[Wrf-users] Question regarding determine some parameters in namelist.wps

[Zhixuan Cao]

Thank you Carlos.  Could you check the following statements so that I can confirm that I understand you correctly. 
1) So if giving e_we,  e_sn, dx and dy, the dimension of the computation domain can be determined, right? Choosing of dx and dy is up to me without additional constrain?
2) I should only give dx and dy for the first (coarse) domain, and not necessary to give that for other child domains because they can be inferred from parent_grid_ratio.

I have more other questions (sorry -):
1) How could I know what is the input resolution for each domain? More specifically, if I am using gfs data, I knew from the file name that the resolution can be 0.25 degree, 0.5 degree or 1 degree. What should be the corresponding grog_data_res for this case. 

2) Is there any criteria to determine parent_time_step_ratio?
3) Is there any constrain on determine e_vert? By constrain, I mean, for example, e_we in namelist.input should be consistent with that in namelist.wps.  If not, I can determine e_vert based on desired resolution in vertical direction?
4) How to determine the p_top_requested? 

Thank you again.

Zhixuan Cao

> On Sep 6, 2016, at 1:47 PM, Carlos Ross <cf.ross at gmail.com> wrote:
> 
> Hi Zhixuan,
> You're a bit confused.
> 
> e_we and e_sn are the domain dimensions. in X and Y.
> geog_data_res is the resolution of the input data.
> dx and dy are the resolution of the main domain.
> parent_grid_ratio is the ratio starting from the main domain.
> 
> As example:
> 
>  parent_id         = 1,1,2,
>  parent_grid_ratio = 1,3,3, (resolution of each domain: 27km, 9km, 3km)
>  i_parent_start    = 1,20,15,
>  j_parent_start    = 1,35,15,
>  e_we          = 100,75,60  (domain dimensions: 100x100, 75x75, 60x60 everyone in grid points)
>  e_sn          = 100,75,60
>  geog_data_res = '10m','5m','2m', (input resolution for each domain)
>  dx = 27000, (first domain resolution)
>  dy = 27000,
> 
> 
> 2016-09-03 17:57 GMT-03:00 Zhixuan Cao <hitcaozx at gmail.com <mailto:hitcaozx at gmail.com>>:
> Hi
> I feel confused on the exact meaning of some parameters in namelist.wps, following user manual can not solve my confusion. Could someone give me some advice on this?
> 
> Here do these following parameters work together to determine the resolution of grids for nested domain simulation?
> parent_grid_ratio
> i_parent_start
> j_parent_start
> e_we
> e_sn
> geog_data_res
> 
> 1) If geog_data_res gives resolution of grid, then it seems that I do not need e_we and  e_sn.
> 2) For nested domain simulation, should geog_data_res be consistent with parent_grid_ratio? For example, if parent_grid_ratio = 1, 3 then geog_data_res has to be something like geog_data_res = 9m, 3m.
> 3) In the tutorial, it says that ( e_we = n* parent_grid_ratio +1) and ( e_sn = n* parent_grid_ratio +1).  I guess I can use different n for e_we and  e_sn. Am I right? But is there any constrain on n besides that n has to be a positive integer?
> 
> Thank you very much!
> 
> Zhixuan Cao
> 
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