Vortex-Following Exercise

Vortex-following Option

A WRF configuration that tracks the center of low pressure in a tropical cyclone, and allows the nested domain to move inside the parent to follow the cyclone as it moves.

Tropical cyclones often move across a large area, and when simulating them, a large, high-resolution domain can be computationally expensive. The Vortex Following option uses a large static coarse parent domain, with a nest that moves with the center of low pressure in a tropical cyclone. To use this option, WRF must be compiled with the “vortex-following” nest option, but it uses standard WPS.

Note

The Vortex-following capability only works for tracking cyclones.

Set-up WPS

Important

To avoid overwriting files from other exercises, create a dedicated directory to store the geo_em*, met_em*, ungrib output, and namelist.wps.

1. Move to the /glade/derecho/scratch/$USER/practice_exercises/wps directory.

   
   

2. Use the following information to modify namelist.wps:

   • Case : Hurricane Matthew, which made landfall as a category 4 hurricane over Haiti, and then weakened before hitting the U.S. coast of South Carolina.

   • Dates: 2016-10-06_00:00:00 to 2016-10-08_00:00:00

   • Although you will ultimately process two domains (one parent and one nest), for the WPS process, only configure the parent domain - the only static domain.

   • Domain size : 91 x 100 grid points

   • Grid resolution : 27 km

   • Map projection: mercator - the recommended projection when closer to the equator

   • To place the domain in the right location on the Earth, make the following additional namelist changes:

     
     

     ref_lat = 28.00
     ref_lon = -75.00
     truelat1 = 28.0,
     stand_lon = -75.00
     

   
   
   
   

3. The following pertains to the meteorological input data:

   Type	Global NCEP GFS
   Interval	Every 3 hours
   Initial Time	2016-10-06_00:00:00
   End Time	2016-10-08_00:00:00
   Data Directory	/glade/campaign/mmm/wmr/wrf_tutorial/input_data/climate/
   File Root	gfs.0p25.2016100600.f0
   Vtable	Vtable.GFS

   
   
   
   

4. Check the domain’s location, which should be similar to the below image:

   

   
   
   
   

5. Run the WPS executables to create input files for wrf.

   
   

   Note

   Because this case uses a lot of data, NCAR’s HPC system MAY give a segmentation fault when running it with the standard command (./ungrib.exe) if the login nodes become saturated. To avoid this, use the following (where UMMM0013 is this class’s computing project):

   
   

   qcmd -A UMMM0013 -- ./ungrib.exe
   

Set-up and Run WRF

1. Move to the /glade/derecho/scratch/$USER/practice_exercises/wrf_vortex/test/em_real directory.

   
   

2. Modify namelist.input to include settings for the static parent domain, and the moving nest (see below), as well as the appropriate dates/times. Domain 01 values should match those from WPS for d01.

   
   

   &time_control
   input_from_file = .true.,.false.,
   interval_seconds = 21600
   
   &domains
   time_step = 150,
   max_dom = 2,
   e_we = 91, 88,
   e_sn = 100, 79,
   num_metgrid_levels = 32
   dx = 27000
   dy = 27000
   i_parent_start = 1, 25,
   j_parent_start = 1, 14,
   parent_grid_ratio = 1, 3,
   parent_time_step_ratio = 1, 3,
   

   
   

   Note

   • No wrfinput_d02 file will be created since input_from_file is set to .false. for domain 2. This is standard for vortex-following runs.

   • The d01 **_parent_start* values represent the initial nest location.

   
   
   
   

3. Run real and wrf.

   
   

4. Check your output.

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