How to derive Specific Humidity from WRF output ?

[Alfred-Jose]

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)

 

[kwerner]

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.

 

[Alfred-Jose]

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

 

[stanleyakor]

If anyone know any scripts or equations from the given variables in my WRF output, it would be really helpful.
Thank you

I found this for relative humidity: relative humidity

 

[William.Hatheway]

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

specific_humidity_from_dewpoint — MetPy 1.6

unidata.github.io

Might help you get started

 

[Alfred-Jose]

Does qvapor, qrain, qcloud account for specific humidity?

 

[Alfred-Jose]

specific_humidity_from_dewpoint — MetPy 1.6

unidata.github.io

Might help you get started

But dont we require dew point temperature at multiple levels ?

Thank you for your input

 

[Ming Chen]

@Alfred-Jose
If you are familiar with python, you can use the function "specific_humidity_from_mixing_ratio" to obtain SPFH. Please see details here.
Note that QVAPOR is the required and it is a variable included in wrfout.

 

[Alfred-Jose]

Thank you so much, @Ming Chen, I was having doubts earlier, now I am looking into my plots and am able to see near observation values, while using the QVAPOR variable.

Thank you all