Transient luminous events above two mesoscale convective systems: Storm structure and evolution
Abstract
Two warm-season mesoscale convective systems (MCSs) were analyzed with respect to
their production of transient luminous events (TLEs), mainly sprites. The 20 June
2007 symmetric MCS produced 282 observed TLEs over a 4 h period, during which the
storms intense convection weakened and its stratiform region strengthened. TLE production
corresponded well to convective intensity. The convective elements of the MCS contained
normal-polarity tripole charge structures with upper-level positive charge (-40°C),
midlevel negative charge (-20°C), and low-level positive charge near the melting level.
In contrast to previous sprite studies, the stratiform charge layer involved in TLE
production by parent positive cloud-to-ground (+CG) lightning resided at upper levels.
This layer was physically connected to upper-level convective positive charge via
a downward sloping pathway. The average altitude discharged by TLE-parent flashes
during TLE activity was 8.2 km above mean sea level (MSL; -25°C). The 9 May 2007 asymmetric
MCS produced 25 observed TLEs over a 2 h period, during which the storms convection
rapidly weakened before recovering later. Unlike 20 June, TLE production was approximately
anticorrelated with convective intensity. The 9 May storm, which also had a normal
tripole in its convection, best fit the conventional model of low-altitude positive
charge playing the dominant role in sprite production; however, the average altitude
discharged during the TLE phase of flashes still was higher than the melting level:
6.1 km MSL (-15°C). Based on these results, it is inferred that sprite production
and sprite-parent positive charge altitude depend on MCS morphology. Copyright 2010
by the American Geophysical Union.
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Show full item recordScholars@Duke
Steven A. Cummer
William H. Younger Distinguished Professor of Engineering
Dr. Steven Cummer received his Ph.D. in Electrical Engineering from Stanford University
in 1997 and prior to joining Duke University in 1999 he spent two years at NASA Goddard
Space Flight Center as an NRC postdoctoral research associate. Awards he has received
include a National Science Foundation CAREER award and a Presidential Early Career
Award for Scientists and Engineers (PECASE) in 2001. His current work is in a variety
of theoretical and experimental electromagnetic problems related to g

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