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vr2uvG

Computes the rotational wind components via spherical harmonics, given an array containing relative vorticity on a gaussian grid.

Prototype

	function vr2uvG (
		vr  : numeric   
	)

	return_val [2,dimsizes(vr)] :  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
• array must be on a global grid

Return value

The returned array will be dimensioned 2 x dimsizes(vr), where the 0-th element of the leftmost dimension contains the u component and the 1-th element of the leftmost dimension contains the v component (both in ascending latitude order). The returned array will be of type double if the input is double, and float otherwise.

Description

vr2uvG computes the rotational wind components given an array, vr, containing relative vorticity. vr2uvG operates on a gaussian grid.

This function 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 function, or any procedure or function which uses spherical harmonics (Spherepack).

If the input array vr is on a fixed grid, vr2uvF should be used. Also, note that vr2uvG is the function version of vr2uvg.

Use the vr2uvG_Wrap function if metadata retention is desired. The interface is identical.

See Also

vr2uvG_Wrap, vr2uvF, vr2uvg, vr2uvf, vrdv2uvG, vrdv2uvf, vrdv2uvF, vrdv2uvf, uv2vrdvG, uv2vrdvF, uv2vrG, uv2vrF, uv2vr_cfd

Examples

Example 1

Let vrt(nlat,mlon) be on a gaussian grid, and contain the relative vorticity. Then:

uvr = vr2uvG (vrt)

; Use vr2uvG_Wrap if metadata retention is desired
; uvr = vr2uvG_Wrap (vrt)

will return the rotational zonal and meridional wind components.

uvr(0,nlat,mlon) <== ROTATIONAL zonal wind components
uvr(1,nlat,mlon) <== ROTATIONAL meridional wind components

These values are the same as those returned by the procedural version of this routine but the user does not have to explicitly allocate memory. For example:

  ur = new (dimsizes(vrt), typeof(vrt))
  vr = new (dimsizes(vrt), typeof(vrt))
  vr2uvg (vrt, ur, vr)   

Example 2

Let vrt(ntim,klev,nlat,mlon) be on a gaussian grid, and contain the relative vorticity. Then:

  uvr = vr2uvG (vrt)

  ; Use vr2uvG_Wrap if metadata retention is desired
  ; uvr = vr2uvG_Wrap (vrt)

will return the rotational zonal and meridional wind components.

uvr(0,ntim,klev,nlat,mlon) <== ROTATIONAL zonal wind components
uvr(1,ntim,klev,nlat,mlon) <== ROTATIONAL meridional wind components

Example 3

Read u/v (on a gaussian grid) from a netCDF file, compute relative vorticity, and then compute the rotational wind components.

  f = addfile ("UV.nc", "r")
  u = f->U
  v = f->V

  vrt = uv2vrG (u, v)   ; compute vorticity
  uvr = vr2uvG (vrt)    ; compute rotational wind components

  ; Use vr2uvG_Wrap if metadata retention is desired
  ; uvr = vr2uvG_Wrap (vrt)   ; compute rotational wind components

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)

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