y\centerline {\bf Role of Stratospheric Air in a Severe Weather 
        Event</TITLE></HEAD>

<P> <H2>Evidence of upper tropospheric rapid PV fluctuations due to diabatic and diffusive processes</H2> </p>

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<p> <h3>Melissa A. Goering (1), William A. Gallus, Jr.(1) and John L Stanford</h3>


<p>(1) Department of Geological & Atmospheric Sciences, Iowa State University, Ames, Iowa 50011</p>


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<p>
(submitted to J. Geophys. Rev.)
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<p>
<h3>
Abstract
</h3>

</p>

Diabatic and diffusive processes are examined in a region having
higher values of total column ozone with an apparent loss of potential
vorticity (PV) in a severe thunderstorm event associated with a deep
tropopause fold over central Nebraska on May 15, 1998.  Earth Probe
Total Ozone Mapping Spectrometer (EP/TOMS) total ozone data, NCEP Eta
model output, and Rapid Update Cycle (RUC) analyses are used to
examine the event.  Backward trajectories reveal complex processes
aiding in the production and destruction of PV.  Parcel trajectories
in the upper levels imply PV generation due to jet streak dynamics.
These upper-level parcels experience a large increase in PV from
tropospheric to stratospheric values.  Shortly thereafter, PV
decreases markedly due to diabatic effects.  Lower-level parcels are
influenced by both diffusive and diabatic effects.  These parcels
acquire stratospheric values of PV while on the cyclonic shear side of
a jet streak.  As they ascend, their PV increases due to latent heat
release while below the level of maximum heating.  These parcels also
experience rapid destruction of PV after they ascend above the level
of peak diabatic heating.  The rapid changes in PV raise questions
about possible cross-tropopause exchange.  These results corroborate
earlier work suggesting that parcel PV can undergo sizeable changes,
both increases and decreases, as parcels traverse a baroclinic system.
The results have significance for tropospheric-stratospheric exchange
studies: isentropic PV alone is an insufficient indicator of air mass
origin and should be used in conjunction with chemical tracers such as
ozone or water vapor.

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