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lapsG

Computes the Laplacian using spherical harmonics, given a scalar z on a gaussian grid.

Prototype

	function lapsG (
		z  : numeric   
	)

	return_val [dimsizes(z)] :  float or double

Arguments

scalar function array (input, two or more dimensions, last two dimensions must be nlat x nlon)

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

Return value

The return type will be double if z is double, and float otherwise. The returned array will be of size dimsizes(z).

Description

Given scalar function z, lapsG computes the Laplacian and returns an array with the same dimensions as z (values will be in ascending latitude order). lapsG operates on a gaussian grid.

This function does not handle missing values. 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 default missing value appropriate to the type of the output.

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).

For example, if an array x has dimensions nlat = 64 and nlon = 129, where the "129" represents the cyclic points, then the user should pass the data to the procedure/function via:

    z = sample ( x([...],:,0:nlon-2) )  ; does not include cyclic points

If the input array z is on a fixed grid, lapsF should be used. Also, note that lapsG is the function version of lapsg.

Examples

Example 1

Read Z (on a gaussian grid) from a netCDF file and compute the Laplacian:

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
begin
   a = addfile("/cgd/cas/shea/MURPHYS/ATMOS/80.nc","r")
   z200 = a->Z(0,{189.},:,:)			; z200 is dimensioned nlat x nlon
   printVarSummary(z200)
   lapl = lapsG(z200)
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)