[FEATURE REQUEST] Turn off writing initial checkpoint file

[lizziel]

Default values in GCHPctm 13.0.0-alpha.2 (and all previous GCHP versions) write a MAPL internal state checkpoint file during the first timestep. At high resolutions this adds significantly to the run-time. We should have the ability to turn off writing this first checkpoint file. It shouldn't be needed since we already have a restart file and the output checkpoint file is written separately at the end of the run.

[lizziel]

In GCHP 13.0.0 the default of writing periodic checkpoints is turned off. This avoids writing a restart file at simulation start.

Configuring periodic checkpoint writes, either at regular or irregular intervals, is now an option from runConfig.sh. It is always off by default for all newly generated run directories. If periodic checkpoint write is turned on with regular frequency, then a restart will still be written at run-time start. As was the case before this update, it will be filled with zeros. This is due to the location of file write relative to population of internal state in the execution sequence.

Completely avoiding writing a restart filled with zero at run-time start while also have regularly scheduled checkpoint writes is doable. However, it requires setting the checkpoint ref date and time to be just prior to simulation start time, thereby making the interval between start and first checkpoint file shorter than the interval between subsequent checkpoint files. Doing this will require some custom adaptation of runConfig.sh. If you interested in this I encourage you to try it!