[RegCNET] Nan error during model run

[Sara Rauscher]

Dear Dwijenra,

This is the most common question on the list (in fact, it was answered 
the other day). Everyone, please read the user's guide! It contains 
valuable information that will help you run your simulations.
http://users.ictp.it/RegCNET/regcm.pdf

The model is sensitive to the time step used. The first rule of thumb is 
to use 3 times the horizontal grid spacing. In your case, 60 km, so 180 
is the best to start with. However, in cases of steep topography you may 
need to decrease this time step. You might want to try 150, for example.

If you are doing a long simulation, and this just happens once or twice, 
you can work around this. Set the time step to a lower value, restart 
the model to a point before where it blew up, and then after this point, 
stop the model, put the time step back to its original value, and 
restart the model. So for example, if my model had died on January 5th, 
I would probably restart at the beginning of January, do that month at a 
lower time step, and then continue the simulation in February at the 
original time step if that's been working. Note that this is acceptable 
to do once or twice in a long simulation (like > 5 years), but if it 
happens more often, you should restart the simulation from the beginning 
at a shorter time step.

In the regcm user guide, there is a table that gives suggestions (these 
are just suggestions) for time steps for different grid spacing (Table 
12, page 40):
Table 12: Time steps with different resolutions:

dx(km) dt(sec) abatm(sec) abemh(hr) radfrq(min)
10 30 90 18 30
20 60 120 18 30
30 100 300 18 30
45 150 300 18 30
50 150 450 18 30
60 200 600 18 30
90 225 900 18 30

There is discussion of how to set the time step on page 35 in the user's 
guide.
cheers
sara


d d wrote:
> Dear RegCNET Users,
>
> I am having similar problem as Dr. Satyaban  getting the NaN error  
> while running RegCM for 6 months simulation. The ICBC files are OK 
> when i checked them on grads. The Model can run successfully upto 4 
> months and after that it encounters NaN error for last two months.
> I had tried to restart the simulation but still the same
> domain.param configuration
> Idate1=1997010100 start day of simulation
> Idate2=1997063000 End day of simulation
> ds = 60km
>
> regcm.in <http://regcm.in> configuration
> Idate0=1997010100
> Idate1=1997010100
> Idate2=1997063000
> dt=180
> radfrq=30
> abemh=18
> abatm=540
>
> please kindly suggests whar might be the problem
>
> Best regards
> Dwijendra
>
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-- 
Sara A. Rauscher
T-3 Fluid Dynamics
MS B216
Los Alamos National Lab
Los Alamos, NM 87545 USA
(505) 606-0512