[ncl-talk] Computing cape

[Andrew Kren - NOAA Affiliate]

Dear ncl-talk,

I am computing CAPE using the ncl function wrf_cape_2d.

I am computing this for the ERA-5 reanalysis dataset and my output GFS
forecast files. When I compute the CAPE for both datasets, I get some
comparable values between the two datasets, but also some differences. The
most striking example is over the mountains, such as the Himalayas, where
ERA5 has no cape, but GFS exceeds 6000 J/kg.

I did some examining to see what this was and plotted the vertical plot of
temperature for ERA5 and GFS over that mountain area. Turns out that GFS
has a higher lapse rate below 600 mb compared to ERA5.

I guess my question is, would there be any way to rectify this? I could
mask values below the surface, but then the function would not account for
missing values, correct? Or should I use the GFS derived CAPE (which
doesn't have any cape over the Tibetan plateau).

Any ideas or suggestions are appreciated.

Thanks,

-- 
Andrew Kren
Assistant Scientist
CIMAS & NOAA/AOML
325 Broadway, Boulder, CO 80305
(303) 497-5418
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