Which way is the more computationally efficient for running WRF-Chem with one way nesting: (a) by setting feedback to '0' or (b) using ndown.exe?

[Ankan Sarkar]

Hello everyone,
I want to run wrf.exe (WRF-Chem) with one-way nesting because of the limitations of my system (a linux server with 378 GB of RAM and 32 processors). I have gone through the WRF user guide, which explained how to do one-way nesting using 'ndown.exe'. Also, I found the following lines on the webpage (WRF Namelist.input Best Prac):
"When feedback is off , it is equivalent to a one-way nested run, since nest results are not reflected in the parent domain."
So, my question is: Are both processes equally efficient as far as computational cost is concerned? Or is using 'ndown.exe' faster than setting 'feedback' to '0'?
Can anyone please guide me in this regard? That will be greatly appreciated.
Thanking you.
With regards,
Ankan

[Rajesh Kumar]

Hi Ankan,

If you have limited resources, I recommend one-way nesting because if you use two-way nesting, you need memory to hold the variables for both the domains at the same time which may be an issue with limited computing power and can cause segmentation fault. 

Rajesh

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Rajesh Kumar, Project Scientist III

Research Applications Laboratory 

National Center for Atmospheric Research 

E-mail: rku...@ucar.edu

Phone: +1-303-497-1413

Web: https://staff.ucar.edu/users/rkumar

[Ankan Sarkar]

Dear Sir,

Thank you for your reply. I want to use one-way nesting because of this reason you mentioned. But, my question is:  Are both processes (i.e., (a) by setting feedback to '0' in the namelist.input or (b) using ndown.exe for providing the boundary conditions to the nested domain) equally efficient as far as computational cost is concerned? Or is using 'ndown.exe' faster than setting 'feedback' to '0'?

Thank you for your time and consideration.

With best regards,

Ankan

[Mary Barth]

Ankar,

I don't know as I use only the ndown.exe method. You may want to ask on the WRF forum page.

- Mary

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[Ankan Sarkar]

Okay, Mam. Thank you for your response.

With regards,

Ankan