[ncl-talk] wrf cape oddities

[Jon Meyer]

Good day everyone,

I've been using the wrf_user_getvar to extract max CAPE values and I'm
seeing large regions filled with missing values. Under the hood, the getvar
function is simply performing the necessary variable I/O and conversion to
correct units, which are then passed into the wrf_cape_2d function.

The documentation of the wrf_cape_2d function states "*Previous to version
6.1.0 <https://www.ncl.ucar.edu/prev_releases.shtml#6.1.0>**, this function
returned a value of -0.1 for out-of-range values. This has been replaced
with a missing value, and a "_FillValue" attribute is also set.*"

I added some print statements to the getvar function to peek at the arrays
being passed into the wrf_cape_2d function and there are no missing values
in any of the arrays, and the min/max range is appropriate for all arrays*,
yet the cape values returned have large regions of missing (although lots
of reasonable CAPE values are returned). The min value of CAPE that is
returned is 0.1, so I'm curious about whether the missing values should be
set to zero values, or left as missing, which will impact subsequent
analysis.

I'm wondering what the out-of-range values represent physically? What
causes an out-of-range value, as opposed to a small value such as the 0.1's
that are being returned. Without being able to crack open the wrf_cape_2d
function, I'm hoping someone with experience there can chime in.

Thanks in advance,
Jon

*As a side note, the documentation for wrf_cape_2d states the PSFC field
needs to be in hPa. The getvar function looks to be passing in Pa but with
reasonable CAPE fields returned, I'm guessing there is some login in the
wrf_cape_2d function that sets correct units. I tested by changing the
units from Pa to hPa as the documentation requests, and the number of
missing values being returned increases, so something goofy is going on
that I'm not able to see unless I can crack open the wrf_cape_2d function
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