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# vrdv2uvg

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

## Prototype

```	procedure vrdv2uvg (
vr  : numeric,
dv  : numeric,
u   : float,    ; or double
v   : float     ; or double
)
```

## Arguments

vr

vorticity array (input, array 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

dv

divergence array (input, same dimensions as vr)

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

u
v

wind components (output, same dimensions as vr and dv, values will be in ascending latitude order)

## Description

vrdv2uvg computes the wind components given vorticity and divergent arrays vr and dv and stores the results in the arrays u and v. vrdv2uvg 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 grids will be set to the missing value defined by the output grids' _FillValue attributes.

Input arrays should not include the cyclic (wraparound) points when invoking this procedure, or any procedure or function which uses spherical harmonics (Spherepack).

If the input arrays vr and dv are on a fixed grid, vrdv2uvf should be used. Also, note that vrdv2uvg is the procedural version of vrdv2uvG.

## Examples

Example 1

Given the wind components u and v (on a gaussian grid), compute the relative vorticity and divergence, and then reconstruct the wind components from the vorticity and divergence fields.

```begin
nlat  = 128                                       ; dimensions
mlon  = 256
mlon1 = mlon+1
fbfile = "uv300.hs"
; Generic Workstation setup
nrec  = fbinnumrec(fbfile)           ; total number of records in the file
ntim  = nrec/2                       ; number of time steps in dataset

uvmsg = 1e+36

dv    = new ( (/nlat,mlon /), float, uvmsg )  ; divergence
vort  = new ( (/nlat,mlon /), float, uvmsg )  ; vorticity  (relative)
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

work = fbinrecread(fbfile,i  ,(/nlat,mlon1/),"float")
u    = work(:,0:mlon-1)
v    = work(:,0:mlon-1)

uv2vrdvg (u,v, vort,dv)           ; u,v ==> div and vort
vrdv2uvg (vort,dv, uu,vv)         ; vr,dv > reconstruct original wind
end do
end
```
Example 2

Read ECMWF complex coefficients associated with vorticity and divergence. Compute the wind components.

Note: the procedure vrdv2uvg can handle all times, levels with one call. However, it will use lots of temporary memory. This example illustrates processing one time and level at a time. It is a bit less efficient but it reduces memory considerably.

```
;***************************************************
; read DIV and VORT; complex
; ( initial_time0, lv_HYBL4,real_imaginary, g50_lat_2, g50_lon_3)
; calculate wind components
;***************************************************
U  = new ( (/ntim,klev,nlat,mlon/), "float", "No_FillValue")
V  = new ( (/ntim,klev,nlat,mlon/), "float", "No_FillValue")

do nt=0,ntim-1
do kl=0,klev-1
ab     = f->D_GDS50_HYBL(nt,kl,:,:,:)
DIV    = shsgC(ab, mlon)
ab     = f->VO_GDS50_HYBL(nt,kl,:,:,:)
VORT   = shsgC(ab, mlon)

vrdv2uvg(VORT,DIV,U(nt,kl,:,:),V(nt,kl,:,:))
end do
end do

```

## 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)