## Equation for calculating e_we, e_sn, i_parent_start, j_paren

All things relating to the WRF Domain Wizard tool

### Equation for calculating e_we, e_sn, i_parent_start, j_paren

Hi,

Is there any equation for calculating e_we, e_sn, i_parent_start, j_parent_start to write a automatic program by using resolution, corner boundary values and central latitude and longitude for parent and nests for any projection for any location in the globe for WRF_ARW.

I tried to understand the WPS code, but i unable to get the clear picture.

Please share your views.

Thanks & Regards,
mallesh4science

Posts: 11
Joined: Wed May 22, 2013 4:49 am

### Re: Equation for calculating e_we, e_sn, i_parent_start, j_p

Hi,

Just in case some sees this post. i_parent_start and j_parent_start are the number of cells counted horizontally to the right and vertically up, respectively, from the lower left corner of the parent domain to the point where the nested domain starts. e_we and e_sn are the ending points of the grids, that is to say, the NUMBER OF CELLS (horizontally and vertically) THAT EACH GRID HAS.

Take a look at the figure in section "Creating Nested Domains with the WPS" from http://www2.mmm.ucar.edu/wrf/users/docs ... chap3.html

Also, you can't just assign a random number of cells to a nested domain, you have to make sure that it fits into its parent. The criterion to follow is that e_we and e_sw must be one greater than an integer multiple of the parent_grid_ratio (check section "How to add a new WRF geographical domain" from https://meteo.unican.es/trac/wiki/WRF4GTutorial2 ).

Let me explain myself:

In your namelist.wps you have

&geogrid
parent_grid_ratio = 1, 3,
i_parent_start = 1, 36,
j_parent_start = 1, 14,
e_we = 100, 142,
e_sn = 67, 85,

This means that your nested domain starts at the 36th cell to the right and at the 14th cell to the top, starting from the lower left corner of the parent domain.

For the first (or parent) domain, e_we and e_sn have no restriction. For the second domain, parent_grid_ratio = 3, so e_we and e_sn must be one greater than a multiple of 3. And there you have 142-1=141 which is divisible by 3, and 85-1=84 which is also divisible by 3.

And Bob's your uncle!
Hydrology Researcher, University of Bristol
alainaketh

Posts: 36
Joined: Fri Jun 26, 2015 12:30 pm

### Re: Equation for calculating e_we, e_sn, i_parent_start, j_p

13.46N,79.2E this is my latitude and longitude. Please try to help me to find out the following
&geogrid
parent_id = 1, 1, 2,
parent_grid_ratio = 1, 3, 3,
i_parent_start =
j_parent_start =
e_we =
e_sn =
geog_data_res =
dx =
dy =
map_proj = 'mercator',
ref_lat =
ref_lon =
truelat1 =
truelat2 =
stand_lon =
Jipson Johnson

Posts: 24
Joined: Thu Jan 08, 2015 2:15 pm

### Re: Equation for calculating e_we, e_sn, i_parent_start, j_p

There is a useful tool in ncl to get ij from any lon lat: wrf_user_ll_to_ij
https://www.ncl.ucar.edu/Document/Funct ... o_ij.shtml

See especially example 1 and use loc = loc-1
jgc

Posts: 3
Joined: Mon May 18, 2009 7:40 am

Return to WRF Domain Wizard

### Who is online

Users browsing this forum: No registered users and 1 guest