free grads

(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.

Usage Notes

1. The alghorithm used for the finite difference calculation is described as an Example for the cdiff function.

   
   

2. The function assumes an X-Y varying dimension environment, and will not operate unless that is the case. The 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.

   
   

3. The boundaries of the grid are set to missing.

   
   

4. The radius of the earth used in the calculation is in meters; thus the units of the wind expressions provided would normally be m/s.

   
   

Examples

1. To display the vorticity:

   
   

   d hcurl(u,v)

   
   

   If you want to display a vertical cross section of vorticity, you first need to calculate it over a 3-Dimensional region:

   
   

   set lon 0 360

   set lat -90 90

   set lev 1000 100

   define vort = hcurl(u,v)

   set lon -90

   display vort