# 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:

then the return value (Timexbottom_topxsouth_northxwest_east

*uvmet)*will be dimensioned:

2 xTimexbottom_topxsouth_northxwest_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.

## See Also

See the full list of WRF functions.

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

http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/