Re: vcMapDirection resource

From: Mary Haley <haley_at_nyahnyahspammersnyahnyah>
Date: Thu Aug 04 2011 - 08:28:48 MDT

Hi TJ,

I admit I've never understood this resource very well. Dave Brown is out of the office, but here's an explanation from him (modified slightly to make sense in this context) that he sent to another user:

By default, the vector direction is mapped into the coordinate space defined by the coordinate variables. This is appropriate for horizontal vectors drawn on a map, but not for vectors in a vertical space where the Y axis and the X Axis have completely unrelated units. To fix this you should set the resource vcMapDirection to False. However, it also has the effect of always making the positive Y direction from bottom to top. If the vertical component is positive from top to bottom of the atmosphere, then you will need to multiply the vertical component by -1.0 to get the result you are looking for.


On Aug 3, 2011, at 11:54 PM, wxtofly wrote:

> I am confused by this resource as the examples are not consistent with its use and I don't really understand what it does in the absence of an underlying map as on the attached windgram plots.
> I have attached two of my windgrams, one produced without any mention of vcMapDirection which therefore would use the true default, and the other with
> uv_res@vcMapDirection=false. As you can see they are nearly but not exactly identical. (gwenview or something similar next prev to rock between them)
> On the NCAR site, the 1 special example meteo.ncl uses uv_res@vcMapDirection=false. The 5 wrf_meteo(1-5).ncl omit the resource. Which is "correct."
> What would I expect the effects to be?
> Thanks for you help.
> TJ Olney
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Received on Thu Aug 4 08:28:54 2011

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