<div dir="ltr"><div><div>Gradients: zonal [ d()/dx ] and meridional [ d()/dy ]<br><br></div><div>[1] <br>WRF data are on a <span style="color:rgb(0,0,255)"><b>regional </b></span> <b>curvilinear</b> grid. <br><br>[2]<br>NCL's <span style="color:rgb(255,0,0)"><b>gradient calculation functions</b></span> require data to be on a <b>rectilinear</b> grid.<br><br></div>[3] <br> Different functions should be used for global and regional rectilinear grids.<br><br>For global grids, NCL's gradient calculation functions use <i>highly accurate</i> spherical harmonics to calculate gradients<br>For regional grids, NCL's gradient calculation functions use centered finite differences <br><br></div><div>[4]<br>NCL has no single function to directly calculate the zonal and meridional gradients on a curvilinear grid. <br><br>[5]<br></div><div>You must (a) interpolate the WRF data to a rectilinear grid of about the same resolution or, ?better? slightly higher resolution; (b) calculate the gradients on the rectilinear grid using <b><a href="http://www.ncl.ucar.edu/Document/Functions/Contributed/grad_latlon_cfd.shtml">grad_latlon_cfd</a></b>; (c) reinterpolate from the rectilinear grid back onto the original WRF grid.<br><br></div><div>[6] See:<br><a href="http://www.ncl.ucar.edu/Applications/ESMF.shtml">http://www.ncl.ucar.edu/Applications/ESMF.shtml</a><br></div><div>Examples 29 and 37<br></div><div>Here, the divergence was calculated [ <b><a href="http://www.ncl.ucar.edu/Document/Functions/Built-in/uv2dv_cfd.shtml"><strong>uv2dv_cfd ] </strong></a></b><strong></strong>but you can use the<b><strong> grad_latlon_cfd </strong></b><strong></strong>function<b><strong>.<br></strong></b></div><div>===================================================================<br><br><a href="http://www.ncl.ucar.edu/Applications/gradients.shtml">http://www.ncl.ucar.edu/Applications/gradients.shtml</a><br><a href="http://www.ncl.ucar.edu/Document/Functions/Contributed/grad_latlon_cfd.shtml">http://www.ncl.ucar.edu/Document/Functions/Contributed/grad_latlon_cfd.shtml</a><br><br><br></div><div>FYI only: global <br><a href="http://www.ncl.ucar.edu/Document/Functions/Built-in/gradsg.shtml">http://www.ncl.ucar.edu/Document/Functions/Built-in/gradsg.shtml</a><br><a href="http://www.ncl.ucar.edu/Document/Functions/Built-in/gradsf.shtml">http://www.ncl.ucar.edu/Document/Functions/Built-in/gradsf.shtml</a><br><br></div><div>HTH<br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Aug 16, 2018 at 6:28 AM, Ty Buckingham <span dir="ltr"><<a href="mailto:ty.buckingham@manchester.ac.uk" target="_blank">ty.buckingham@manchester.ac.uk</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">




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<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">Hi all,
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<div>I'm probably overthinking this, but I'm struggling isolating the d/dx and d/dy of a variable (in my case, absolute vorticity from WRF output).</div>
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<div>Is there an easy way to compute this?</div>
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<div>Thanks</div><span class="HOEnZb"><font color="#888888">
<div>Ty</div>
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