GFS sfc_diff Main

This subroutine calculates surface roughness length. More...

Detailed Description

Argument Table

local_name	standard_name	long_name	units	rank	type	kind	intent	optional
im	horizontal_loop_extent	horizontal loop extent	count	0	integer		in	F
ps	surface_air_pressure	surface pressure	Pa	1	real	kind_phys	in	F
u1	x_wind_at_lowest_model_layer	x component of 1st model layer wind	m s-1	1	real	kind_phys	in	F
v1	y_wind_at_lowest_model_layer	y component of 1st model layer wind	m s-1	1	real	kind_phys	in	F
t1	air_temperature_at_lowest_model_layer	1st model layer air temperature	K	1	real	kind_phys	in	F
q1	specific_humidity_at_lowest_model_layer	1st model layer specific humidity	kg kg-1	1	real	kind_phys	in	F
z1	height_above_mean_sea_level_at_lowest_model_layer	height above mean sea level at 1st model layer	m	1	real	kind_phys	in	F
snwdph	surface_snow_thickness_water_equivalent	water equivalent surface snow thickness	mm	1	real	kind_phys	in	F
tskin	surface_skin_temperature	surface skin temperature	K	1	real	kind_phys	in	F
z0rl	surface_roughness_length	surface roughness length	cm	1	real	kind_phys	inout	F
cm	surface_drag_coefficient_for_momentum_in_air	surface exchange coeff for momentum	none	1	real	kind_phys	inout	F
ch	surface_drag_coefficient_for_heat_and_moisture_in_air	surface exchange coeff heat & moisture	none	1	real	kind_phys	inout	F
rb	bulk_richardson_number_at_lowest_model_level	bulk Richardson number at the surface	none	1	real	kind_phys	inout	F
prsl1	air_pressure_at_lowest_model_layer	Model layer 1 mean pressure	Pa	1	real	kind_phys	in	F
prslki	ratio_of_exner_function_between_midlayer_and_interface_at_lowest_model_layer	Exner function ratio bt midlayer and interface at 1st layer	ratio	1	real	kind_phys	in	F
islimsk	sea_land_ice_mask	landmask: sea/land/ice=0/1/2	flag	1	integer		in	F
stress	surface_wind_stress	surface wind stress	m2 s-2	1	real	kind_phys	inout	F
fm	Monin-Obukhov_similarity_function_for_momentum	Monin-Obukhov similarity parameter for momentum	none	1	real	kind_phys	inout	F
fh	Monin-Obukhov_similarity_function_for_heat	Monin-Obukhov similarity parameter for heat	none	1	real	kind_phys	inout	F
ustar	surface_friction_velocity	surface friction velocity	m s-1	1	real	kind_phys	inout	F
wind	wind_speed_at_lowest_model_layer	wind speed at lowest model level	m s-1	1	real	kind_phys	inout	F
ddvel	surface_wind_enhancement_due_to_convection	surface wind enhancement due to convection	m s-1	1	real	kind_phys	in	F
fm10	Monin-Obukhov_similarity_function_for_momentum_at_10m	Monin-Obukhov similarity parameter for momentum	none	1	real	kind_phys	inout	F
fh2	Monin-Obukhov_similarity_function_for_heat_at_2m	Monin-Obukhov similarity parameter for heat	none	1	real	kind_phys	inout	F
sigmaf	vegetation_area_fraction	areal fractional cover of green vegetation	frac	1	real	kind_phys	in	F
vegtype	cell_vegetation_type	vegetation type at each grid cell	index	1	integer		in	F
shdmax	maximum_vegetation_area_fraction	max fractnl cover of green veg	frac	1	real	kind_phys	in	F
ivegsrc	vegetation_type	vegetation type data source umd or igbp	index	0	integer		in	F
tsurf	surface_skin_temperature_after_iteration	surface skin temperature after iteration	K	1	real	kind_phys	in	F
flag_iter	flag_for_iteration	flag for iteration	flag	1	logical		in	F
redrag	flag_for_reduced_drag_coefficient_over_sea	flag for reduced drag coefficient over sea	flag	0	logical		in	F
errmsg	error_message	error message for error handling in CCPP	none	0	character	len=*	out	F
errflg	error_flag	error flag for error handling in CCPP	flag	0	integer		out	F

GFS Surface Layer Scheme General Algorithm

1. Calculate the thermal roughness length formulation over the ocean (see eq. (25) and (26) in [88]).
2. Calculate Zeng's momentum roughness length formulation over land and sea ice.
3. Calculate the new vegetation-dependent formulation of thermal roughness length ([91]). [91] proposed a new formulation on \(ln(Z_{0m}^,/Z_{0t})\) as follows:

   \[ ln(Z_{0m}^,/Z_{0t})=(1-GVF)^2C_{zil}k(u*Z_{0g}/\nu)^{0.5} \]

   where \(Z_{0m}^,\) is the effective momentum roughness length computed in the following equation for each grid, \(Z_{0t}\) is the roughness lenghth for heat, \(C_{zil}\) is a coefficient (taken as 0.8), k is the Von Karman constant (0.4), \(\nu=1.5\times10^{-5}m^{2}s^{-1}\) is the molecular viscosity, \(u*\) is the friction velocity, and \(Z_{0g}\) is the bare soil roughness length for momentum (taken as 0.01).
   In order to consider the convergence of \(Z_{0m}\) between fully vegetated and bare soil, the effective \(Z_{0m}^,\) is computed:

   \[ \ln(Z_{0m}^,)=(1-GVF)^{2}\ln(Z_{0g})+\left[1-(1-GVF)^{2}\right]\ln(Z_{0m}) \]

4. Calculate the exchange coefficients: \(cm\), \(ch\), and \(stress\) as inputs of other sfc schemes.

Detailed Algorithm

Functions/Subroutines
subroutine	sfc_ex_coef::sfc_ex_coef_run (im, ps, u1, v1, t1, q1, z1, snwdph, tskin, z0rl, cm, ch, rb, prsl1, prslki, islimsk, stress, fm, fh, ustar, wind, ddvel, fm10, fh2, sigmaf, vegtype, shdmax, ivegsrc, tsurf, flag_iter, redrag, errmsg, errflg )