hcurl(uexpr,vexpr)
 
Calculates the vertical component of the curl (ie, vorticity) at each grid
point using finite differencing on the grids provided. It is assumed that
uexpr gives the U Wind component, and that
vexpr provides the V Wind component.
cdiff
function.
define command can
be used in conjunction with the hcurl function to create 3 or
4 dimensional fields of vorticity, from which
vertical cross-sections could be displayed. 
d hcurl(u,v) 
set lon 0 360 
- set lat -90 90 
- set lev 1000 100 
- define vort = hcurl(u,v) 
- set lon -90 
- display vort