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[IDV #WYC-198714]: IDV 4.1u1: Vertical cross section plots conforming to variable surface elevation

> 
> On Dec 18, 2013, at 1:36 PM, Unidata IDV Support <address@hidden> wrote:
> 
> > Dave,
> >     According to Tom Rink:
> > "Sigma coordinates are often terrain following so there would be missing
> > data near (depending on resolution) and below the terrain.  When transformed
> > to physical space, grid surfaces can have irregularities (concave 
> > structures) which
> > can be difficult for the resample algorithm. "
> >
> > So, I would say the solution is to transfer the data to the grid format 
> > using the WRF post process script before the visualization.
> >
> 
> 
> Yuan,
> 
> Hmmm. I'm not sure what "the grid format" means, nor do I know what "the WRF 
> post process script" is. Guess I'll have to poke around on the WRF Web site 
> to see what I can find.
> 
> If I had to guess, I'd guess that "the grid format" means data are 
> interpolated and extrapolated to constant pressure surfaces, so that when 
> pressure is the vertical coordinate, the grid points form a nice rectangular 
> array and can be contoured without complications by typical contouring 
> routines. The "WRF post process script" would presumably do does this 
> interpolation and extrapolation to constant pressure surfaces.
> 
> The problem with this is that some pressure surfaces will lie below the 
> terrain, and the plot will show those values (rather than ending at the 
> terrain surface or half a grid level above it). This would certainly be 
> misleading.
> 
> Maybe it's just hard to create a plot that follows the terrain at the bottom 
> boundary. I could have sworn, though, that NCAR graphics does this.
> 
> -- Dave

Dave,
      We normally recommend the IDV user to run the post process script first 
to convert to pressure coordinate.  It is very expensive in CPU and memory to 
do the unstaggering in the IDV. The dataset from your WRF is pretty small, and 
this is why you don't feel the slowness in the IDV when creating this display. 
As I know the post process script can generate grib1/grib2 format and Grads 
format output, maybe gempack format too. I believe that the WRF output need to 
be post processed before loading to the NCL.


Yuan
> 
> ***************************************************************
> *   Dr. Dave Dempsey                             |       ^   ___       \|/    
>  *
> *   Dept. of Earth & Climate Sciences   |  ) ^     /||_||\    --0--  *
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> 
> 
> 
> 
> 

Ticket Details
===================
Ticket ID: WYC-198714
Department: Support IDV
Priority: Emergency
Status: Open