NCL Home > Documentation > Functions > Spherical harmonic routines


Computes the vector Laplacian using spherical harmonics, given a vector quantity (u,v) on a fixed grid.


	procedure lapvf (
		u     : numeric,          
		v     : numeric,          
		ulap  : float or double,  
		vlap  : float or double   



vector field arrays (input, two or more dimensions, last two dimensions must be nlat x nlon)

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


vector Laplacian arrays (output, same dimensions as u, v, values will be in ascending latitude order)


Given vector field u and v, lapvf computes the Laplacian vector and returns the results in the arrays ulap and vlap. lapvf operates on a fixed grid. If the input arrays u and v are on a gaussian grid, lapvg should be used.

This procedure 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 grids will be set to the missing value defined by the output grids' _FillValue attributes.

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

See Also

lapvg, lapsF, lapsG, ilapvf, ilapvg, ilapsf


Example 1

Read u and v (on a fixed grid) from a netCDF file and compute the vector Laplacian:

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
   a = addfile("/cgd/cas/shea/MURPHYS/ATMOS/","r")
   v200 = a->V(0,{189.},:,:)			; v200 is dimensioned nlat x nlon
   u200 = a->U(0,{189.},:,:)			; u200 is dimensioned nlat x nlon
   lapl_v = v200				; preallocate space for the returned array
   lapl_u = u200				; preallocate space for the returned array


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)