
wrf_slp
Calculates sea level pressure from ARW WRF model output.
Prototype
function wrf_slp ( Z : numeric, T : numeric, P : numeric, Q : numeric ) return_val [dimsizes(Z)] : float or double
Arguments
ZGeopotential height in [m] with at least 3 dimensions. It must be on the ARW WRF unstaggered grid. The rightmost three dimensions must be level bottom_top x lat (south_north) x lon (west_east).
TTemperature in [K]. An array with the same dimensionality as Z. This variable can be calculated by wrf_tk.
PFull pressure (perturbation + base state pressure) in [Pa]. An array of the same dimensionality as Z.
QWater vapor mixing ratio in [kg/kg]. An array of the same dimensionality as Z.
Return value
This function returns an array whose rightmost two dimensions are the same as the rightmost two dimensions of the input variables (lat x lon). The type will be double if any of the input is double, and float otherwise.
Description
This function calculates sea level pressure from ARW WRF model output. It also makes sure there are no negative values in Q by setting them all to 0.
The return variable will contain two attributes:
return_val@description = "Sea Level Pressure"
return_val@units = "hPa"
As of version 5.1.0, the return variable will contain all but the rightmost third named dimensions (if any) of T. Otherwise, the rightmost two dimensions will be named "south_north" and "west_east".
See Also
See the full list of WRF functions.
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
T = nc_file->T(time,:,:,:) th = T + 300. P = nc_file->P(time,:,:,:) PB = nc_file->PB(time,:,:,:) p = ( P + PB ) tk = wrf_tk( p , th ) QVAPOR = nc_file->QVAPOR(time,:,:,:) PH = nc_file->PH(time,:,:,:) PHB = nc_file->PHB(time,:,:,:) var = ( PH + PHB ) / 9.81 dim = dimsizes(var) z = 0.5 * ( var(0:dim(0)-2,:,:) + var(1:dim(0)-1,:,:) ) slp = wrf_slp( z, tk, p, QVAPOR )Example 2
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 slp = wrf_user_getvar(a,"slp",time) ; calculate SLPYou can see some other example scripts and their resultant images at:
http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/