[Wrf-users] Fwd: two way nest run crashes without errors

Mon Jun 9 15:46:54 MDT 2014

For a 1km domain, a time step of 10s is too large. The rule of thumb is the time step should be no larger than 6*dx where dx is in km, and sometimes the time step has to be smaller than 6*dx or the model will become unstable. In general, it's a good idea to set parent_time_step_ratio to be the same as parent_grid_ratio, except possibly for some special cases. 

----- Original Message -----
From: "Xin Xi" <xxi at gatech.edu> 
To: "Eric Altshuler" <ela at cola.iges.org> 
Cc: wrf-users at ucar.edu 
Sent: Monday, June 9, 2014 4:43:06 PM 
Subject: Re: [Wrf-users] Fwd: two way nest run crashes without errors 

Thanks Eric! I will look into using 3 nests. 
Just to clarify, if I use time step of 60sec for parent domain and parent_time_step_ratio of 6, the nest domain will run at 10sec, correct? I suspect a small time step (like 10 sec) is needed for such fine resolution domain (e.g. 1km). Why did you say that would make the time step too large on the nest domain? 

On Mon, Jun 9, 2014 at 1:10 PM, Eric Altshuler < ela at cola.iges.org > wrote: 

I would think a nest grid ratio of 15 is too large. The recommended value is 3, and 5 can also be used. Also, your time step ratio is 6, which would probably make the time step too large on your nest domain with a grid ratio of 15. You need to use a triple nest if your high resolution domain is 1 km. One suggestion might be: 

dx = 15000, 5000, 1000 
dy = 15000, 5000, 1000 
parent_grid_ratio = 1, 3, 5 
parent_time_step_ratio = 1, 3, 5 

or: 

dx = 15000, 3000, 1000 
dy = 15000, 3000, 1000 
parent_grid_ratio = 1, 5, 3 
parent_time_step_ratio = 1, 5, 3 

I'm not sure which one is preferable. 

Best regards, 

Eric L. Altshuler 
Research Scientist 
Center for Ocean-Land-Atmosphere Studies 
253 Research Hall, Mail Stop 6C5 
George Mason University 
4400 University Drive 
Fairfax, VA 22030 USA 

E-mail: ela at cola.iges.org 
Phone: (703) 993-5725 
Fax: (703) 993-5770 

From: "Xin Xi" < xxi at gatech.edu > 
To: wrf-users at ucar.edu 
Sent: Monday, June 9, 2014 11:12:26 AM 
Subject: [Wrf-users] Fwd: two way nest run crashes without errors 

Hi I am running wrf 3.6 with two way nesting. After the spinning up on outer domain, the program stopped without any warning or errors. in other words, the program simply stopped at the beginning of the nest domain start time. I wonder whether this is an issue of parent_grid_ratio (=15), time step or the vertical lvls. Please help. Thanks. 

Here is excerpt of namelist.input: 

&time_control 
run_days = 3, 
run_hours = 13, 
run_minutes = 0, 
run_seconds = 0, 
start_year = 2013, 2013, 2000, 
start_month = 03, 03, 01, 
start_day = 10, 11, 24, 
start_hour = 12, 00, 12, 
start_minute = 00, 00, 00, 
start_second = 00, 00, 00, 
end_year = 2013, 2013, 2000, 
end_month = 03, 03, 01, 
end_day = 14, 14, 25, 
end_hour = 00, 00, 12, 
end_minute = 00, 00, 00, 
end_second = 00, 00, 00, 
interval_seconds = 21600 
input_from_file = .true.,.true.,.true., 
history_interval = 60, 60, 60, 
frames_per_outfile = 24, 24, 1000, 
restart = .false., 
restart_interval = 5000, 
io_form_history = 2 
io_form_restart = 2 
io_form_input = 2 
io_form_boundary = 2 
debug_level = 5000 
fine_input_stream = 0, 2, 2, 
io_form_auxinput2 = 2 
/ 

&domains 
time_step = 60, 
time_step_fract_num = 0, 
time_step_fract_den = 1, 
max_dom = 2, 
e_we = 50, 166, 94, 
e_sn = 50, 166, 91, 
e_vert = 57, 57, 30, 
p_top_requested = 5000, 
num_metgrid_levels = 27, 
num_metgrid_soil_levels = 4, 
dx = 15000, 1000, 3333.33, 
dy = 15000, 1000, 3333.33, 
grid_id = 1, 2, 3, 
parent_id = 0, 1, 2, 
i_parent_start = 1, 20, 30, 
j_parent_start = 1, 20, 30, 
parent_grid_ratio = 1, 15, 3, 
parent_time_step_ratio = 1, 6, 3, 
feedback = 1, 
smooth_option = 0, 
eta_levels = 1.000, 0.999, 0.998, 0.997, 0.996, 0.995, 0.994, 0.993, 
0.991, 0.988, 0.985, 0.982, 0.978, 0.974, 0.970, 0.965, 
0.960, 0.955, 0.950, 0.945, 0.935, 0.925, 0.915, 0.905, 
0.895, 0.875, 0.855, 0.840, 0.820, 0.800, 0.760, 0.720, 
0.680, 0.640, 0.600, 0.575, 0.525, 0.485, 0.445, 0.400, 
0.350, 0.300, 0.285, 0.251, 0.217, 0.192, 0.164, 0.141, 
0.119, 0.103, 0.083, 0.067, 0.055, 0.043, 0.033, 0.024, 
0.000, 

/ 

-- 
Xin Xi 
School of Earth and Atmospheric Sciences 
Georgia Institute of Technology 
311 Ferst Drive, Atlanta, GA 30332-0340 

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-- 
Xin Xi 
School of Earth and Atmospheric Sciences 
Georgia Institute of Technology 
311 Ferst Drive, Atlanta, GA 30332-0340 
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