Extracts data from ARW WRF model output, and does basic diagnostics calculations.
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl" ; These two libraries are automatically load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl" ; loaded from NCL V6.4.0 onward. ; No need for user to explicitly load. function wrf_user_getvar ( file_handle : file or list, variable : string, time : integer ) return_val : numeric
Variable to retrieve. This can be either a variable in the ARW WRF output file(s), or a diagnostic - a limited number of diagnostics are available, see description below.time
Time in file to retrieve. A value of -1 will retrieve all times in the file(s).
Data of requested field.
This function extracts data from the ARW WRF file, and, if available, calculates the requested diagnostic.
For WRF variable names and their definitions, you can easily check them by using "ncl_filedump":
Available diagnostics (some diagnostics - marked in red below - are only available in version 6.6.0 or later):
|avo||absolute vorticity [10-5 s-1]|
|eth||Equivalent Potential Temperature [K]|
|cape_2d||Returns 2D fields mcape/mcin/lcl/lfc|
Bug fixed in NCL V6.4.0: the surface pressure values were not being converted to hPa properly as required by the internal cape routines.
|cape_3d||Returns 3D fields cape and cin|
This diagnostic is a special one that allows variable to either just be "cfrac", in which a series of default values are assumed, or it can be an array of six ordered string values that represent the following:
|ctt||Cloud Top Temperature [degC]|
Bug fixed in NCL V6.4.0: the pressure values were not being converted properly. Also, the values are now returned in degC and not in degK as previously advertised.
|mdbz||Maximum reflectivity [dBZ]|
|geopt/geopotential||Full model geopotential [m2 s-2]|
|helicity||Storm Relative Helicity [m-2/s-2]|
Note: this is over the 0-3000 m AGL layer.
Bug fixed in NCL V6.4.0: the calculation was incorrectly using the temperature values for the water vapor mixing ratio, making the output results nonsensical.
|p/pres||Full model pressure [Pa]|
|pressure||Full model pressure [hPa]|
|pvo||potential vorticity [PVU]|
|pw||Precipitable Water |
Bug fixed in NCL V6.4.0: the returned array will now have named dimensions.
|rh2||2m Relative Humidity [%]|
|rh||Relative Humidity [%]|
|slp||Sea level pressure [hPa]|
|ter||Model terrain height [m]|
|td2||2m dew point temperature [C]|
|td||Dew point temperature [C]|
|th/theta||Potential temperature [K]|
|times||Times in file (return strings - recommended)|
|Times||Times in file (return characters)|
|tv||Virtual temperature [K]|
|twb||Wet bulb temperature [K]|
|updraft_helicity||Updraft helicity [m-2/s-2]|
|ua||U component of wind on mass points|
|va||V component of wind on mass points|
|wa||W component of wind on mass points|
|wspd_wdir||grid relative wind speed and direction|
|wspd_wdir10||10m grid relative wind speed and direction|
|uvmet_wspd_wdir||earth relative wind speed and direction|
|uvmet10_wspd_wdir||10m earth relative wind speed and direction|
|uvmet10||10m U and V components of wind rotated to earth coordinates|
|uvmet||U and V components of wind rotated to earth coordinates|
|z/height||Full model height [m]|
wrf_user_getvar is modifiable by the user, if you want to add your own diagnostics. To add your own diagnostics:
- Copy the file "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"
to your own directory.
- Edit this file with any UNIX editor and look for the lines:
undef("wrf_user_getvar") function wrf_user_getvar( file_handle, varin[*]:string, time:integer )Before the final lines in this function:
return(var) endAdd these lines, replacing newvar as appropriate:
if( variable .eq. "newvar" ) then . . . fill in code here . . . end if
- To use the new version of this function, you can do one of two things:
- Copy your modified script over
use the new "wrf_user_getvar" with your new entry:
xxx = wrf_usr_getvar(f,"XXX",0)
- Remove all but the modified "wrf_user_getvar" function from your
copy, rename the function ("wrf_user_getvar2"), and rename the file
("my_new_script.ncl"). You will need to load your new script to use the
load "my_new_script.ncl" xxx = wrf_usr_getvar2(f,"XXX",0)
- Copy your modified script over "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl" and use the new "wrf_user_getvar" with your new entry:
wrf_user_getvar is part of a library of functions and procedures in WRFUserARW.ncl written to help users plot ARW WRF model data.
See the full list of WRF functions.
Get variables from a single WRF ARW file:
a = addfile("wrfout_d01_2000-01-24_12:00:00.nc","r") time = 1 slp = wrf_user_getvar(a,"slp",time) ; slp tc2 = wrf_user_getvar(a,"T2",time) ; T2 in Kelvin u10 = wrf_user_getvar(a,"U10",time) ; u at 10 m v10 = wrf_user_getvar(a,"V10",time) ; v at 10 m ua = wrf_user_getvar(a,"ua",time) ; u on mass points va = wrf_user_getvar(a,"va",time) ; v on mass points avo = wrf_user_getvar(a,"avo",-1) ; calculate avo for all times in file
As of NCL V6.0.0, you can get a variable from a list of WRF ARW NetCDF files:
files = systemfunc("ls -1 wrfout_d01_2000*") + ".nc" a = addfiles(files,"r") slp = wrf_user_getvar(a,"slp",-1)