Calculates potential vorticity from WRF model output.
function wrf_pvo ( u : numeric, v : numeric, THETA : numeric, P : numeric, msfu : numeric, msfv : numeric, msfm : numeric, cor : numeric, dx  : numeric, dy  : numeric, opt  : integer ) return_val [dimsizes(THETA)] : float or double
X-wind component. An array whose rightmost three dimensions are bottom_top x south_north x west_east_stag.v
Y-wind component. An array whose rightmost three dimensions are bottom_top x south_north_stag x west_east, and whose leftmost dimensions are the same as u's.THETA
Potential temperature in K. An array whose rightmost dimensions are bottom_top x south_north x west_east, and whose leftmost dimensions are the same as u's.P
Full pressure (perturbation + base state pressure). An array with the same dimensionality as THETA. Units must be [Pa].msfu
Map scale factor on u-grid. An array whose rightmost two dimensions are the same as u's. If it contains additional leftmost dimensions, they must be the same as the u and v arrays.msfv
Map scale factor on v-grid. An array with the same number of dimensions as msfu, whose rightmost two dimensions are the same as v's. If it contains additional leftmost dimensions, they must be the same as the u and v arrays.msfm
Map scale factor on mass grid. An array with the same number of dimensions as msfu and msfv, whose rightmost two dimensions are south_north x west_east. If it contains additional leftmost dimensions, they must be the same as the u and v arrays.cor
Coriolis sine latitude term. An array of the same dimensionality as msfm.dx
A scalar representing the grid spacing in X.dy
A scalar representing the grid spacing in Y.opt
An integer option, not in use yet. Set to 0.
Potential vorticity at each grid point. The multi-dimensional array will contain the same size and named dimensions as THETA. If THETA does not contain any named dimensions, the rightmost two dimensions will be named "south_north" and "west_east". The type will be double if any of the input is double, and float otherwise.
This function returns potential vorticity in "Potential Vorticity Unit (PVU)". 1 PVU = 1.0 x 10^(-6) m^2 s^(-1) K kg^(-1).
The return variable will contain two attributes:
return_val@description = "Potential Vorticity"
return_val@units = "PVU"
Questions on this function should be sent to email@example.com.
See the full list of WRF functions.
Note: for WRF variable names and their definitions, you can easily check them by using "ncl_filedump":
nc_file = addfile("wrfout_d01_2000-01-24_12:00:00.nc","r") U = nc_file->U V = nc_file->V THETA= nc_file->T P = nc_file->P PB = nc_file->PB MSFU = nc_file->MAPFAC_U MSFV = nc_file->MAPFAC_V MSFM = nc_file->MAPFAC_M COR = nc_file->F DX = nc_file@DX DY = nc_file@DY THETA = THETA + 300. ; potential temperature in K. P = P + PB ; full pressure in Pa. pvo = wrf_pvo( U, V, THETA, P, MSFU, MSFV, MSFM, COR, DX, DY, 0)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") pvo = wrf_user_getvar(a,"pvo",-1) ; calculate pvo for all times in fileYou can see some other example scripts and their resultant images at: