PROCESS_ANALYSIS_NOTES  5 Aug 2004


The following describes procedures for conducting process analyses with the CMAQ 
modeling system in a stand alone mode.  Process analysis is a diagnostic tool 
that can be used by the modeling analyst to quantify contributions of individual 
science processes to model predicted concentrations. Such information is useful 
for understanding a model's predictions and for determining why predictions 
change when the model configuration is changed or when model inputs are changed. 
Technical details of the CMAQ implementation of process analysis are contained 
in Chapter 16 of the "Science Algorithms of the EPA Models-3 Community 
Multiscale Air Quality (CMAQ) Modeling System (EPA-600/R-99/030), and will not 
be repeated here.  The focus here is on the operational steps necessary to 
invoke process analysis in the CMAQ system.

The CMAQ run scripts included with this release are set-up such that process
analysis is de-activated.  This is accomplished by including three "noop"
include files that effectively turn off process analysis - PA_CTL.EXT,
PA_DAT.EXT and PA_CMN.EXT.  Whenever process analysis is to be omitted, these
three "noop" files should be used when the CMAQ chemical transport model (CCTM)
is compiled.

To activate Process Analysis, the three "noop" files must be replaced with three
files that define the information to be collected during the model simulation.
These files are generated by running the Process Analysis Control Program
(PACP), for which bldit and run scripts are provided with this release.  The
steps to invoke process analysis follow.

  1.  Create an ASCII text file containing process analysis commands (see
      Chapter 16 of the aforementioned "science" document for command rules and
      syntax).

  2.  Build the PACP using the bldit script.  Note that the CVSROOT 
      directory should point to the PROCAN subdirectory of the source archive 
      (e.g., in the accompanying bldit script, the variable "Project" is set to 
      $M3MODEL/PROCAN). The only change to the release script that may be 
      required involves the chemical mechanism.  The script variable "Mechanism" 
      must be set to the chemical mechanism that will be used in the CCTM.

  3.  Run the PACP using the run script.  The input file to be used can be
      defined using the environment variable PACP_INFILE. (If this environment
      variable is not set, the PACP will look for an input file named "pa.inp"
      in the run directory.)  The output of the PACP consists of four ASCII
      files: the aforementioned three include files (PA_CTL.EXT, PA_CMN.EXT, and
      PA_DAT.EXT), and a PA_REPORT file that is included for informational
      purposes.  All four output files will be placed in the run directory.

  4.  Use the three include files generated by the PACP program in lieu of 
      the "noop" files when the CCTM is built (i.e., change the "ICL_PA" 
      variable in the CCTM bldit script to point to the path of the include 
      files generated by the PACP).  The process analysis output files generated 
      by the CCTM will be included with the other CCTM output files in the 
      OUTDIR specied in the run script for the CCTM.  See special note b) below 
      regarding setting the output domain before running the CCTM.


Special notes:

  a)  When invoking process analysis, be sure to use the same chemical
      mechanism when building the PACP and the CCTM.  At present no consistency
      check is performed, and the use of inconsistent mechanisms will produce
      erroneous results.

  b)  As described in the "Science" document, the domain for process
      analysis can be set smaller than the CCTM computational domain to reduce
      computer resources.  The "Science" document indicates that the process
      analysis output domain is set using the OUTPUT_DOMAIN command in the PACP
      input file.  That is no longer the case.  The process analysis domain is
      now set in the CMAQ run script via the environment variables PA_BCOL_ECOL,
      PA_BROW_EROW, and PA_BLEV_ELEV.  When process analysis is invoked, these
      variables MUST be un-commented and set appropriately.  The PACP is now
      programmed to terminate with an error message if the OUTPUT_DOMAIN command
      is included in the PACP input file.

  c)  An example PACP input file and corresponding output files are included
      in the "data" directory of this release, but these files have not been
      used in the example CCTM run.