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# uv2vrg

Computes the vorticity via spherical harmonics, given the u and v wind components on a gaussian grid.

## Prototype

```	procedure uv2vrg (
u     : numeric,
v     : numeric,
vort  : float or double
)
```

## Arguments

u
v

wind components (input, arrays with two or more dimensions, last two dimensions must be nlat x nlon)

• input values must be in ascending latitude order
• input array must be on a global grid

vort

vorticity (output, same dimensions as u and v, values will be in ascending latitude order)

## Description

Given wind components u and v, uv2vrg computes the vorticity and returns it in the array vort. uv2vrg operates on a gaussian grid.

This procedure does not handle missing values (defined by the _FillValue attribute). If any missing values are encountered in a particular 2D input grid, then all of the values in the corresponding output grid will be set to the missing value defined by the output grid's _FillValue attribute.

Note: For the arrays whose last two dimensions are nlat x nlon, the rest of the dimensions (if any) are collectively referred to as N. If the input/output arrays are just two dimensions, then N can either be considered equal to 1 or nothing at all.

Arrays which have dimensions N x nlat x nlon should not include the cyclic (wraparound) points when invoking the procedures and functions which use spherical harmonics (Spherepack).

If the input arrays u and v are on a fixed grid, uv2vrf should be used. Also, note that uv2vrg is the procedural version of uv2vrG.

Note, if the input arrays are not global or contain missing data, then it is recommended that uv2vr_cfd be used.

## Examples

Example 1

Compute the vorticity given u and v on a gaussian grid. Also, compute the rotational wind components.

```begin
nlat  = 128                                       ; dimensions
mlon  = 256
mlon1 = mlon+1
fbfile = "uv300.hs"

nrec  = fbinnumrec(fbfile)           ; total number of records in the file
ntim  = nrec/2                       ; number of time steps in dataset

uvmsg = 1e+36

vrx   = new ( (/nlat,mlon /), float, uvmsg )  ; vorticity  (same as vort)
ur    = new ( (/nlat,mlon /), float, uvmsg )
vr    = new ( (/nlat,mlon /), float, uvmsg )

do i = 0,nrec-1,2
month = 1                         ; January
if (i .ge. 2) then
month = 7                     ; July
end if

u    = work(:,0:mlon-1)
v    = work(:,0:mlon-1)

uv2vrg   (u,v,vort)               ; u,v ==> vorticity (rel)
vr2uvg   (vort,ur,vr)             ; ur,vr > rotational wind components
end do
end
```

## Errors

If jer or ker is equal to:

1 : error in the specification of nlat
2 : error in the specification of nlon
4 : error in the specification of N (jer only)