[RegCNET] Re: Sigma Levels

Solmon Fabien solmon at ictp.trieste.it
Thu Oct 27 10:08:20 CEST 2005


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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>  
>


-- 
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FABIEN SOLMON
Physics of Weather and Climate Section
The Abdus Salam International Centre for Theoretical Physics
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