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Use ndown at times other than 00/06/12/18 UTC

J

JiaWang

New member
I want to use ndown to generate initial and boundary conditions for D02 at time other than 00/06/12/18 UTC. Say I want to use ndown to generate the IC and BC for D02 at 02 UTC.

In order to use the ndown, I need wrfout_d01_xxx and wrfndi_d02 (at 02 UTC), and wrfndi_d02 is actually wrfinput_d02.

But since my target time is 02 UTC, how could I generate wrfinput_d02 at 02 UTC?
 
Hi,
Do you mean that you want to run the initial wrf simulation, starting at d02, as well, or is that run starting at a different time (i.e.. at one of the boundary times - assuming your boundary conditions are every 6 hours)? If you want to start them at different times, I don't believe the ndown program will allow that. It is very finicky and requires the times to match exactly.

If you want both domains to start at time 02, you can try to output met_em* files every hour, so that you'll have the files available at the 02 hour and you can start the simulation from there.
 
If you change the variable "interval_seconds" in namelist.wps to 3600, the metgrid program will create hourly input, just interpolating the 3-hourly data to the hourly data files.
 
Ungrib won't interpolate the data - it will simply process the files you have, but metgrid will interpolate them, so that you will then have a met_em* file available each hour. Give it a try and see!
 
I have tried, with GFS 3-hourly dataset.
(1) When I used "interval_seconds=10800" for geogrid and ungrib, then used "interval_seconds=3600" for metgrid, it failed.
(2) When I used "interval_seconds=10800" for geogrid, then used "interval_seconds=3600" for ungrib and metgrid, it worked.
In the ungrib step, since GFS only available at 3-hourly interval, the ungrib will look for two adjacent time steps, then do the interpolation.
 
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