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Message: Re: High CAPE Values
Posted by John M. Brown on 20 Jul 02, 20:21 MT, in response to High CAPE Values, posted by Eric Nelson on 20 Jul 02, 19:18 MT
Yes, these are extraordinary CAPE values. I notice that
the METAR observations, Ern IA and sern MN especially,
are rptg dew pts in the upper 70s to even mid 80s F.
This is the best example of buildup in sfc dew points
(and by implication, sfc theta-e values, up to about
380K!!) that I have seen in several years--about as good as
it gets, and certainly much better than over the oceanic
tropics, except in the core of a tropical cyclone!
When such abundant values of moisture exist, the CAPE
calculations become very sensitive to the mixing ratio
of the lifted parcel (nonlinearity of the Clausius-Clapeyron
eqn) and the assumptions made in the calculations
(particularly, the form of the first law of thermo,
and the form of the Clausius-Clapeyron eq for saturation
vapor pressure as function of the temperature).
The Eta and RUC differ in these assumptions,
with the RUC's assumptions tending to favor larger
CAPE when dew points are high.
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