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How to derive Specific Humidity from WRF output ?

Alfred-Jose

New member
Hi there, I have been trying to find the variable for Specific Humidity (sph) at single level/ pressure levels from the output files.
Does it come with any specific parameterization schemes.? Although I tried some combinations and have not been able to find it

Thank you so much for your time

PS: Also attaching the list of variables using (WSM6+KF+NOAH+MM5+RRTMG)

File 1 : OUTPUT FROM WRF V4.5.2 MODEL
Descriptor: d02_2013_06_wd.ctl
Binary: d02_2013_06_wd.dat
Type = Gridded
Xsize = 87 Ysize = 54 Zsize = 37 Tsize = 13 Esize = 1
Number of Variables = 113
xlat 1 0 LATITUDE, SOUTH IS NEGATIVE (degree_north)
xlong 1 0 LONGITUDE, WEST IS NEGATIVE (degree_east)
lu_index 1 0 LAND USE CATEGORY (-)
var_sso 1 0 variance of subgrid-scale orography (m2)
u 37 0 x-wind component (m s-1)
v 37 0 y-wind component (m s-1)
w 37 0 z-wind component (m s-1)
ph 37 0 perturbation geopotential (m2 s-2)
phb 37 0 base-state geopotential (m2 s-2)
t 37 0 perturbation potential temperature theta-t0 (K)
thm 37 0 either 1) pert moist pot temp=(1+Rv/Rd Qv)*(theta)-T0, or 2) pert dry pot temp=t (K)
mu 1 0 perturbation dry air mass in column (Pa)
mub 1 0 base state dry air mass in column (Pa)
nest_pos 1 0 - (-)
p 37 0 perturbation pressure (Pa)
pb 37 0 BASE STATE PRESSURE (Pa)
p_hyd 37 0 hydrostatic pressure (Pa)
q2 1 0 QV at 2 M (kg kg-1)
t2 1 0 TEMP at 2 M (K)
th2 1 0 POT TEMP at 2 M (K)
psfc 1 0 SFC PRESSURE (Pa)
u10 1 0 U at 10 M (m s-1)
v10 1 0 V at 10 M (m s-1)
area2d 1 0 Horizontal grid cell area, using dx, dy, and map factors (m2)
dx2d 1 0 Horizontal grid distance: sqrt(area2d) (m)
qvapor 37 0 Water vapor mixing ratio (kg kg-1)
qcloud 37 0 Cloud water mixing ratio (kg kg-1)
qrain 37 0 Rain water mixing ratio (kg kg-1)
shdmax 1 0 ANNUAL MAX VEG FRACTION (-)
shdmin 1 0 ANNUAL MIN VEG FRACTION (-)
snoalb 1 0 ANNUAL MAX SNOW ALBEDO IN FRACTION (-)
tslb 4 0 SOIL TEMPERATURE (K)
smois 4 0 SOIL MOISTURE (m3 m-3)
sh2o 4 0 SOIL LIQUID WATER (m3 m-3)
smcrel 4 0 RELATIVE SOIL MOISTURE (-)
seaice 1 0 SEA ICE FLAG (-)
xicem 1 0 SEA ICE FLAG (PREVIOUS STEP) (-)
sfroff 1 0 SURFACE RUNOFF (mm)
udroff 1 0 UNDERGROUND RUNOFF (mm)
ivgtyp 1 0 DOMINANT VEGETATION CATEGORY (-)
isltyp 1 0 DOMINANT SOIL CATEGORY (-)
vegfra 1 0 VEGETATION FRACTION (-)
grdflx 1 0 GROUND HEAT FLUX (W m-2)
acgrdflx 1 0 ACCUMULATED GROUND HEAT FLUX (J m-2)
acsnom 1 0 ACCUMULATED MELTED SNOW (kg m-2)
snow 1 0 SNOW WATER EQUIVALENT (kg m-2)
snowh 1 0 PHYSICAL SNOW DEPTH (m)
canwat 1 0 CANOPY WATER (kg m-2)
sstsk 1 0 SKIN SEA SURFACE TEMPERATURE (K)
water_dept 1 0 global water depth (m)
coszen 1 0 COS of SOLAR ZENITH ANGLE (dimensionless)
lai 1 0 LEAF AREA INDEX (m-2/m-2)
var 1 0 STANDARD DEVIATION OF SUBGRID-SCALE OROGRAPHY (m)
o3_gfs_du 1 0 Total ozone from GFS (Dobson Units)
mapfac_m 1 0 Map scale factor on mass grid (-)
mapfac_mx 1 0 Map scale factor on mass grid, x direction (-)
mapfac_my 1 0 Map scale factor on mass grid, y direction (-)
mf_vx_inv 1 0 Inverse map scale factor on v-grid, x direction (-)
f 1 0 Coriolis sine latitude term (s-1)
e 1 0 Coriolis cosine latitude term (s-1)
sinalpha 1 0 Local sine of map rotation (-)
cosalpha 1 0 Local cosine of map rotation (-)
hgt 1 0 Terrain Height (m)
tsk 1 0 SURFACE SKIN TEMPERATURE (K)
rainc 1 0 ACCUMULATED TOTAL CUMULUS PRECIPITATION (mm)
rainsh 1 0 ACCUMULATED SHALLOW CUMULUS PRECIPITATION (mm)
rainnc 1 0 ACCUMULATED TOTAL GRID SCALE PRECIPITATION (mm)
snownc 1 0 ACCUMULATED TOTAL GRID SCALE SNOW AND ICE (mm)
graupelnc 1 0 ACCUMULATED TOTAL GRID SCALE GRAUPEL (mm)
hailnc 1 0 ACCUMULATED TOTAL GRID SCALE HAIL (mm)
cldfra 37 0 CLOUD FRACTION (-)
swdown 1 0 DOWNWARD SHORT WAVE FLUX AT GROUND SURFACE (W m-2)
glw 1 0 DOWNWARD LONG WAVE FLUX AT GROUND SURFACE (W m-2)
swnorm 1 0 NORMAL SHORT WAVE FLUX AT GROUND SURFACE (SLOPE-DEPENDENT) (W m-2)
olr 1 0 TOA OUTGOING LONG WAVE (W m-2)
albedo 1 0 ALBEDO (-)
clat 1 0 COMPUTATIONAL GRID LATITUDE, SOUTH IS NEGATIVE (degree_north)
albbck 1 0 BACKGROUND ALBEDO (-)
emiss 1 0 SURFACE EMISSIVITY (-)
noahres 1 0 RESIDUAL OF THE NOAH SURFACE ENERGY BUDGET (W m{-2})
tmn 1 0 SOIL TEMPERATURE AT LOWER BOUNDARY (K)
xland 1 0 LAND MASK (1 FOR LAND, 2 FOR WATER) (-)
ust 1 0 U* IN SIMILARITY THEORY (m s-1)
pblh 1 0 PBL HEIGHT (m)
hfx 1 0 UPWARD HEAT FLUX AT THE SURFACE (W m-2)
qfx 1 0 UPWARD MOISTURE FLUX AT THE SURFACE (kg m-2 s-1)
lh 1 0 LATENT HEAT FLUX AT THE SURFACE (W m-2)
achfx 1 0 ACCUMULATED UPWARD HEAT FLUX AT THE SURFACE (J m-2)
aclhf 1 0 ACCUMULATED UPWARD LATENT HEAT FLUX AT THE SURFACE (J m-2)
snowc 1 0 FLAG INDICATING SNOW COVERAGE (1 FOR SNOW COVER) (-)
sr 1 0 fraction of frozen precipitation (-)
pcb 1 0 base state dry air mass in column (Pa)
pc 1 0 perturbation dry air mass in column (Pa)
landmask 1 0 LAND MASK (1 FOR LAND, 0 FOR WATER) (-)
lakemask 1 0 LAKE MASK (1 FOR LAKE, 0 FOR NON-LAKE) (-)
sst 1 0 SEA SURFACE TEMPERATURE (K)
sst_input 1 0 SEA SURFACE TEMPERATURE FROM WRFLOWINPUT FILE (K)
pressure 37 0 Model pressure (hPa)
height 37 0 Model height (km)
tk 37 0 Temperature (K)
tc 37 0 Temperature (C)
td2 1 0 Dewpoint Temperature at 2m (C)
rh 37 0 Relative Humidity (%)
wspd 37 0 Wind Speed (m s-1)
wdir 37 0 Wind Direction (Degrees)
wd10 1 0 Wind Direction at 10 M (Degrees)
slp 1 0 Sea Levelp Pressure (hPa)
cape 37 0 CAPE (J/kg)
cin 37 0 CIN (J/kg)
mcape 1 0 MCAPE (J/kg)
mcin 1 0 MCIN (J/kg)
lcl 1 0 LCL (meters AGL)
lfc 1 0 LFC (meters AGL)
 
You're right, that specific humidity is not a variable that is available to output with wrf. It looks like there is one (called QLEV_URB3D) if you happen to be using an urban parameterization scheme. Otherwise, you may have to calculate it during post-processing. I would recommend using either NCL or python to try to get the output you want.
 
If anyone know any scripts or equations for computing Specific humidity at all levels from the given variables in my WRF output, it would be really helpful.
Thank you
 
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