Dan, I'm a computer scientist who pretends to know weather modeling, but have done quite a few simulations in the rugged terrain of Alaska. There have been some cases where, with a 1km nest, I've had to start off with sub-second timesteps (I remember going down to 1/20 of a second in one case). It seems like my problems may have been related more to instabilities during initialization, and I was able to kick up the delta_t after a while.<br>
<br>Have you considered adaptive time stepping, whereby you might be able to start at an obscenely small timestep and gradually increase its size? Maybe it's worth your effort (and thousands and thousands of cpu-hours!) to give it a try and see what happens?<br>
<br>There was a discussion in this venue maybe 6 or so months ago, relating to use of the epssm namelist option, though that was more related to dealing with flow over rugged terrain.<br><br>I don't fully understand many of the options you refer to, but in the back of my mind I keep thinking of what was drilled in to me during my School of Hard Knocks days in numerical methods (petroleum engineering back then) - there are all sorts of methods for "smoothing" solutions, allowing for larger timesteps, but sometimes you just gotta get back to basics and try the fine temporal and horizontal resolutions to truly capture the processes you're interested in. But, this is more "opinion" on my part!<br>
<br><div class="gmail_quote">On Sat, Sep 11, 2010 at 10:54 PM, Daniel Steinhoff <span dir="ltr"><<a href="mailto:steinhoff.9@buckeyemail.osu.edu">steinhoff.9@buckeyemail.osu.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Dear wrf-users,<br>
<br>
I am running simulations over the McMurdo Dry Valleys in Antarctica, a region of complex terrain (mountain peaks approaching 4000 m, deep valleys, coastal). In order to properly simulate cold pools and other features in the valleys, I'd like to treat diffusion truly horizontally, as Zangl (2002) did in Alpine simulations with MM5. I've seen in the model documentation and tutorial presentation that diff_opt=2 should only be used with grid spacing < 2 km and without PBL parameterization. Running a 32-8-2 km, 40 vertical levels nested simulation, I'd like to keep the PBL scheme. Has anyone had success using diff_opt=2 for real data cases with a PBL scheme?<br>
<br>
When I try diff_opt=2, with km_opt=2, 3, or 4, the simulations are more sensitive than otherwise to CFL violations or NaN errors at points on steep slopes (this is after extensive terrain smoothing of a 200 m terrain dataset). km_opt=2 runs the longest before crashing (about a half hour), whereas the other options crash within minutes. Interestingly, these CFL violations and NaN errors are more prevalent in the outer grids (for example, either the 32 km or 8 km grids along steep slopes). Might I be better off running the 32 km and 8 km outer grids with diff_opt=1, and then using ndown for an inner grid of 2 km and using diff_opt=2? Or is an extremely short timestep required? I've been down to 60 sec on the 32 km grid. I have similar problems to above with a 27-9-3-1 km nested grid, 51 vertical levels (default spacing) setup also.<br>
<br>
If anyone has any ideas or advice I'd appreciate it. I am running WRF 3.2.1 on NCAR bluefire. I've pasted the namelist below from the 32-8-2 km simulations.<br>
<br>
Dan<br>
<br>
<br>
&time_control<br>
run_days = 0,<br>
run_hours = 60,<br>
run_minutes = 0,<br>
run_seconds = 0,<br>
start_year = 2006, 2006, 2006,<br>
start_month = 04, 04, 04,<br>
start_day = 15, 15, 15,<br>
start_hour = 12, 12, 12,<br>
start_minute = 00, 00, 00,<br>
start_second = 00, 00, 00,<br>
end_year = 2006, 2006, 2006,<br>
end_month = 04, 04, 04,<br>
end_day = 18, 18, 18,<br>
end_hour = 00, 00, 00,<br>
end_minute = 00, 00, 00,<br>
end_second = 00, 00, 00,<br>
interval_seconds = 21600,<br>
input_from_file = .true.,.true.,.true.,<br>
history_interval = 360, 360, 360,<br>
frames_per_outfile = 1, 1, 1,<br>
restart = .False.,<br>
restart_interval = 720,<br>
reset_simulation_start = .false.,<br>
auxinput4_inname = "wrflowinp_d<domain>",<br>
auxinput4_interval = 360, 360, 360,<br>
io_form_history = 2,<br>
auxinput4_interval = 360, 360, 360,<br>
io_form_history = 2,<br>
io_form_restart = 2,<br>
io_form_input = 2,<br>
io_form_boundary = 2,<br>
io_form_auxinput4 = 2,<br>
nocolons = .false.,<br>
debug_level = 0,<br>
auxhist2_outname = "surface_d<domain>_<date>",<br>
auxhist2_interval = 0, 0, 60,<br>
io_form_auxhist2 = 2,<br>
/<br>
<br>
&domains<br>
time_step = 120,<br>
time_step_fract_num = 0,<br>
time_step_fract_den = 1,<br>
max_dom = 3,<br>
e_we = 200, 161, 193,<br>
e_sn = 200, 121, 165,<br>
s_vert = 1, 1, 1,<br>
e_vert = 40, 40, 40,<br>
dx = 32000, 8000, 2000,<br>
dy = 32000, 8000, 2000,<br>
grid_id = 1, 2, 3,<br>
parent_id = 0, 1, 2,<br>
i_parent_start = 1, 68, 54,<br>
parent_id = 0, 1, 2,<br>
i_parent_start = 1, 68, 54,<br>
j_parent_start = 1, 105, 42,<br>
parent_grid_ratio = 1, 4, 4,<br>
parent_time_step_ratio = 1, 4, 4,<br>
feedback = 0,<br>
smooth_option = 0,<br>
num_metgrid_levels = 38,<br>
num_metgrid_soil_levels = 4,<br>
eta_levels = 1.00000 , 0.99629 , 0.99258 , 0.98767 , 0.98275 ,<br>
0.97636 , 0.96996 , 0.96184 , 0.95372 , 0.93357 ,<br>
0.90913 , 0.87957 , 0.84531 , 0.80683 , 0.76467 ,<br>
0.71940 , 0.67163 , 0.62198 , 0.57108 , 0.51956 ,<br>
0.46803 , 0.42030 , 0.37613 , 0.33532 , 0.29764 ,<br>
0.26290 , 0.23092 , 0.20152 , 0.17452 , 0.14978 ,<br>
0.12714 , 0.10646 , 0.08761 , 0.07045 , 0.05466 ,<br>
0.03981 , 0.02580 , 0.01677 , 0.00903 , 0.00000 ,<br>
p_top_requested = 5000,<br>
interp_type = 2,<br>
extrap_type = 2,<br>
t_extrap_type = 2,<br>
use_levels_below_ground = .true.,<br>
use_surface = .true.,<br>
lagrange_order = 1,<br>
lowest_lev_from_sfc = .false.,<br>
smooth_cg_topo = .false.,<br>
force_sfc_in_vinterp = 1,<br>
smooth_cg_topo = .false.,<br>
force_sfc_in_vinterp = 1,<br>
zap_close_levels = 0.,<br>
sfcp_to_sfcp = .false.,<br>
use_adaptive_time_step = .false.,<br>
/<br>
<br>
&dfi_control<br>
/<br>
<br>
&physics<br>
mp_physics = 6, 6, 6,<br>
mp_zero_out = 0,<br>
no_mp_heating = 0,<br>
ra_lw_physics = 1, 1, 1,<br>
ra_sw_physics = 1, 1, 1,<br>
radt = 30, 10, 10,<br>
levsiz = 59,<br>
paerlev = 29,<br>
cam_abs_dim1 = 4,<br>
cam_abs_dim2 = 35,<br>
sf_sfclay_physics = 5, 5, 5,<br>
sf_surface_physics = 2, 2, 2,<br>
sf_urban_physics = 0, 0, 0,<br>
bl_pbl_physics = 5, 5, 5,<br>
bldt = 0, 0, 0,<br>
grav_settling = 1, 1, 1,<br>
bldt = 0, 0, 0,<br>
grav_settling = 1, 1, 1,<br>
cu_physics = 3, 0, 0,<br>
cudt = 5,<br>
cugd_avedx = 1,<br>
isfflx = 1,<br>
ifsnow = 0,<br>
icloud = 1,<br>
swrad_scat = 1.,<br>
surface_input_source = 1,<br>
num_soil_layers = 4,<br>
num_land_cat = 24,<br>
num_soil_cat = 16,<br>
usemonalb = .false.,<br>
rdmaxalb = .false.,<br>
rdlai2d = .false.,<br>
sst_update = 1,<br>
seaice_threshold = 0.0,<br>
tmn_update = 0,<br>
bucket_mm = -1.,<br>
maxiens = 1,<br>
maxens = 3,<br>
maxens2 = 3,<br>
maxens3 = 16,<br>
ensdim = 144,<br>
slope_rad = 1,<br>
topo_shading = 1,<br>
slope_rad = 1,<br>
topo_shading = 1,<br>
shadlen = 25000.,<br>
omlcall = 0,<br>
oml_hml0 = 50.,<br>
oml_gamma = 0.14,<br>
isftcflx = 0,<br>
fractional_seaice = 1,<br>
seaice_thickness = 1,<br>
tice2tsk_if2cold = .true.<br>
/<br>
<br>
&fdda<br>
grid_fdda = 1, 0, 0,<br>
gfdda_inname = "wrffdda_d<domain>",<br>
gfdda_interval_m = 360, 0, 0,<br>
gfdda_end_h = 60, 0, 0,<br>
io_form_gfdda = 2,<br>
fgdt = 0,<br>
if_no_pbl_nudging_uv = 0, 0, 0,<br>
if_no_pbl_nudging_t = 0, 0, 0,<br>
if_no_pbl_nudging_q = 0, 0, 0,<br>
if_zfac_uv = 1, 0, 0,<br>
k_zfac_uv = 13,<br>
if_zfac_t = 1, 0, 0,<br>
k_zfac_t = 13,<br>
if_zfac_q = 1, 0, 0,<br>
k_zfac_t = 13,<br>
if_zfac_q = 1, 0, 0,<br>
k_zfac_q = 40,<br>
guv = 0.0003,0.0000,0.0000,<br>
gt = 0.0003,0.0000,0.0000,<br>
gq = 0.0000,0.0000,0.0000,<br>
if_ramping = 0,<br>
dtramp_min = 60.0,<br>
grid_sfdda = 0, 0, 0,<br>
rinblw = 250.0,<br>
obs_nudge_opt = 0, 0, 0,<br>
/<br>
<br>
&scm<br>
/<br>
<br>
&dynamics<br>
rk_ord = 3,<br>
diff_opt = 2,<br>
km_opt = 2,<br>
diff_6th_opt = 1, 1, 1,<br>
diff_6th_factor = 0.06, 0.06, 0.06,<br>
damp_opt = 3,<br>
zdamp = 5000., 5000., 5000.,<br>
dampcoef = 0.03, 0.03, 0.03,<br>
w_damping = 0,<br>
base_temp = 268.,<br>
w_damping = 0,<br>
base_temp = 268.,<br>
base_pres = 100000.,<br>
base_lapse = 50.,<br>
khdif = 0, 0, 0,<br>
kvdif = 0, 0, 0,<br>
smdiv = 0.1, 0.1, 0.1,<br>
emdiv = 0.01, 0.01, 0.01,<br>
epssm = 0.1, 0.1, 0.1,<br>
non_hydrostatic = .true., .true., .true.,<br>
h_mom_adv_order = 5, 5, 5,<br>
v_mom_adv_order = 3, 3, 3,<br>
h_sca_adv_order = 5, 5, 5,<br>
v_sca_adv_order = 3, 3, 3,<br>
time_step_sound = 4, 4, 4,<br>
moist_adv_opt = 1, 1, 1,<br>
scalar_adv_opt = 1, 1, 1,<br>
tke_adv_opt = 1, 1, 1,<br>
gwd_opt = 0,<br>
/<br>
<br>
&bdy_control<br>
spec_bdy_width = 5,<br>
spec_zone = 1,<br>
relax_zone = 4,<br>
specified = .true., .false.,.false.,<br>
spec_exp = 0.,<br>
specified = .true., .false.,.false.,<br>
spec_exp = 0.,<br>
periodic_x = .false.,.false.,.false.,<br>
symmetric_xs = .false.,.false.,.false.,<br>
symmetric_xe = .false.,.false.,.false.,<br>
open_xs = .false.,.false.,.false.,<br>
open_xe = .false.,.false.,.false.,<br>
periodic_y = .false.,.false.,.false.,<br>
symmetric_ys = .false.,.false.,.false.,<br>
symmetric_ye = .false.,.false.,.false.,<br>
open_ys = .false.,.false.,.false.,<br>
open_ye = .false.,.false.,.false.,<br>
nested = .false.,.true.,.true.,<br>
/<br>
<br>
&grib2<br>
/<br>
<br>
&tc<br>
/<br>
<br>
&fire<br>
/<br>
<br>
&namelist_quilt<br>
nio_tasks_per_group = 0,<br>
nio_groups = 1,<br>
201,2 99%<br>
nio_tasks_per_group = 0,<br>
nio_groups = 1,<br>
/<br>
<br>
<br>
Daniel Steinhoff<br>
Polar Meteorology Group<br>
Byrd Polar Research Center<br>
The Ohio State University<br>
<a href="mailto:steinhoff.9@buckeyemail.osu.edu">steinhoff.9@buckeyemail.osu.edu</a><br>
<br>
<br>
<br>
<br>
<br>
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</blockquote></div><br><br clear="all"><br>-- <br>Arctic Region Supercomputing Center<br><a href="http://weather.arsc.edu/" target="_blank">http://weather.arsc.edu/</a><div><a href="http://www.arsc.edu/%7Emorton/" target="_blank">http://www.arsc.edu/~morton/</a></div>
<br>