# vhagC

Computes vector spherical harmonic analysis of vector fields on a gaussian grid via spherical harmonics.

## Prototype

function vhagC ( u : numeric, v : numeric ) return_val : float or double

## Arguments

*u*

*v*

vector function to be analyzed (input, array with two or more
dimensions). The two rightmost dimensions must be *nlat* x
*nlon*.

- input values must be in ascending latitude order
- input arrays must be on a global grid

## Return value

*bc* will contain the vector spherical harmonic coefficients. The user need not
preallocate this array since the function will do so.

If the rightmost two dimensions of *u* and *v* are *nlat* x
*nlon* then the second-to-the-rightmost dimension of *bc* is
*nlat* and the rightmost dimension (*N*) is a function of
the comparative size of *nlat* and *nlon*. It may be
determined as follows:

N = minimum[nlat, (nlon )/2] if nlon is evenAn additional dimension of length 4 is added to address the real and imaginary parts associated with the u and v components.

N = minimum[nlat, (nlon+1)/2] if nlon is odd

If *u* and *v* are two-dimensional arrays (nlat,nlon), then
*bc*(0,nlat,N) will contain the "real" coefficients [u].

bc(1,nlat,N) would contain the "imaginary" coefficients [u]If

bc(2,nlat,N) would contain the "real" coefficients [v]

bc(3,nlat,N) would contain the "imaginary" coefficients [v]

*u*and

*v*are three-dimensional arrays (nt,nlat,nlon), then:

bc(0,nt,nlat,N) would contain the "real" coefficients [u]If

bc(1,nt,nlat,N) would contain the "imaginary" coefficients [u]

bc(2,nt,nlat,N) would contain the "real" coefficients [v]

bc(3,nt,nlat,N) would contain the "imaginary" coefficients [v]

*u*and

*v*are four-dimensional arrays (nt,nlvl,nlat,nlon), then:

bc(0,nt,nlvl,nlat,N) will contain the "real" coefficients [u]etc.

bc(1,nt,nlvl,nlat,N) will contain the "imaginary" coefficients [u]

bc(2,nt,nlvl,nlat,N) will contain the "real" coefficients [v]

bc(3,nt,nlvl,nlat,N) will contain the "imaginary" coefficients [v]

The return array will be double if the input is double, and float otherwise.

**Note:** The coefficients contained in *bc* are in mathematical
coordinates. Please read the documentation at:

http://www.scd.ucar.edu/css/software/spherepack/vhagc.txtThis is tricky and care must be taken to handle the coefficients correctly.

## Description

**vhagC** performs the vector spherical harmonic
analysis on the arrays *u* and *v*. In general,
**vhagC** (performs vector spherical harmonic analysis)
is used in conjunction with **vhsgC** (performs vector
spherical harmonic synthesis). Note that both
**vhagC** and **vhsgC** operate on a
gaussian grid.

NOTE: This function does not allow for missing data (defined by the _FillValue attribute)
to be present. The input arrays should **not** include the cyclic (wraparound) points, as
this function uses spherical harmonics. (NCL procedures/functions that
use spherical harmonics should never be passed input arrays that include cyclic points.)

If the input arrays *u* and *v* are on a fixed
grid, **vhaeC** should be used. Also, note
that **vhagC** is the function version of
**vhagc**.

## See Also

**vhagc**, **vhsgC**, **vhsgc**, **vhaeC**,
**vhaec**, **vhsec**, **vhseC**

## Examples

In the examples below, u and v are on a gaussian grid.

**Example 1**

u(nlat,nlon), v(nlat,nlon)

bc =vhagC(u,v) [do something with the coefficients] UV =vhsgC(bc,nlon) ; orvhsgc(bc(0,:,:),bc(1,:,:),bc(2,:,:),bc(3,:,:),u,v)

**Example 2**

u(nt,nlat,nlon), v(nt,nlat,nlon)

bc =vhagC(u,v) [do something with the coefficients] UV =vhsgC(bc,nlon) ; orvhsgc(bc(0,:,:,:),bc(1,:,:,:),bc(2,:,:,:),bc(3,:,:,:),u,v)

**Example 3**

u(nt,nlvl,nlat,nlon), v(nt,nlvl,nlat,nlon)

bc =vhagC(u,v) [do something with the coefficients] UV =vhsgC(bc,nlon) ; orvhsgc(bc(0,:,:,:,:),bc(1,:,:,:,:),bc(2,:,:,:,:),bc(3,:,:,:,:),u,v)