISD, TD-3505), including: a) Modified the procedure for selecting which record to process for hours with multiple records, including treatment of "special" observation records - AERMET now uses the last record up to and including the hour, but will only use a "special" observation (types FM-15 or SAOSP) if the only observation available for the hour is a "special"; b) Corrected code for processing of sky cover data fields; c) Corrected initialization of "additional" character variable to avoid data fields from previous hours being used; d) Added code for identifying "variable" winds with valid wind speed but missing wind direction (formerly flagged as calms); e) Modified to include additional observation types as acceptable for processing to avoid skipping valid data; f) Corrected problem that would cause the observation hour to be incremented prematurely, resulting in valid data being overwritten in some cases; g) Corrected the code for estimating station pressure and sea-level pressure when one or the other is missing; h) Added code to check for "missing" station elevation (9999) for files that have been expanded to include location fields using the National Climatic Data Center (NCDC) utility program. If a missing elevation is found, then AERMET will use the assigned value based on the optional elevation field on the LOCATION card, if available. If the LOCATION elevation field is omitted, the assigned value is defaulted to 100m . See Items 2 and 3a under "Enhancements" below for related information. i) Modified subroutines RDISHD and ISHWX for processing of ISHD surface format "present weather" data codes to determine precipitation type code (liquid or frozen). 2. Modified the upper and lower bounds for the surface level pressure in subroutine GETFSL to avoid skipping valid upper air soundings for stations located at high or low elevations. 3. Modified subroutine RDHUSW to correct the missing data codes for wind speed and direction for HUSWO surface data. 4. Modified subroutine D3280L to assign the correct missing data code for missing wind direction, and to also process variable wind code with valid wind speed but missing wind direction. 5. Modified subroutines MPPBL and NR_ANG to correct problems with calculation of critical solar angle (ACRIT), including modifications to handling of missing data in the calculation of ACRIT. 6. Revised format statement in subroutine REALQA to avoid overflowing the message field. 7. Revised subroutine SMTHZI to include a limit on the exponential argument to avoid a runtime underflow and to use the correct missing data code for ustar. 8. Revised subroutine RDSAMS to correct the format statement for a character variable. Enhancements: 1. Modified code to use a single AERMET.EXE executable file, replacing the separate STAGE1N2 and STAGE3 executables. Note this only affects the number of executables; users must still run each stage separately. The new AERMET executable is also hardcoded to read the input data from an 'AERMET.INP' file, but the format of the input files has not changed, other than the enhancement noted in Item 2 below. 2. The code for processing the 'LOCATION' input image has been revised to allow users the option of including station elevation in the last field of the input image. This addresses potential problems related to the estimation of surface pressure from sea-level pressure when processing surface data in the ISHD format. The optional user-specified elevation from the LOCATION card is currently used only to substitute for missing elevation values in the ISHD data format for the SURFACE pathway. Optional elevation values input for other surface data formats or for the UPPERAIR, ONSITE and METPREP pathways are currenlty ignored. 3. Revised code for extracting and processing surface data in the ISHD format as follows: a) The format of every record is checked to determine whether the record includes station location and elevation. This will allow users to process 'mixed-format' files, such as would be created by appending records in one format to a data file comprised of records in the other format; b) Overwritten hourly records are saved by writing them to the error/message file; and c) Added a counter to track the number of hourly records with a variable wind direction flag. Miscellaneous: 1. Modified several subroutines to impose a lower limit on the value of surface roughness length of 0.001 meters, for consistency with the AERMOD dispersion model. 2. The optional user-specified time window for extracting and processing ISHD surface data has been removed, and the default extraction window has been increased from 10 minutes to 30 minutes preceding the hour. 3. Added code to subroutines SUBST and MPPBL to trap on problem with determining the wind direction sector for surface characteristics to avoid compiler runtime errors. Such a condition should not occur, but could indicate a problem with data formatting or with the AERMET code. ***************** * IMPORTANT * ***************** This program will henceforth be identified by its name and a Julian date, i.e.: AERMET (dated 06341). 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.