<div dir="ltr">Those dreaded CFL errors! We all feel your pain.<div><br><div>Having them that bad in a North American domain makes me think you have undesirable input data for the initialization. You already tried shorter time steps, try an earlier start time (8 hours maybe) as a test. </div><div><br></div><div>I'm over simplifying, but CFL errors mean you have too much vertical velocity for the height of your grid cells. Having mountains near your domain boundaries make this happen more often. But with a continental domain, your corners are probably over the ocean. Maybe the input has strangely warm water causing vertical velocities. Sometimes just changing the eppsm value (read your WRF namelist documentation) from 0.1 to 0.3, or anything else BELOW 1.0, will magically fix the problem. If this was not happening immediately after the start, I would suggest adding some vertical dampening. I have longer versions of these ideas here: <a href="http://www.nusculus.com/wrf-errors">http://www.nusculus.com/wrf-errors</a> </div><div>I'm sorry to not have any absolute answers but maybe this will give you something else to try.<br></div><div><br></div><div>best wishes</div><div>Kevin</div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Mar 30, 2016 at 8:04 PM, Wang, Yaoping <span dir="ltr"><<a href="mailto:wang.3866@buckeyemail.osu.edu" target="_blank">wang.3866@buckeyemail.osu.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
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<p>Hello, </p>
<p><br>
</p>
<div style="color:rgb(0,0,0)">
<div>
<div style="color:rgb(0,0,0);font-family:"Times New Roman",Times,serif;font-size:12pt;background-color:rgb(255,255,255)">
<p>I am new to WRF and am setting up a run over the North American domain at 30km resolution. But I keep getting "exceeded cfl=2". After testing various time steps it seems that the error keep occurring at the corners of my domain. I also checked the wind speeds
and divergence in the input meteorological data, but did not find any clear outlier models. Could anyone give some suggestions as to what can be done to solve the problem?
</p>
<p><br>
</p>
<p><u>The trials and errors: </u></p>
<p><strong>time step = 180s</strong></p>
<p>d01 1967-01-01_00:00:00 5537 points exceeded cfl=2 in domain d01 at time 1967-01-01_00:00:00 hours<br>
d01 1967-01-01_00:00:00 MAX AT i,j,k: 283 42 2 vert_cfl,w,d(eta)= 2.4396536E+07 NaN 9.9999905E-03<br>
d01 1967-01-01_00:00:00 1906 points exceeded cfl=2 in domain d01 at time 1967-01-01_00:00:00 hours<br>
d01 1967-01-01_00:00:00 MAX AT i,j,k: 21 190 20 vert_cfl,w,d(eta)= 1102.228 -6444.851 3.5938144E-02<br>
Timing for main: time 1967-01-01_00:03:00 on domain 1: 15.48090 elapsed seconds<br>
</p>
<p><br>
</p>
<p><strong>time step = 90s</strong></p>
<p>d01 1967-01-01_00:00:00 6080 points exceeded cfl=2 in domain d01 at time 1967-01-01_00:00:00 hours<br>
d01 1967-01-01_00:00:00 MAX AT i,j,k: 283 46 29 vert_cfl,w,d(eta)= 6955.001 -1.8047905E+15 9.2214663E-03<br>
d01 1967-01-01_00:00:00 1969 points exceeded cfl=2 in domain d01 at time 1967-01-01_00:00:00 hours<br>
d01 1967-01-01_00:00:00 MAX AT i,j,k: 278 56 21 vert_cfl,w,d(eta)= 2879.670 56544.66 3.2001421E-02<br>
Timing for main: time 1967-01-01_00:01:30 on domain 1: 13.09157 elapsed seconds<br>
</p>
<p><br>
</p>
<p><strong>time step = 30s<strong>, namelist.input &domains smooth_cg_topo = .true.</strong></strong></p>
<p>d01 1967-01-01_00:00:00 5537 points exceeded cfl=2 in domain d01 at time 1967-01-01_00:00:00 hours<br>
d01 1967-01-01_00:00:00 MAX AT i,j,k: 283 42 2 vert_cfl,w,d(eta)= 2.4396536E+07 NaN 9.9999905E-03<br>
d01 1967-01-01_00:00:00 1906 points exceeded cfl=2 in domain d01 at time 1967-01-01_00:00:00 hours<br>
d01 1967-01-01_00:00:00 MAX AT i,j,k: 21 190 20 vert_cfl,w,d(eta)= 1102.228 -6444.851 3.5938144E-02<br>
</p>
<p><br>
</p>
<p><strong>time step = 10s, namelist.input &domains smooth_cg_topo = .true.<br>
</strong></p>
<p>d01 1967-01-01_00:00:00 2548 points exceeded cfl=2 in domain d01 at time 1967-01-01_00:00:00 hours<br>
d01 1967-01-01_00:00:00 MAX AT i,j,k: 285 179 23 vert_cfl,w,d(eta)= 8.4951393E+14 2.3136813E+23 2.4293438E-02<br>
d01 1967-01-01_00:00:00 987 points exceeded cfl=2 in domain d01 at time 1967-01-01_00:00:00 hours<br>
d01 1967-01-01_00:00:00 MAX AT i,j,k: 285 196 14 vert_cfl,w,d(eta)= 24310.53 372558.9 6.8435431E-02<br>
Timing for main: time 1967-01-01_00:00:10 on domain 1: 15.84628 elapsed seconds<br>
</p>
<p><u><br>
</u></p>
<p><u>The namelist.input file: </u></p>
<p></p>
<blockquote style="margin-right:0px" dir="ltr">
<p> &time_control<br>
run_days = 3,<br>
run_hours = 0,<br>
run_minutes = 0,<br>
run_seconds = 0,<br>
start_year = 1967,<br>
start_month = 01,<br>
start_day = 01,<br>
start_hour = 00,<br>
start_minute = 00,<br>
start_second = 00,<br>
end_year = 1967,<br>
end_month = 01,<br>
end_day = 04,<br>
end_hour = 00,<br>
end_minute = 00,<br>
end_second = 00,<br>
interval_seconds = 21600<br>
input_from_file = .true.<br>
history_interval = 60, <br>
frames_per_outfile = 1000,<br>
restart = .false.,<br>
restart_interval = 5000,<br>
io_form_history = 2<br>
io_form_restart = 2<br>
io_form_input = 2<br>
io_form_boundary = 2<br>
debug_level = 0<br>
/</p>
<p> &domains<br>
time_step = 10,<br>
time_step_fract_num = 0,<br>
time_step_fract_den = 1,<br>
max_dom = 1,<br>
s_we = 1,<br>
s_sn = 1,<br>
s_vert = 1,<br>
e_we = 290,<br>
e_sn = 200,<br>
e_vert = 30,<br>
p_top_requested = 5000,<br>
num_metgrid_levels = 27,<br>
num_metgrid_soil_levels = 4,<br>
dx = 30000,<br>
dy = 30000,<br>
grid_id = 1,<br>
parent_id = 1,<br>
i_parent_start = 1,<br>
j_parent_start = 1,<br>
smooth_option = 0<br>
smooth_cg_topo = .true.<br>
/</p>
<p> &physics<br>
mp_physics = 3,<br>
ra_lw_physics = 1,<br>
ra_sw_physics = 1,<br>
radt = 30,<br>
sf_sfclay_physics = 1,<br>
sf_surface_physics = 2,<br>
bl_pbl_physics = 1,<br>
bldt = 0,<br>
cu_physics = 1,<br>
cudt = 5,<br>
isfflx = 1,<br>
ifsnow = 1,<br>
icloud = 1,<br>
surface_input_source = 1,<br>
num_soil_layers = 4,<br>
sf_urban_physics = 0,<br>
/</p>
<p> &fdda<br>
/</p>
<p> &dynamics<br>
w_damping = 0,<br>
diff_opt = 1,<br>
km_opt = 4,<br>
diff_6th_opt = 0,<br>
diff_6th_factor = 0.12,<br>
base_temp = 290.<br>
damp_opt = 0,<br>
zdamp = 5000.,<br>
dampcoef = 0.2,<br>
khdif = 0,<br>
kvdif = 0,<br>
non_hydrostatic = .true.,<br>
moist_adv_opt = 1,<br>
scalar_adv_opt = 1,<br>
/</p>
<p> &bdy_control<br>
spec_bdy_width = 5,<br>
spec_zone = 1,<br>
relax_zone = 5,<br>
specified = .true.,<br>
nested = .false.,<br>
/</p>
<p> &grib2<br>
/</p>
<p> &namelist_quilt<br>
nio_tasks_per_group = 0,<br>
nio_groups = 1,<br>
/<br>
</p>
</blockquote>
<p><br>
</p>
<p>Thank you very much, </p>
<p>Yaoping Wang</p>
<div><br>
</div>
</div>
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