Bottom_top dimension in WRF output

[utkarsh-7]

Hi,
I am running WRF model simulation and not sure that which namelist configuration is actually affecting the bottom_top dimension in wrf output?

For the same lat,long I am getting output at 32 different levels. But I do not need 32 levels for a single lat/long(only 2-3 would be enough for me).
Is there a way to reduce these levels in the output?
Also by reducing the levels will it affect the running time of the model?
namelist.wps -

&share
nocolons = .true.
max_dom = 2
start_date = '2023-06-05_00:00:00', '2023-06-05_00:00:00'
end_date = '2023-06-05_01:00:00', '2023-06-05_01:00:00'
interval_seconds = 3600
/

&geogrid
parent_id = 1, 1
parent_grid_ratio = 1, 2
i_parent_start = 1, 11
j_parent_start = 1, 11
e_we = 31, 31
e_sn = 31, 31
map_proj = 'lambert'
dx = 6000
dy = 6000
ref_lon = -74.50
ref_lat = 41.50
geog_data_res = 'lowres', 'lowres'
geog_data_path = '/wrf_32/DATA/geog/WPS_GEOG_LOW_RES'
truelat1 = 30.0
truelat2 = 60.0
stand_lon = -74.50
/

&ungrib
out_format = 'WPS',
prefix = 'FILE',
pmin = 1.
/

&metgrid
fg_name = 'FILE'
/

namelist.input -

&time_control
start_year = 2023, 2023
start_month = 6, 6
start_day = 05, 05
start_hour = 00, 00
end_year = 2023, 2023
end_month = 6, 6
end_day = 05, 05
end_hour = 01, 01
interval_seconds = 3600
input_from_file = .true., .true.
history_interval = 60, 60
frames_per_outfile = 100, 100
restart = .false.
restart_interval = 7200
io_form_history = 2
io_form_restart = 2
io_form_input = 2
io_form_boundary = 2
start_minute = 0, 0
start_second = 0, 0
end_minute = 0, 0
end_second = 0, 0
nocolons = .true.
/

&domains
time_step = 36
time_step_fract_num = 0
time_step_fract_den = 1
max_dom = 2
e_we = 31, 31
e_sn = 31, 31
e_vert = 33, 33
num_metgrid_levels = 42
num_metgrid_soil_levels = 4
dx = 6000.0,
dy = 6000.0,
grid_id = 1, 2
parent_id = 1, 1
i_parent_start = 1, 11
j_parent_start = 1, 11
parent_grid_ratio = 1, 2
parent_time_step_ratio = 1, 2
feedback = 1
smooth_option = 0
sfcp_to_sfcp = .true.
/

&physics
physics_suite = 'CONUS'
mp_physics = 0, 0
cu_physics = 0, 0
radt = 9, 3
bldt = 0, 0
cudt = 0, 0
icloud = 0
num_land_cat = 21
sf_urban_physics = 1, 1
/

&dynamics
hybrid_opt = 2
w_damping = 0
diff_opt = 1, 1
km_opt = 4, 4
diff_6th_opt = 0, 0
diff_6th_factor = 0.12, 0.12
base_temp = 290.0
damp_opt = 3
zdamp = 5000.0, 5000.0
dampcoef = 0.2, 0.2
khdif = 0, 0
kvdif = 0, 0
/

&bdy_control
spec_bdy_width = 5
specified = .true.
/

&namelist_quilt
/

 

[kwerner]

It's likely you actually have 33 levels, but they start with level 0. This number is based on the number of atmospheric levels that are in your input, first-guess data (e.g., GFS data). Setting num_metgrid_levels = 33 lets the real.exe program know you are using input data with 33 levels. You cannot reduce that value because it needs to match the number of levels detected in the met_em* files. Furthermore, running with only 2-3 levels would cause the model to crash because it wouldn't be realistic.

 

[utkarsh-7]

Thanks you but just another follow up question -
So how many levels you would suggest to keep? Because I am only interested in the data near the surface so from the performance perspective, I was trying to reduce the levels.

 

[kwerner]

I would suggest keeping all the levels the data comes with. If you remove levels, the data is not going to be reasonable.