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wrf_tk

Calculates temperature in [K] from ARW WRF model output.

Prototype

	function wrf_tk (
		P      : numeric,  
		THETA  : numeric   
	)

	return_val [dimsizes(P)] :  float or double

Arguments

Full pressure (perturbation + base state pressure). The rightmost dimensions are bottom_top x south_north x west_east. Units must be [Pa].

THETA

Potential temperature (i.e, perturbation + reference temperature) with the same dimension structure as P. Units must be [K].

Return value

Temperature in [K]. The multi-dimensional array has the same size as P. The type will be double if P or THETA are double, and float otherwise.

Description

This function returns temperature in [K]. The return variable will contain two attributes:

return_val@description = "Temperature"
return_val@units = "K"

As of version 5.1.0, the return variable will contain the same named dimensions (if any) of THETA. Otherwise, the rightmost two dimensions will be named "south_north" and "west_east".

Examples

Note: 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

Example 1

Read and process a 4d array. The arguments are variables from WRF data.

Note that if your netCDF file doesn't have a ".nc" suffix, you must include it in the call to addfile so it knows what kind of file to open. The addfile call below will cause NCL to look for both a file called "wrfout_d01_2000-01-24_12:00:00.nc" and "wrfout_d01_2000-01-24_12:00:00".

  a = addfile("wrfout_d01_2000-01-24_12:00:00.nc","r")

  P  = a->P                     ; perturbation
  Pb = a->PB                    ; base state pressure
  P  = P + Pb                   ; total pressure

  T = a->T                  ; perturbation potential temperature (theta+t0)
  T = T + 300.

  TK = wrf_tk (P, T)

  printVarSummary(TK)

Example 2

A case with multiple data files such as in ensemble forecasting.

  load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"

  fname = "wrfout_d01_2007-05-03_00:00:00"
  flist = systemfunc("ls ENS_*/"+fname)
  print(flist)

The output yields:

  Variable: flist
  Type: string 
  Total Size: 12 bytes 
              3 values
  Number of Dimensions: 1
  Dimensions and sizes:   [3]
  Coordinates:
  (0)     ENS_1/wrfout_d01_2007-05-03_00:00:00
  (1)     ENS_2/wrfout_d01_2007-05-03_00:00:00
  (2)     ENS_3/wrfout_d01_2007-05-03_00:00:00

  f     = addfiles(flist+".nc","r")
  THETA = addfiles_GetVar(f,flist+".nc","T")
  P     = addfiles_GetVar(f,flist+".nc","P")
  PB    = addfiles_GetVar(f,flist+".nc","PB")
  THETA = THETA + 300.
  P     = P + PB

  TK = wrf_tk(P, THETA)
  printVarSummary (TK)

The output yields:

  Variable: TK 
  Type: float 
  Total Size: 3021372 bytes
              755343 values
  Number of Dimensions: 4 
  Dimensions and sizes:   [Time | 3] x [bottom_top | 41] x [south_north | 69] x [west_east | 89] ; in NCL 5.1.0 
  Coordinates: 
  Number Of Attributes: 2
    units :       K
    description : Temperature

Example 3

The function wrf_user_getvar, (available in the $NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl script) can also be used to calculate many diagnostics in one step.

  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
  tk = wrf_user_getvar(a,"tk",time)  ; calculate tk

You can see some other example scripts and their resultant images at: