## Activity 2: Designing Nested Domains

In this Activity, we will learn how to design nested domains. You should attempt the activity only after you have read and studied this week's Tutorial. There, you will learn the skills needed for you to complete this task.

Working with nests in WPS is not complicated. You need to be aware of a few things, such as:

• The more nests you add, the slower your experiment will get
• Always remember to use a ratio for the nest, such as the 3:1 ratio we have studied
• You will need to tell namelist.wps the number of domains you will be working with. So, for example, if you have an experiment with 30 km (parent domain), 10 km (first nest) and 3.3 km (second nest), then you have a total of 3 domains. This needs to be specified in the namelist.wps as:
• max_dom = 3
• For each nest you have, you will need to add an extra column for some parameters in your namelist.wps file

Let's try the following activity in order for you to see how nesting works in WPS.

Activity
Open your e-WRF installation and after that, open a Terminal window. Let's now create a new folder called "NEST", where we will be creating working with our experiment. So, here are the commands:

$cd$ cd WRF
$mkdir NEST$ cd NEST

Now, you will also need to copy the WPS files there.

$cp -r ../WPS .$ cd WPS

After that, use gedit and edit your namelist.wps file so that it is exactly like the file represented in the box below.
$gedit namelist.wps namelist.wps using a parent domain and two nests &share wrf_core = 'ARW', max_dom = 3, start_date = '2006-08-16_12:00:00','2006-08-16_12:00:00', end_date = '2006-08-16_18:00:00','2006-08-16_12:00:00', interval_seconds = 21600 io_form_geogrid = 2, / &geogrid parent_id = 1, 1, 2, parent_grid_ratio = 1, 3, 3, i_parent_start = 1, 21, 31, j_parent_start = 1, 21, 31, e_we = 74, 91, 91, e_sn = 61, 91, 91, geog_data_res = '10m','10m','10m', dx = 30000, dy = 30000, map_proj = 'lambert', ref_lat = 60.38, ref_lon = 5.34, truelat1 = 60.38, stand_lon = 5.34, geog_data_path = '/home/climate/WRF/DATA/GEOG' / &ungrib out_format = 'WPS', prefix = 'FILE', / &metgrid fg_name = 'FILE' io_form_metgrid = 2, / After you edited your namelist, do the following: 1. Make a plot of your domain using plotgrids.ncl (see Figure below) 2. Run geogrid.exe 3. After you run geogrid.exe, if your simulation is successful, you should see the words "Successful completion of geogrid." You should also see three new files there (which you can list using the "ls" command) : • geo_em.d01.nc • geo_em.d02.nc • geo_em.d03.nc 4. Each of these three files correspond to the static data for the parent domain (d01) and the two nests (d02 and d03). Use ncview and visualize the static data in these files: •$ ncview geo_em.d01.nc
• $ncview geo_em.d02.nc •$ ncview geo_em.d03.nc

Figure 1 - Plot created for the experiment design using plotgrids.ncl. Here, you can see the parent domain at 30 km resolution (d01), as well as the first nest at 10 km resolution (d02) and the second nest at 3.3 km resolution (d03).

Note: if you have any questions along the way, you can post them on the Facebook group.