How are IC specified for Free Forecast Jobs - TerrenceMcGuinness-NOAA/global-workflow GitHub Wiki

The initial conditions for a forecast in your workflow are determined by both the initial date (idate) and the configuration settings in your YAML file and environment variables. Here's how it works:

The initial conditions for a given forecast are specified in the configuration files and environment variables.

In C48_ATM.YAML, the initial date idate is set:

idate: 2021032312

The script stage_ic.sh sets up the initial conditions by executing JGLOBAL_STAGE_IC. This script uses environment variables like COMINgfs defined in

JGFS_ATMOS_WAFS_GCIP

export COMINgfs=${COMINgfs:-$(compath.py ${envir}/${NET}/${gfs_ver})/${RUN}.${PDY}/${cyc}/$COMPONENT}

Additionally, in config.base, the initial date SDATE is set:

export SDATE=@SDATE@

So is that it, how do I know what all the specific files are?

The paths to the initial condition files are specified through these environment variables, which are configured based on the specific machine and runtime settings.

Initial Date (idate):
- In C48_ATM.yaml, you have specified:
```
idate: 2021032312
```
  This sets the initial date and time for the forecast (March 23, 2021, at 12 UTC).
Resolution and Model Configuration:
- The resdetatmos parameter sets the atmospheric resolution:
```
resdetatmos: 48
```
  This means you're running a C48 resolution model.
Workflow Scripts and Environment Variables:
- The script stage_ic.sh

executes JGLOBAL_STAGE_IC: bash "${HOMEgfs}/jobs/JGLOBAL_STAGE_IC"

Inside JGLOBAL_STAGE_IC, environment variables like COMINgfs are used to construct paths to the initial condition files:
```
export COMINgfs=${COMINgfs:-/path/to/input/data/gfs.${PDY}/${cyc}/atmos}
```
- PDY is the date in YYYYMMDD format extracted from idate.
- cyc is the cycle hour (HH from idate).

Determining Specific Files:
- The workflow expects the initial condition files to be in a specific directory structure based on idate and resdetatmos.
- For a C48 forecast starting at 2021032312, the path might be:
```
/path/to/input/data/gfs.20210323/12/atmos
```
- Required files could include atmospheric variables, surface fields, etc.
Machine-Specific Paths:
- Machine-specific configurations can be set in environment modules or configuration files.
- Variables like HOMEgfs, COMROOT, and EXPDIR define paths relevant to your machine.

Summary:

The idate provides the forecast start time.
The resolution (resdetatmos) and other settings define which initial condition files are needed.
The workflow scripts use these parameters to construct the paths to the required files.
Additional environment variables and configuration files specify machine-specific paths and settings.

If you need to customize which initial condition files are used or their locations, you'll need to adjust the relevant environment variables or update the workflow scripts accordingly.