[Wrf-users] Different results with different processor count with WRF

[HONG]

All,

I believe that the native output should be the bitwise exact irrespective of the number of CPUs in parallel computers.
It is hard to define the tolerance in differences due to software systems in regional models, but the above is the 
pre-requiste. 

Please find the attached for your reference.

songyou hong




SONG-YOU HONG, Director
Korea Institute of Atmospheric Prediction Systems (KIAPS)
4F, 35 Boramae-ro-gil, Dongjak-gu
Seoul 156-849, Korea
Web : http://www.kiaps.org
E-mail: songyou.hong at kiaps.org, songyouhong at gmail.com
Phone :82-2-6959-1601,  82-10-2025-2679 





2014. 4. 25., 오후 7:46, Vaibhav Saxena <saxena.vaibhav at gmail.com> 작성:

> Hi All, 
> 
> I am seeing a large difference in results when running WRF on different processor counts. I am running WRF 3.5.1 in (dm+sm) mode with 3 nested domains on Blue Gene/P. WRF is run in SMP mode on BG/P with 4 threads per MPI process and 1 MPI process per node. The model is run to produce a 48-hour forecast. Using the innermost nest forecast files (wrfout), I am comparing the accumulated precipitation forecast for a particular lat/long at the end of simulation (48 hours) when using 512, 256 and 128 BGP nodes.  
> 
> Forecasted values for precip look like this:
> 512 nodes - 54 mm
> 256 nodes - 16 mm
> 128 nodes - 7 mm
>  
> I have following Qs:
> 1. Is it true that WRF may produce incorrect results when the number of grid points per patch (assigned to an MPI process) or per tile (assigned to a thread) is less than 10x10 ? If this is correct, is it per patch or per tile ? The question arises because for 512 nodes, for our domain size, each patch has 8x17 grid points but for 256 and 128 nodes, there are more than 10x10 points per patch. 
> 
> 2. Are issues mentioned in http://mailman.ucar.edu/pipermail/wrf-users/2012/002944.html still valid in WRF 3.5.1 ? Can these issues produce such a large difference ? 
> 
> Thanks in advance. 
> - Vaibhav
> 
> 
> -- 
> email: saxena.vaibhav at gmail.com
> _______________________________________________
> Wrf-users mailing list
> Wrf-users at ucar.edu
> http://mailman.ucar.edu/mailman/listinfo/wrf-users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ucar.edu/pipermail/wrf-users/attachments/20140428/c5bcbddc/attachment-0002.html 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: software-hongetal-2013.pdf
Type: application/pdf
Size: 1527476 bytes
Desc: not available
Url : http://mailman.ucar.edu/pipermail/wrf-users/attachments/20140428/c5bcbddc/attachment-0001.pdf 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ucar.edu/pipermail/wrf-users/attachments/20140428/c5bcbddc/attachment-0003.html