CCTM run at less than 1 hour timestep

CMAQ
1

Hi,
Is it possible to run CCTM by making use of WRF meteorology data output at 15 min (<1 hr) intervals? If so, how? This is really important as in 1 hour many things can happen - especially for highresolution models.

Thanks.

2

I think it should be possible – the I/O API INTERP3() function that it uses was designed to handle the business of time steps without the modeler having to worry about it.

The original version of the model was quite happy with almost anything that makes sense – even such things as mixing up time steps for the various input files, even correctly handling silly things like:

  • METCRO2 25 minutes
  • METCRO3 17 minutes
  • METDOT3 23 minutes
  • EMIS3D 39 minutes

Be aware, however, that there has been a lot of unnecessary hard-coded one-hour/one-day programming since then ;-(

And watch out for the scripts, too!

3

Thank you, for the reply. But I am not sure about how would I tell the model to take in my meteorology data ever 15 minutes, in the CCTM run script? Ideally I would like to have model simulation that would take in meterology data at 15 minutes interval but other emission data at 1 hour.

I mean in the CCTM run script

#> Set Timestepping Parameters
set STTIME = 000000 #> beginning GMT time (HHMMSS) <<<<----------------
set NSTEPS = 240000 #> time duration (HHMMSS) for this run <<<<----------------
set TSTEP = 010000 #> output time step interval (HHMMSS) <<<<----------------

How would I set up the NSTEPS? Doing 15*24 may not make sense because still the length of the run for 1 day is just 24 hours?
Thank you.

4

That’s the point of INTERP3 – you shouldn’t need to tell the model what the file’s time steps are.

You had better checkthe model-code on how it does precipitation-rates, though; I think that may be hard-coded at one hour and will need fixing.

– Carlie

5

Okay, thank you for the clarification. I will just keep at 1 hour for now! I wish < 1hr capability be implemented in the model (that could be more relevant for short lived phenomena like dust storms).

6

Hi,
Have you tried setting INTVL to 15 minutes in the run_mcip script? I believe it defaults to 60 but there’s no constraint that it has to be hourly. As @cjcoats said, there may be some other hard-wired code to worry about, but it’s worth a try.
Megan

7

Yes, mcip has no problem in outputing at 15 minutes!

1 Like
8

To run CCTM with finer scale meteorology inputs, you have two options:

  1. Run the model by providing the model temporally fine MCIP generated meteorology, that is at a temporal resolution that is greater than the sync step of the model (i.e. >5 mins, depending on your domain). To do this you must also set the TSTEP, a runtime environmental variable controlling the output time step interval, to be equivalent to the temporal resolution of your MCIP output. Note that this approach will increase the disk I/O needed to run the simulation as the temporal resolution of your output data will be the same as your meteorology data. Our developers are currently working on an implementation that will allow users to run with temporally finer scale meteorology, while independently specifying an output step that is a multiple of the sync step.

  2. Run the Two way coupled model (WRF-CMAQ), as it was designed to allow for frequent data exchange between the meteorology and atmospheric chemistry components of the model system without increasing the level of disk I/O need to run fine scale simulations. Instructions to run the two-model can be found here: https://github.com/USEPA/CMAQ/blob/master/DOCS/Users_Guide/CMAQ_UG_ch13_WRF-CMAQ.md, if you decide to pursue this option.

9

Thank you for the reply. Just a quick follow up: suppose the meteorology is hourly data but the emission dataset is sub-hourly (say, every 15 minutes); will the model be reading emission data every 15 minutes from the file, while reading meteorology every hour? (TSTEP is set at 15 minutes). The question is: ‘is it mandatory to have the same time steps in any kind of inputs, or it can be different?’ The model seems running with hourly meteorology and 15 minutes emission files but I am not sure if it is reading from the emission file every 15 minutes rather than interpolating.

Thank you.