z2geouv

Computes the geostrophic zonal and meridional wind components using geopotential height.

Prototype

	function z2geouv (
		z       : numeric,  
		lat [*] : numeric,  
		lon [*] : numeric,  
		iopt    : integer   
	)

Arguments

A multi-dimensional array containing the geopotential heights. The two rightmost dimensions must be lat and lon.

A one-dimensional array containing the latitude coordinates in degrees. Must be a monotonically increasing or decreasing array.

A one-dimensional array containing the longitude coordinates in degrees. Must be in ascending order and is assumed to be equally spaced.

A scalar integer: iopt=0 -> z is not cyclic in longitude; iopt=1 -> z is cyclic in longitude.

Return value

A double array is returned if z is double; a float array is returned otherwise.

If the rightmost dimensions of z are nlat x mlon and N represents all other variable dimensions, then the u and v wind components are returned as a variable dimensioned 2 x N x nlat x mlon. The leftmost dimension of size 2 contains the u [zonal] and v [meridional] wind components.

The examples clarify the above information.

Description

Available in version 4.2.0.a33 or later.

This function computes geostrophic wind components on a latitude-longitude grid using finite differences. If a latitude is exactly at the equator, the function sets the components to missing. The grid need not be global and missing values are allowed.

Examples

Example 1

Assume z is a global grid with dimension sizes (ntim,klev,nlat,mlon). There are no missing values and the data are periodic in longitude. Then:

   uv = z2geouv (z,lat,lon, 1)  ; uv(2,ntim,klev,nlat,mlon)  

Assume z is an array on a limited area of the globe with dimension sizes (ntim=100,nlat=34,mlon=60).

  uv = z2geouv (z,lat,lon, 0)  ==> uv(2,100,34,60)   

Using the results of Example 1, create separate u and v arrays with attributes and coordinate arrays. Note: This is not necessary. It is presented for illustration only.

  u  = uv(0,:,:,:,:)                                ; u(ntim,klev,nlat,mlon)
  u@long_name = "geostrophic zonal wind component"
  u@units     = "m/s"

  u!0    = "time"
  u!1    = "lev"
  u!2    = "lat"
  u!3    = "lon"

  u&time =  time
  u&lev  =  lev
  u&lat  =  lat
  u&lon  =  lon

  [same for v]