## running over steep topography, epssm and smoothing

Discuss advection schemes, timestepping, pressure gradients, coordinates, etc.

### running over steep topography, epssm and smoothing

I am trying to run WRF at 1km over a valley in the Himalayas. Due to the extremely steep topography around Everest I am getting a lot of CFL errors.

By setting the epssm to 1, I can run it using a 1*dx timestep. Does anyone know if having the epssm at 1 will affect the results?
http://www2.mmm.ucar.edu/wrf/users/work ... ac_wrf.pdf, and Ikawa 1998 suggest it is OK but I have found some sources suggesting it should only be increased to 0.5 (I cannot run it at all at less than 0.8).

Even with the epssm unfortunately 1*dx is too slow for my purposes (slower than real time) so I am looking for ways to improve this. I can run with a larger timestep but find unrealistic vertical velocity around Everest. I am reluctant to smooth the whole domain, but am considering smoothing just the area over Everest (which is in the middle of the domain far from the boundary). Does anyone know if this is possible using geogrid, or have any other suggestions of dynamics options I can try to improve stability? I've tried using adaptive timestep but it adapts to a slightly smaller timestep.

Full namelist below:

&time_control
run_days = 46,
run_hours = 0,
run_minutes = 0,
run_seconds = 0,
start_year = 2014, 2014, 2014, 2014,
start_month = 06, 06, 06, 06,
start_day = 16, 16, 16, 16,
start_hour = 18, 18, 18, 18,
start_minute = 00, 00, 00, 00,
start_second = 00, 00, 00, 00,
end_year = 2014, 2014, 2014, 2014,
end_month = 07, 07, 07, 07,
end_day = 31, 31, 31, 31,
end_hour = 18, 18, 18, 18,
end_minute = 00, 00, 00, 00,
end_second = 00, 00, 00, 00,
interval_seconds = 21600
input_from_file = .true.,.true.,.true.,.true.
history_interval = 60, 60, 60, 60,
adjust_output_times = .true.,
frames_per_outfile = 168, 168, 168, 168,
restart = .false.,
write_hist_at_0h_rst = .true.,
restart_interval = 1440,
io_form_history = 2
io_form_restart = 2
io_form_input = 2
io_form_boundary = 2
debug_level = 1
/

&domains
time_step = 27,
time_step_fract_num = 0,
time_step_fract_den = 1,
max_dom = 4,
e_we = 151, 151, 151, 130,
e_sn = 151, 151, 151, 130,
e_vert = 50, 50, 50, 50,
p_top_requested = 5000,
num_metgrid_levels = 38,
num_metgrid_soil_levels = 4,
dx = 27000, 9000, 3000, 1000,
dy = 27000, 9000, 3000, 1000,
grid_id = 1, 2, 3, 4,
parent_id = 0, 1, 2, 3,
i_parent_start = 1, 51, 51, 54,
j_parent_start = 1, 51, 51, 54,
parent_grid_ratio = 1, 3, 3, 3,
parent_time_step_ratio = 1, 3, 3, 3,
feedback = 0,
smooth_option = 0
use_adaptive_time_step = .false.
step_to_output_time = .true.
target_cfl = 1.5, 1.5, 1.5, 1.5,
target_hcfl = 1.0, 1.0, 1.0, 1.0,
max_step_increase_pct = 5, 5, 5, 5,
starting_time_step = 27, 9, 3, 1,
max_time_step = -1
min_time_step = 27, 9, 3, 1,
adaptation_domain = 4,

/

&physics
mp_physics = 10, 10, 10, 10,
ra_lw_physics = 3, 3, 3, 3,
ra_sw_physics = 3, 3, 3, 3,
radt = 27, 27, 27, 27,
sf_sfclay_physics = 1, 1, 1, 1,
sf_surface_physics = 4, 4, 4, 4,
bl_pbl_physics = 5, 5, 5, 5,
bldt = 0, 0, 0, 0,
cu_physics = 1, 1, 0, 0,
cudt = 0, 0, 0, 0,
isfflx = 1,
ifsnow = 1,
icloud = 1,
surface_input_source = 3,
num_soil_layers = 4,
sf_urban_physics = 0, 0, 0, 0,
slope_rad = 1,
topo_shading = 1,
num_land_cat = 24,
/

&fdda
/

&dynamics
w_damping = 0,
diff_opt = 2, 2, 2, 2,
km_opt = 4, 4, 4, 4,
diff_6th_opt = 2, 2, 2, 2,
diff_6th_factor = 0.12, 0.12, 0.12, 0.12,
base_temp = 290.
damp_opt = 3,
zdamp = 5000., 5000., 5000., 5000.,
dampcoef = 0.2, 0.2, 0.2 0.2,
khdif = 0, 0, 0, 0,
kvdif = 0, 0, 0, 0,
non_hydrostatic = .true., .true., .true., .true.,
moist_adv_opt = 1, 1, 1, 1,
scalar_adv_opt = 1, 1, 1, 1,
epssm = 1.0, 1.0, 1.0, 1.0,
mix_full_fields = .true., .true., .true., .true.,
/

&bdy_control
spec_bdy_width = 5,
spec_zone = 1,
relax_zone = 4,
specified = .true., .false.,.false.,.false.,
nested = .false., .true., .true.,.true.,
/

&grib2
/

&namelist_quilt
nio_tasks_per_group = 0,
nio_groups = 1,
/

-- INSERT --
emilyp

Posts: 10
Joined: Tue Apr 12, 2016 9:14 am

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