WRF - extreme wind speeds in mountains

[Z Grajek]

Hi, I'm struggling with simulating extreme wind in a mountainous terrain. Below is a graph of wind speed at the mountain station vs. the model. The model couldn't cope with the speed drops towards the end of the simulation. These are results from a 300-meter domain. I've attached the nameless.input I used. Does anyone have any advice on how to manage wind speeds in the mountains? Any tips? Best regards Zosia


&domains
time_step = 4,

max_dom = 3,

e_we = 310, 265, 491,
e_sn = 330, 331, 721,
i_parent_start = 1, 115, 100,
j_parent_start = 1, 130, 114,
e_vert = 70, 70, 70,
auto_levels_opt = 2,
dzbot = 10.0,
dzstretch_s = 1.1,
dzstretch_u = 1.1,

p_top_requested = 5000,
num_metgrid_levels = 38,
num_metgrid_soil_levels = 4,
dx = 4500,
dy = 4500,
grid_id = 1, 2, 3,
parent_id = 1, 1, 2,
parent_grid_ratio = 1, 3, 5,
parent_time_step_ratio = 1, 3, 5,
feedback = 1,
smooth_option = 1,
numtiles = 4,
smooth_cg_topo = .false.,

nproc_x = 16
nproc_y = 16
/

&physics
mp_physics = 8, 8, 8,
ra_lw_physics = 4, 4, 4,
ra_sw_physics = 4, 4, 4,
radt = 3, 3, 3,
sf_sfclay_physics = 5, 5, 5,
sf_surface_physics = 2, 2, 2,
num_soil_layers = 4,
bl_pbl_physics = 5, 5, 5,
bldt = 0, 0, 0,
cu_physics = 0, 0, 0,
cudt = 0, 0, 0,
isfflx = 1,
ifsnow = 1,
icloud = 1,
surface_input_source = 3,
num_land_cat = 21,
sf_urban_physics = 0, 0, 0,
bl_mynn_edmf = 1, 1, 1,
bl_mynn_edmf_tke = 1, 1, 1,
bl_mynn_tkeadvect = .true., .true., .true.,
/

&fdda
/

&dynamics
hybrid_opt = 2,
non_hydrostatic = .true., .true., .true.,
w_damping = 1,
damp_opt = 3,
zdamp = 5000., 5000., 5000.,
dampcoef = 0.2, 0.2, 0.2,
diff_opt = 2, 2, 2,
km_opt = 4, 4, 4,
diff_6th_opt = 2, 2, 2,
diff_6th_factor = 0.02,
epssm = 0.6, 0.6, 0.6,
base_temp = 290.,
moist_adv_opt = 1, 1, 1,
scalar_adv_opt = 1, 1, 1,
gwd_opt = 0, 0, 0,
/

 

[Ming Chen]

Your namelist.input looks fine to me except that:

(1) time step can be larger. For dx=4.5km, max time_step can be 27s
(2) it may be better to run this case with the SMS-3DTKE scale-adaptive LES/PBL scheme
(3) Please turn on the option topo_wind, which may be helpful to yield better surface winds

Hope this is helpful. Surface wind simulation is always a challenging issue in WRF studies. I know that some people develop post-process tools to correct bias in their simulations.

By the way, how did you match model results with your station observations? Did you interpolate model data to station sites? if so, how did you do ?

Please let me know if you have more questions.

 

[meteoadriatic]

(3) Please turn on the option topo_wind, which may be helpful to yield better surface winds

Ming, does topo_wind do anything outside of YSU PBL?

Ivan

 

[Ming Chen]

Hi Ivan,

You are right that topo_wind only works with YSU PBL. Sorry that I forgot this prerequisite for using this option.

Ming