…or, how to change your history interval mid-run for WRF.
Here is a funny problem: I’m running a rather long WRF (or WRF-GC) case where I have to spin-up chemistry for about a month before I run the remaining time in the simulation.
The spin-up period history output is no use to me, but as a sanity check I want to output every 12 hours to see if things are going OK. Then for the main simulation period I want hourly output.
The reason I do this is because (1) storage is constrained and I don’t want to hog the server with useless output (and wake up in the middle of the night to delete useless data) and (2) core hours are constrained and I might get kicked out of the queue, so it’s better to do this in a few restart runs in WRF.
How can I do this? The logical thinking is to run the spin-up first with
&time_control ... history_interval = 720, 720, 720, frames_per_outfile = 1, 1, 1, restart = .false., restart_interval = 10080,
10080 is number of minutes between restart files being written (24 x 7 x 60 = 10,080). Then once I am done with the spin-up, I can simply restart by killing the job, and modifying the namelist like so:
&time_control ... history_interval = 60, 60, 60, frames_per_outfile = 1, 1, 1, restart = .true., restart_interval = 10080,
Nope! This won’t work. Apparently, WRF stores the history alarm (WRF jargon for “when is history going to be written next?") inside the
wrfrst restart files generated. How do I know this?
Because I ran about a week into my simulation and realized I had no hourly output.
Oops! Let’s poke into
wrfrst and see what we can find:
$ ncdump -h wrfrst_d01 > reset.txt ... // global attributes: :TITLE = " OUTPUT FROM WRF V126.96.36.199 MODEL" ; :START_DATE = "2019-04-02_00:00:00" ; :SIMULATION_START_DATE = "2019-04-02_00:00:00" ; :MAX_WRF_ALARMS = 55 ; :WRF_ALARM_ISRINGING_01 = 0 ; :WRF_ALARM_SECS_TIL_NEXT_RING_01 = 43200 ;
43200 just so happens to be 720 minutes (720 x 60 = 43,200 seconds) and checking the WRF source confirms this somewhat:
01 is the history alarm.
Can I do something sneaky and change
history_interval in the restart file? Luckily, yes - it would be kind of stupid to re-run the whole spin-up because of a namelist issue. NCO to the rescue. Copy your restart files, prefix them with
old_ for backup and do this for each domain:
ncatted -O -h -a WRF_ALARM_SECS_TIL_NEXT_RING_01,global,m,i,3600 old_wrfrst_d01_2019-04-30_00\:00\:00 wrfrst_d01_2019-04-30_00\:00\:00
m means modify the global attribute,
i is integer, and
3600 is the desired
history_interval in minutes.
All done! Core hours and storage are both saved by this little trick.