The program ICON prepares chemical initial conditions (ICs) for the CMAQ Chemistry Transport Model (CCTM). ICON will generate an output file with chemical concentrations for all grid cells in the modeling domain. Depending on user specified options and/or input datasets, the ICs generated by ICON can be time dependent, time independent, and either spatially uniform or variable across the modeling domain. If deriving ICs from the ASCII vertical profiles, ICON creates spatially uniform, time independent ICs. From concentration (CONC) files, ICON extracts spatially varying ICs, either on the same grid cell resolution (windowed modeling domain), or for a finer grid resolution modeling domain (nested modeling domain). ICs generated from CONC files are time dependent if the input CONC file is time stepped, or time independent if the CONC file time step is zero.
There are two distinct modes of operation for ICON. When running ICON, the user must specify whether to generate ICs from: (1) an existing CONC file (regrid); or (2) an ASCII file of vertical profiles (profile).
The User's Guide contains a tutorial on how to use ICON to create initial conditions from seasonal or daily average hemispheric CMAQ output files distributed through the CMAS data warehouse.
CMAQ can also use initial conditions derived from global chemistry models (GCMs). While ICON does not directly support processing of datasets from GCMs (in their native formats), users could develop their own custom codes to transform their GCM datasets into I/O API format, which would then allow these datasets to be input into ICON to generate ICs for the CCTM.
Table 1. Runtime Environment Variables
| Variable Name | Example in Runscript | Description |
|---|---|---|
| VRSN | v53 | Identifies version for the ICON run. Its value should be consistent between BCON build and run scripts for an individual application. |
| APPL | SE53BENCH | Identifies the intent of the ICON run such as the model domain and chemical mechanism used. Value is the user's preference. |
| ICTYPE | regrid, profile | Specifies which IC type to generate. |
| EXEC | ICON_${VRSN}.exe | Executable to use for the ICON run. |
| GRIDDESC | $CMAQ_HOME/scripts/GRIDDESC1 | Grid description file for setting the horizontal grid definition for the target domain. |
| GRID_NAME | SE53BENCH | Name of the grid definition contained in the GRIDDESC file that specifies the horizontal grid for the target domain. |
| OUTDIR | $CMAQ_HOME/data/icon | Output data directory |
| SDATE | 0 | Julian start date for extracting initial conditions from a CCTM CONC file. If SDATE is not set, it will be set automatically from the MET_CRO_3D_FIN file. |
| STIME | 0 | Start time for extracting initial conditions from a CCTM CONC file. If STIME is not set, it will be set automatically from the MET_CRO_3D_FIN file. |
| IOAPI_ISPH | 20 | I/O API setting for spheroid type. See I/O API documentation for setsphere for more information. |
| IOAPI_OFFSET_64 | YES | I/O API setting for large time-step records. If your output time step is going to produce data that are >2GB per time step, then this needs to be set to YES. |
Table 2. ICON input files for ICTYPE equals "regrid"
| File Name | Format | Description |
|---|---|---|
| GRIDDESC | ASCII | Horizontal grid description file for defining the model grid; this file is output by MCIP or can be created by the user |
| CTM_CONC_1 | IOAPI/GRDDED3 | Name and location of the CMAQ concentration file from which to derive initial conditions; this file is output from CCTM |
| MET_CRO_3D_CRS | IOAPI/GRDDED3 | Name and location of the coarse-grid MET_CRO_3D file that is required for creating the vertical grid structure if this structure changes between nested simulations; this file is output by MCIP |
| MET_CRO_3D_FIN | IOAPI/GRDDED3 | Name and location of the fine grid MET_CRO_3D file that is required if the vertical grid structure changes between nested simulations; this file is output by MCIP |
Table 3. ICON input files for ICTYPE equals "profile"
| File Name | Format | Description |
|---|---|---|
| GRIDDESC | ASCII | Horizontal grid description file for defining the model grid for the target domain; this file is output by MCIP or can be created by the user |
| IC_PROFILE | ASCII | Vertical chemical profiles from which to derive initial conditions; this file can created by the user |
| MET_CRO_3D_FIN | IOAPI/BNDARY3 | Name and location of the fine-grid (or target modeling domain) MET_CRO_3D file |
Table 4. ICON output files
| File Name | Format | Description |
|---|---|---|
| INIT_CONC_1 | IOAPI/GRDDED3 | Name and location of the gridded initial conditions data output on the model grid defined by values of VRSN, ICTYPE, APPL, and DATE |
The default location of the ICON output files is the $CMAQ_DATA/icon directory, controlled by the OUTDIR variable in the run script. The default naming convention for all ICON output files uses the APPL and GRID_NAME environment variables in the file name. For initial conditions created from existing CCTM CONC files, the Julian date is also used in the file name through the DATE environment variable. All of the file-naming variables for ICON outputs are set in the run script.
Execute the build script to compile ICON:
cd $CMAQ_HOME/PREP/icon/scripts
./bldit_icon.csh [compiler] [version] |& tee build_icon.log
Set the run script settings according to the execution configuration variables described above. Run ICON to produce initial conditions for the CCTM:
cd $CMAQ_HOME/PREP/icon/scripts
./run_icon.csh |& tee run_icon.log
Check the log file to ensure complete and correct execution without errors.