Possible to output history for only specific months?

[khartig]

I am planning to do some F-compset runs of CESM2 at fixed CO2 that cover multiple decades and need history output for multiple large variables like temperature and winds at high time resolution (every hour). The history files take up a lot of space, and writing the files seems to slow down the run by a factor of about 2. However, I only really need history files for the winter months, so I would rather the model didn't write any history at all in other seasons. Is there a way to output history files for only specific months from CAM?

When I did a similar run with CESM1-CAM5, I ended up just deleting the history files for all the other months in between resubmits, but the model was still slowed by having to write those files in the first place. I ran the first 4 model years with no user-specific history outputs and it completed in 10 hours on 288 cores, but when I made a branch run and included history files in user_nl_cam I could only run 2 model years in each 12-hour submission on the same number of cores. Any help to let me speed up my runs or use less storage space would be greatly appreciated!

 

[sacks]

I don't think there is a way to only produce high-frequency output for parts of the run. (I could imagine doing this via a workflow that creates separate branch cases for each winter vs. the rest of the year – so you'd have two cases for each year. But this might be messy to set up and even messier to combine things together for the final output, so I'm not sure if it's worth pursuing that approach.)

I'm going to move this to the CAM forums in case anyone there has more insight.

 

[khartig]

Thanks for the quick reply! I had a similar thought, but also concluded it would get too messy to have new branch runs every year. And from what I understand, user_nl_cam can't be changed mid-run, so I also can't just switch out the requested variables every few months.

 

[sacks]

And from what I understand, user_nl_cam can't be changed mid-run, so I also can't just switch out the requested variables every few months.

Right, at least for history variables like this (unless there are new capabilities that I am unaware of).

 

[cacraig]

I agree with Bill's assessment that aside from starting/stopping the model each time you want to change the user_nl_cam, there is not a solution to this.

One other thing to consider, is removing unnecessary output fields from your history files. There are several namelist settings which can help you in this regard. You can either do a fexcl of the fields you don't want, or set empty_htapes to true and then add back in the fields you want to output via fincl.

You probably know where the documentation for the namelist variables is located, but just in case you do not, it is at: CESM2 CAM6.3 Namelist Definitions