## hcurl

`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)`

2. 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