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# g2fshv

Interpolates a vector quantity from a Gaussian grid to a fixed grid.

## Prototype

procedure g2fshv (
ua  : numeric,
va  : numeric,
ub  : float,    ; or double
vb  : float     ; or double
)

## Arguments

ua
va

Vector arrays of 2 or more dimensions whose rightmost two dimensions must be latitude x longitude. The values must be in ascending latitude order.

ub
vb

(output)
Vector arrays of 2 or more dimensions whose rightmost two dimensions must be latitude x longitude. Values will be in ascending latitude order. All but the two rightmost dimensions must be the same as all but the two rightmost dimensions of ua and va.

Since g2fshv is a procedure, the user must explicitly preallocate memory for these return arrays.

## Description

g2fshv interpolates a vector pair on a Gaussian grid (ua,va) to a fixed grid (ub,vb) using spherical harmonics (via the Spherepack code).

Arrays which have dimensions [...] x nlata x nlona should not include the cyclic (wrap-around) points when invoking this procedure. For example, if arrays u and v have dimensions nlata = 64 and nlona = 129, where the "129" represents the cyclic point, then the user should pass the data to g2fshv via:

z = g2fshv(u(...,0:nlona-2), v(...,0:nlona-2),...)  ; does not include cyclic points

This procedure can only be used on grids that span the globe. It cannot be used for limited area grids.

Please read the caveats that you should be aware of when using spherical harmonic regridding.

Use the g2fshv_Wrap procedure if metadata retention is desired. The interface is identical.

## Examples

Example 1

Assume u and v are dimensioned nt x nlat x nlon, and that they are of type float or double.

The code below interpolates from a Gaussian T63 grid (nlat=94, nlon=192) to a fixed 2.5 x 5.0 degree grid (jlat=73,ilon=72):

uNew = new ( (/nt,jlat,ilon/), typeof(u) )
vNew = new ( (/nt,jlat,ilon/), typeof(v) )

g2fshv (u,v, uNew,vNew)

; Use g2fshv_Wrap if metadata retention is desired
; g2fshv_Wrap (u,v, uNew,vNew)

## Errors

ier is equal to:

4 or 10 if nlona (ilon) is less than 4
5 or 10 if nlata (jlat) is less than 3
8 if nlonb is less than 4
9 if nlatb is less than 3