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wrf_uvmet

Rotates u,v components of the wind to earth coordinates.

Prototype

	function wrf_uvmet (
		u           : numeric,  
		v           : numeric,  
		lat         : numeric,  
		lon         : numeric,  
		cen_lon [1] : numeric,  
		cone    [1] : numeric   
	)

	return_val  :  float or double

Arguments

u
v

U,V components of the wind. As of V5.1.0, these can be unstaggered or staggered, and must be at least two-dimensional.

If they are unstaggered, then the rightmost two dimensions must be south_north x west_east.

If they are staggered, then the rightmost two dimensions must be south_north x west_east_stag for u and south_north_stag x west_east for v.

lat
lon

Latitude and longitude arrays. These arrays can either be:

two-dimensional of size south_north x west_east
multi-dimensional with the same number of dimensions as u and v, but with rightmost dimensions south_north x west_east and the same leftmost dimensions as u and v
multi-dimensional with one fewer dimensions as u and v, with rightmost dimensions south_north x west_east and the same leftmost dimensions as u and v, minus the third-from-the-right dimension of u and v

So, for example, if u,v are on unstaggered grids and dimensioned Time x bottom_top x south_north x west_east, then lat, lon can be:

south_north x west_east
Time x south_north x west_east

cen_lon

A scalar value. This is the standard longitude around which the domain is projected.

cone

A scalar value. The cone factor used in the model domain projection.

Return value

The return array will be U and V components of the wind rotated to earth coordinates. It will be a multi-dimensional array whose leftmost dimension is 2, whose rightmost two dimensions are south_north x west_east, and whose dimensions inbetween are the leftmost dimensions of u and v.

So, for example, if u, v are on unstaggered grids and dimensioned:

Time x bottom_top x south_north x west_east

then the return value (uvmet) will be dimensioned:

2 x Time x bottom_top x south_north x west_east

where

umet = uvmet(0,:,:,:,:)
vmet = uvmet(1,:,:,:,:)

Description

The return variable will contain the U and V components of the wind after they have been rotated to earth coordinates, and two attributes:

return_val@description = "u,v met velocity"
return_val@units = "m/s"

The return variable will also contain named dimensions if u and/or v contain named dimensions.

As of V5.1.0, the input U,V arrays can be staggered or unstaggered.

As of V5.2.1, missing values are ignored.

Rotated winds are needed when comparing model data with observations.

Examples

Example 1

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

If you ask for the "uvmet" diagnostic, then internally the wrf_user_unstagger function is called to do the unstaggering, if necessary, and then the wrf_uvmet function is called to do the rotation.

  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
  uvm = wrf_user_getvar(a,"uvmet",time)         
        ; umet and vmet averaged to mass points
        ; This is a 4D array where
        ; uvm(0,:,:,:) is umet, and
        ; uvm(1,:,:,:) is vmet, and
        ; This function rotate winds to earth coord.

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