Isentropic surface plots with WRF output

Hi, the semester is just about done, so I'm back...

We're trying to produce some plots of pressure, humidity
and wind on isentropic surfaces from our WRF model output.

I found an NCL example at:

<http://www.ncl.ucar.edu/Applications/isent.shtml>

and have tried to apply the methods to our own
situation. I've simplified the script as much as I could
for this problem statement, and it's available at

<http://weather.arsc.edu/Miscellaneous/NCL/IsentropicSurface/wrfIsentropic-P.ncl>

The input data, "wrfoutd02.nc" is also in that directory

<http://weather.arsc.edu/Miscellaneous/NCL/IsentropicSurface/wrfoutd02.nc>

The output image produced by this script/data is at

<http://weather.arsc.edu/Miscellaneous/NCL/IsentropicSurface/A.jpg>

The problem is that the plot is full of "no" values. This is
understandable where the theta surface might run into the
terrain, but not over the ocean. At the very least, if our theta
surface was starting to collide with the ocean surface, we would
expect to see pressures of around 1000mb in those areas.
But, as you can see, we just have a lot of "missing" data.

In my script, I've printed out ALL the pressure values on the theta
surface (pf_xlvl), and there are lots of values of 1+e36, which strikes
me as some sort of numerical issue. Just for the heck of it, at one of
those points (9, 370), I've printed out the column of values for theta
and pressure, and those values look good. This debugging output
(2+ Mbytes) is available at

<http://weather.arsc.edu/Miscellaneous/NCL/IsentropicSurface/t.out>

One of the meteorologists who's looked at the output feels that the
areas that "are" plotted look reasonable, but we can't explain all those
missing values.

I have to admit that I'm kind of out of my league on this one. I've had
some thoughts that the NCL example referenced above might assume
data on pressure levels, whilst the stuff I'm working with is terrain-following,
but if it's really just a simple interpolation function, maybe that shouldn't
matter?

I feel like I'm just "black-boxing" my use of int2p(), so could easily be
missing something very fundamental...

Thanks for listening!

Don Morton

-- 
University of Montana
http://www.cs.umt.edu/~morton/
Arctic Region Supercomputing Center
http://weather.arsc.edu/
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