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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Jeff,
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<div>Well the expression given second will work with lev set statically before entering the command (doesn't make sense to me to enter it after given the level about which to compute a central difference would have to be known first), but the first expression
(w/ lev first set) gives 'Error from CDIFF: Specified dimension non varying', which is what I thought I would get out of cdiff given lev is set statically. Though the second command may suffice for my purposes. As I said I was able to get it to work, after
having set lev, so I assume the display is appropriate for the lev I choose and no other (I'd imagine it would have to be if the expression is working as it appears, that is the central difference about the set lev, with this approximation valid for the state
of the derivative at the center, ie the level about which the central difference is computed). The syntax is new to me so it is good to learn. Now I just need to get a potential temperature expression to display for me.</div>
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<div>Mason </div>
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<div id="divRpF272790" style="direction: ltr; "><font face="Tahoma" size="2" color="#000000"><b>From:</b> gradsusr-bounces@gradsusr.org [gradsusr-bounces@gradsusr.org] on behalf of Jeff Duda [jeffduda319@gmail.com]<br>
<b>Sent:</b> Tuesday, November 22, 2011 8:41 PM<br>
<b>To:</b> GrADS Users Forum<br>
<b>Subject:</b> Re: [gradsusr] Specialized Display Question<br>
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<div>Mason,<br>
You can use the cdiff command in the z direction to display variables (unfortunately, you can't use it to define variables). However, you can approximate the vertical derivative by copying the method that cdiff uses. If you have geopotential height, then
you have all you need to compute a vertical derivative with respect to height coordinates. You can display the vertical derivative of theta by either of the following:<br>
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'd cdiff(theta,z)'<br>
'd (theta(z+1)-theta(z-1)) / (hgtprs(z+1)-hgtprs(z-1))<br>
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If you want to just view the gradient on one pressure surface, set the level that surface, then enter the command.<br>
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Jeff<br>
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<div class="gmail_quote">On Tue, Nov 22, 2011 at 7:54 PM, Rowell, Mason D. <span dir="ltr">
<<a href="mailto:Mason.D.Rowell-1@ou.edu" target="_blank">Mason.D.Rowell-1@ou.edu</a>></span> wrote:<br>
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All,<br>
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Is it possible to display the vertical derivative of some quantity (like say temp or potential temp) on a pressure surface? I know I have height in my NARR data, but it is specific to a pressure level (i.e. HGTprs). What I would need is the height just above
the current pressure level and below it in order to get cdiff of say theta and z. I'm not sure how to set the dimensions to do this...I would be okay with just getting this quantity for display at some level height, it doesn't have to be on a pressure surface.<br>
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Mason<br>
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-- <br>
Jeff Duda<br>
Grad student - PhD, Meteorology<br>
University of Oklahoma School of Meteorology - Center for Analysis and Prediction of Storms<br>
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