[RegCNET] Re: Sigma Levels

Neil Davis nndavis at unity.ncsu.edu
Fri Oct 28 14:40:09 CEST 2005


I tried this suggestion by changing the timesteps to those listed in the 
manual as being good for a dx of 50 km,  So I changed dt from 200 to 150 
and abatm from 600 to 450 and now the job is running on the larger 
domain.  Thanks everyone for the suggestions and help.  I am wondering 
if there is an intermediate change that I could attempt however just to 
save some computational time.  I wasn't sure if the timestep values had 
to be set to certain values or if I could change them some as long as 
abatm is 3 tims as large as dt. 

Neil Davis

Solmon Fabien wrote:
>
> Hi Moet !
>
> Did you try to play also with the time step on the big domain ?  the 
> vertical advection is sensitive to sigma level change, I would guess 
> that if you have a high vertical velocity in a part of the domain  you 
> need a smaller time step if you reduce the grid step ....    cheers
>
> fabien
> moetasim wrote:
>
>> Hi Jeremy , Bi n All,
>>
>> Neil and I are trying to figure out the reason why he has floating 
>> point exception (FPE) while running RegCM with his modified sigma 
>> levels. What we got finally is that regcm works fine with his 
>> modified levels at a relatively smaller domain than the one which 
>> ends up with FPE. I had actually tried to run regcm with his modified 
>> levels at a smaller domain and found that it works fine. Same kind of 
>> result he got when he ran the model with his modified levels but, 
>> smaller domain. I can't really say anything with confidence that why 
>> is it happening? He has domain size = 74 x 136 x 23 for the 
>> simulation which ends up with FPE. The same domain works fine if he 
>> runs the model without modifying sigma levels.
>> Is it happening because his modified levels are more concentrated in 
>> low level (say in PBL) which is making it more computationally tough 
>> for PBL model or what else? There is no reason other than 
>> computationally incompatibility to end up with a FPE for larger 
>> domain + modified sigma levels, if model works fine for both small 
>> domain + modified sigma levels, and larger domain + default sigma 
>> levels (its my point of view).
>>
>> (I have attached the gradual progress to this conclusion here under)
>> MOet
>>
>>
>> Quoting Neil Davis <nndavis at unity.ncsu.edu>:
>>
>>  
>>
>>> I tried running the 50 X50X23 and that seems to be working, it has 
>>> run through the first month already so I am assuming that that 
>>> works.  I am just wondering why the default 23 sigma levels would 
>>> run on my large domain, when the proposed ones do not.  Is there 
>>> something with the stacking in the lower levels that adds computer 
>>> memory or something that I am missing.
>>> Thank you again for all your help on this problem,
>>> Neil Davis
>>>   
>>
>> Quoting moetasim <mashfaq at purdue.edu>:
>>
>>  
>>
>>> To be on safe side just make a check with small domain like 50 x 50 
>>> x 23!
>>>
>>>
>>>
>>>
>>>
>>>
>>> Quoting Neil Davis <nndavis at unity.ncsu.edu>:
>>>
>>>   
>>>> How much of a decrease would you suggest?  I did run the identical 
>>>> domain with the default 23 vertical levels.  I am running the model 
>>>> on an IBM blade cluster running redhat linux.  Glad to hear that 
>>>> the model is running somewhere with my proposed sigma levels.  I 
>>>> will try your suggestion of a smaller domain and see if that fixes 
>>>> it. Neil
>>>>     
>>
>> Quoting moetasim <mashfaq at purdue.edu>:
>>
>>  
>>
>>> Hi,
>>> I have an early conclusion for your problem, now. It seems that 
>>> increase   
>> in  
>>
>>> vertical resolution and considerably large domain (that you have for 
>>> your experiment) is creating the crash. You may prove me right/wrong 
>>> by just decreasing your domain size and running the model. I had 
>>> read previously   
>> that
>>  
>>
>>> you mentioned RegCM working fine with its default defined 23 sigma 
>>> levels.
>>> Did you run that experiment with same domain size as its in this 
>>> case of your modified sigma levels experiment.
>>>
>>> Once you are done with with your problem, I will post the final 
>>> answer at RegCNET. By the way, model is running without any problem 
>>> at my end with   
>> your
>>  
>>
>>> proposed sigma levels. Which machine do you have for running RegCM?
>>>
>>> MOet
>>>
>>>
>>>
>>> Quoting Neil Davis <nndavis at unity.ncsu.edu>:
>>>
>>>   
>> Quoting moetasim <mashfaq at purdue.edu>:
>>
>>  
>>
>>> I have started running RegcM with your defined 23 sigma levels..At 
>>> the   
>> moment
>>  
>>
>>> it running..lets see hw it goes..
>>>
>>>   
>> Quoting moetasim <mashfaq at purdue.edu>:
>>
>>  
>>
>>> Yeah just make sure that every thing is fine for 3D variables 
>>> written in   
>> ICBC
>>  
>>
>>> files.
>>>
>>>   
>> Quoting Neil Davis <nndavis at unity.ncsu.edu>:
>>
>>  
>>
>>> I have attached the output and the error log of the model run.  This 
>>> time it didn't seem to even start a few days.  I will try your other 
>>> suggestions now, although what did you mean by check icbc at 
>>> different sigma levels, just look at the ICBC files and see if the 
>>> values look reasonable?
>>> Thanks again for your help
>>> Neil
>>>
>>>
>>>
>>>   
>>
>> Quoting moetasim <mashfaq at purdue.edu>:
>>
>>  
>>
>>> Ok, can you send me the output that you get after running regcm.x 
>>> (start   
>> to  
>>
>>> the point where FPE occurs).
>>>
>>> and for the time being:
>>>
>>> 1) check icbc at differnt sigma levels. If everything is fine there 
>>> and   
>> tell
>>  
>>
>>> me.
>>>
>>> 2)Also, try to run the model with reduced time step and let me know 
>>> what happens.
>>> But before this send the ./regcm.x output.
>>>
>>> MOet 
>>>
>>> Quoting Neil Davis <nndavis at unity.ncsu.edu>:
>>>
>>>   
>>>> Sorry, the exception takes place when running the model.  It goes a 
>>>> few time steps then the error occurs.  ICBC and Terrain seem to 
>>>> have no errors when I run them.
>>>>
>>>>
>>>>     
>>> -- 
>>>
>>>   
>>
>> Quoting moetasim <mashfaq at purdue.edu>:
>>
>>  
>>
>>> But you didnt tell me at what step yuo have floating point exception?
>>> Terrain, ICBC or while executing model?
>>>   
>>
>>
>> Quoting Neil Davis <nndavis at unity.ncsu.edu>:
>>
>>  
>>
>>> I just changed in terrain.f the lines 1423 to 1448 to this
>>> else if(kz.eq.23) then                  ! MM5V3
>>>         sigma(1) = 0.0
>>>         sigma(2) = 0.05
>>>         sigma(3) = 0.1
>>>         sigma(4) = 0.16
>>>         sigma(5) = 0.23
>>>         sigma(6) = 0.31
>>>         sigma(7) = 0.39
>>>         sigma(8) = 0.47
>>>         sigma(9) = 0.55
>>>         sigma(10)= 0.61
>>>         sigma(11)= 0.66
>>>         sigma(12)= 0.69
>>>         sigma(13)= 0.72
>>>         sigma(14)= 0.75
>>>         sigma(15)= 0.78
>>>         sigma(16)= 0.81
>>>         sigma(17)= 0.84
>>>         sigma(18)= 0.87
>>>         sigma(19)= 0.9
>>>         sigma(20)= 0.93
>>>         sigma(21)= 0.96
>>>         sigma(22)= 0.98
>>>         sigma(23)= 0.99
>>>         sigma(24)= 1.0
>>>      else
>>>
>>> moetasim wrote:
>>>   
>>>> let me have a look at your changes.
>>>>
>>>> MOet
>>>>
>>>> On Tue, 25 Oct 2005 09:36:08 -0400, Neil Davis wrote
>>>>  
>>>>     
>>>>> I am working with RegCM over tropical Africa and want to adjust 
>>>>> the sigma levels in the 23 level setting so that there are more 
>>>>> levels below 3000 m than in its current set up.  I have been able 
>>>>> to run the model with the default 23 sigma levels but when I try 
>>>>> to change it to increased levels in the lower atmosphere I get a 
>>>>> floating point exception.  I was wondering if it is at all 
>>>>> possible to change the sigma levels from the default, and if it is 
>>>>> possible what could be causing the floating point exception.  I 
>>>>> can post my adjusted sigma levels if that will help.
>>>>>
>>>>> Neil Davis
>>>>> NCSU climate modeling lab
>>>>>
>>>>>       
>>
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