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wrf_user_getvar

Extracts data from ARW WRF model output, and does basic diagnostics calculations.

Available in version 4.3.1 or later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"

	function wrf_user_getvar (
		nc_file   : file,     
		variable  : string,   
		time      : integer   
	)

	return_val  :  numeric

Arguments

nc_file

Reference to an input netCDF file opened with addfile.

variable

Variable to retrieve. This can be either a variable in the ARW WRF output file, or a diagnostics - a limited number of diagnostics are available, see description below.

time

Time in file to retrieve. As of version 5.1.0, "-1" will retrieve all times in the file.

Return value

Data of requested field.

Description

This function extracts data from the ARW WRF file, and, if available, calculates requested diagnostic.

For WRF variable names and their definitions, you can easily check them by using "ncl_filedump":

  ncl_filedump wrfout_d01_2000-01-24_12:00:00.nc

Available diagnostics (some diagnostics - marked in red below - are only available since version 5.1.0):

avo: absolute vorticity [10-5 s-1]
cape_2d: Returns 2D fields mcape/mcin/lcl/lfc
cape_3d: Returns 3D fields cape and cin
dbz: Reflectivity [dBZ]
mdbz: Maximum reflectivity [dBZ]
geopt/geopotential: Full model geopotential [m2 s-2]
lat: latitude
lon: longitude
p/pres: Full model pressure [Pa]
pressure: Full model pressure [hPa]
pvo: potential vorticity [PVU]
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]
tc: Temperature [C]
th/theta: Potential temperature [K]
tk: Temperature [K]
ua: U component of wind on mass points
va: V component of wind on mass points
wa: W component of wind on mass points
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( nc_file:file, varin[*]:string, time:integer )

Before the final lines in this function:

  return(var)

end

Add 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:
1. Copy your modified script over "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl" and use the new "wrf_user_getvar" with your new entry:
```
load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"
xxx = wrf_usr_getvar(f,"XXX",0)
```
2. 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 the above script and your new script to use the new function:
```
load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"
load "my_new_script.ncl"
xxx = wrf_usr_getvar2(f,"XXX",0)
```

wrf_user_getvar is part of a library of functions and procedures in WRFUserARW.ncl written to help users plot ARW WRF model data.

WRF-related questions should be sent to wrfhelp@ucar.edu.

Examples

Example 1

  load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
  load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"

  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