[Wrf-users] query on nesting

[Jyothi N]

Hi everyone

I am using WRF-ARW with multiple nesting. For a set of experiments, I have multiple nests at relatively coarse resolutions moving from the inner to the outermost, and a minute innermost nest, which resolution I wish to vary from finest to coarse, and study its sensitivity. In all the experiments, the physical locations of all the nests are unchanged. I am only interested in varying the resolution of the innermost nest.

In this situation, is it alright if 

(i) I keep the resolution and number of grid points of all the outer nests unchanged and only vary the parent-grid ratio of the innermost domain, wrt its immediate parent domain, for studying its sensitivity,  i.e., in this situation, I would have parent-grid ratios as:
1, 3, 3, 5, 3
1, 3, 3, 5, 5
1, 3, 3, 5, 7  and so on, 1, 3, 3, 5, 17, etc, going to finer and finer resolution of the innermost nest.

or 

(ii) is it physically more appropriate to maintain the parent-to-child grid ratio constant for all the nests and vary the number of grid points accordingly instead, to maintain the same physical area, and thereby study the sensitivity of the innermost nest (which is my main concern)? In this situation, I would have parent-grid ratios constant, as: 1, 3, 3, 5, 3, all along, but will have to change the number of grid points on all the nests accordingly instead, to change the resolution of the innermost one from finer to coarser.

If I go by the former case, will I be messing up the feedback between the parent and nest, by changing the parent-grid ratio of the innermost nest alone, leaving all the other nests unchanged? For instance: if i chose a parent-grid ratio of 17 for the innermost one, and leave the outer nests unchanged, I would have a situation  like, a 2 km inner nest feeding back onto something like a 40 km immediate outer nest! In which case, is the latter one a better alternative then?

I will be grateful for any suggestions on this.

Jyothi
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