cycling regional MPAS for purposes of data assimilation

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wrfpup

Member
I would like to run regional MPAS in a cycling mode and be able to assimilate either sounding data or surface data. Currently, I am running a Regional MPAS 12-hour forecast. As such, I generate lateral boundary conditions for each forecast time (every 3 hours) and then the history files. Also, it is outputting one "restart*.nc" file, just for the final forecast hour. I am trying to get the big picture so some very broad questions if I may: 1) what does the restart*.nc file contain? 2) For running MPAS in a 'cycling' mode, I assume I start the forecast cycling back up via the 'restart*.nc' file? 3) and also the matter of updating the LBC's via updated GFS fields...(and eventually assimilating local sounding data/surface data).

I am starting to look at DART for the actual data assimilation portion, but wanted to make sure I can understand how to run Regional MPAS in a cycling mode first.

One note - I saw that some EPA personnel created MPAS add-on code to do data assimilation via obs nudging (2018). This would have been ideal, but this code does not appear to have made it into the current MPAS release. Thus, I was looking toward DART for the data assimilation.

Thanks for any info.
 

wrfpup

Member
I realized I threw in a lot in my queries above. So to simplify things, I will ask this -- How to start an MPAS forecast run via a restart*.nc file? Didn't see a specific example in the user's manual or tutorial about that. Thanks.
 

dashline

Member
hi, I would also like to use MPAS for data assimilation. I would like to ask, what file did you use to run it, restart.xx.nc or history.xx.nc?
 

mgduda

Administrator
Staff member
I'm not particularly qualified to comment on the data assimilation aspect; but, I can offer some answers to the question of how to cycle the model from restart files.

Essentially, the restart files contain the model state that is required to exactly start the model simulation at the point in simulation time when the restart file was written, yielding a simulation that matches bit-for-bit the simulation that would have resulted from running uninterrupted from the initial time. For example, running a continuous, 24-hour integration from 2010-10-23 00 UTC through 2010-10-24 00 UTC should give an identical result to running the model for 12 hours from 2010-10-23 00 UTC through 2010-10-23 12 UTC, writing a restart file, then starting the model up again from that restart file and integrating 12 more hours from 2010-10-23 12 UTC through 2010-10-24 00 UTC.

There are only two namelist options that need to be set in order to restart a simulation from a restart file:
  • set the config_start_time namelist variable to the valid time of a previously written restart file (note that you may have written several restart files periodically until the point where the original model run was stopped); and
  • set the config_do_restart namelist variable to true.

For regional simulations, there's the additional concern of LBCs, and in general, you'll need to ensure that you have valid LBC files through whatever point in time you intend to run the model before stopping (whether the end of a single, one-off simulation, or the end of a cycle). In a cycled DA setup (and assuming 12-hourly cycling for the purposes of discussion), one option may be to re-run the init_atmosphere_model program to produce another set of LBC files valid from the time of the final restart file of the current cycle through the end of the next cycle 12 hours later based on an updated operational forecast from NCEP, ECMWF, etc.

For further explanation of model restarts, you can also refer to:
1) Slides 26 - 28 of the Running MPAS Part 2 tutorial lecture (note, the full set of tutorial slides are linked from the 2021 tutorial agenda).
2) Section 5 of the online tutorial at https://www2.mmm.ucar.edu/projects/mpas/tutorial/Online/ .

I see that we don't actually have a description of the model restart capability in the User's Guide, and this is definitely something that we should remedy!
 
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