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How to get the same domain with different resolution


New member

I want to create a 25-km grid covering the same geographical domain as the 50-km. I thought I would be able to obtain that by keeping all parameters in &geogrid (WPS namelist) the same except for e_we and e_sn, which I compute as follows:
e_we [25km] = 2*e_we [50km] - 1
e_sn [25km] = 2*e_sn [50km] - 1
I get similar domains, but not exactly the same. I have tried reducing the number of grid points, but strangely, reducing the number of grid points does not necessarily mean a smaller geographical area covered (i.e., sometimes I get maximum longitudes that are larger than with a smaller number of grid points).

Is there any method/recommendation on how to select e_we and e_sn to obtain a higher resolution grid covering the same domain as a lower resolution grid?

Thanks in advance,

I think what you've described should work -- setting e_we [25km] = 2*e_we [50km] - 1 and e_sn [25km] = 2*e_sn [50km] - 1. I just tested this with an example domain, and the result was as expected.

In the output from the geogrid program, the latitudes and longitudes of the corner points for the domain are provided as the last four entries in the corner_lats and corner_lons global attributes. Could you see whether these match between your 50-km domain and your 25-km domain? For a better description of the corner_lats and corner_lons attributes, you can refer to this section of the User's Guide: The WRF Preprocessing System (WPS) — WRF Users Guide documentation (the table and diagram are at the end of the "Geogrid Output" section, just before the beginning of the "Metgrid Output" section).
Hi Michael,
Thank you very much for the explanation about the corner latitudes and longitudes. I was mainly looking at the mass grid and at the geogrid map with ncl script, so that explains the results I was getting. Looking at the last four entries in the corner_lats and corner_lons global attributes, I see that the corners are the same for both the 50 and 25-km grids.