[Wrf-users] Tests with adaptive time step in WRF-ARW (v3)

[Hutchinson, Todd]

Eduardo,
 
Glad to see that you are working with the adaptive time-step.  As I'm
sure you know, it is new in WRF3.0.  We developed and have been using
the adaptive time-step in operational forecasts with a modified version
of WRF2.2 for quite some time.  Our operational simulations consist of
an outer 12km nest and an inner 4km nest.   This configuration has been
very stable for us.  However, we have only done limited testing with
three levels of nesting.
 
I'm interested to see the length of the time-steps just before the model
crash.  Could you post the last hundred or so "Timing for main" lines
from the rsl.out.0000 file?
 
Have you set any parameters in the namelist file other than the
use_adaptive_time_step setting?
 
I'd suggest that you add the following to your namelist file:
max_step_increase_pct = 5, 51, 51   (the default is 5,5,5)
 
This will limit the time-step of the outer nest from changing by more
than 5%, but allow the time-step on the inner two nests to change by up
to 51%.  Since the inner nest(s) time steps must be evenly divisible
into the outer nest time-step, with the default of 5,5,5, the time step
on the inner nests will not increase unless the time-step on the outer
nest changes.  
 
Just FYI:
I believe the 'WOULD GO OFF TOP" lines that you see are a symptom of the
model being unstable.  I've seen these types of errors in several
situations:
1) a couple of minutes into a simulation -- often this is caused by bad
input data
2) later on during a simulation -- this is most often caused by a
time-step problem, or bad boundary data.

________________________________

From: wrf-users-bounces at ucar.edu [mailto:wrf-users-bounces at ucar.edu] On
Behalf Of Eduardo Penabad Ramos
Sent: Tuesday, June 17, 2008 11:37 AM
To: wrf-users at ucar.edu
Cc: 'wrfhelp'
Subject: [Wrf-users] Tests with adaptive time step in WRF-ARW (v3)


Hello!
 
we are running a setup of 3 nested grids with WRF-ARW (v3) over Galicia
(NW Iberian Peninsula), with dx=36,12 and 4 km.
 
We are testing the adaptive time step with this grid configuration, and
with the following set of physics:
 
Radiation: Longwave RRTM, Shortwave MM5-Dudhia
PBL: YSU (with sfclay: Monin-Obukhov from MM5 MRF)
Surface: 5 layer MM5 LSM
Cumulus: Kain-Fritsch
Microphysics: WSM6
 
With this setup we have experienced some problems related with
Kain-Fritsch (we guess). After about 40-50 hours of simulation, error
messages appear in the WRF output textfiles:
WOULD GO OFF TOP: KF_ETA_PARA I,J,DPTHMX,DPMIN
where NaNs appeared for DPTHMAX
We have tested with Betts-Miller-Janjic cumulus parameterization, and
although no error messages appeared, wrfout files also have some NaNs
inside.
 
Do you have any suggestions? Thanks in advance!
 
Eduardo Penabad
MeteoGalicia
 
 
 
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