<!--Copyright (C) 1988-2005 by the Institute of Global Environment and Society (IGES). See file COPYRIGHT for more information.--> <h2><b>hcurl</b></h2><p> <code>hcurl(<i>uexpr,vexpr</i>)</code><p> Calculates the vertical component of the curl (ie, vorticity) at each grid point using finite differencing on the grids provided. It is assumed that <code><i>uexpr</i></code> gives the U Wind component, and that <code><i>vexpr</i></code> provides the V Wind component.<p> <h3>Usage Notes</h3><p> <ol> <li>The alghorithm used for the finite difference calculation is described as an Example for the <a href="gradfunccdiff.html"><code>cdiff</code></a> function.<p> <li>The function assumes an X-Y varying dimension environment, and will not operate unless that is the case. The <a href="gradcomddefine.html"><code>define</code></a> command can be used in conjunction with the <code>hcurl</code> function to create 3 or 4 dimensional fields of vorticity, from which vertical cross-sections could be displayed. <p> <li>The boundaries of the grid are set to missing. <p> <li>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. <p> </ol> <h3>Examples </h3><p> <ol> <li>To display the vorticity: <p> <dd><code>d hcurl(u,v) </code><p> <li>If you want to display a vertical cross section of vorticity, you first need to calculate it over a 3-Dimensional region: <p> <dd><code>set lon 0 360 <dd>set lat -90 90 <dd>set lev 1000 100 <dd>define vort = hcurl(u,v) <dd>set lon -90 <dd>display vort </code> </ol>