Weather and Climate Systems

Charge Structure and Lightning Patterns in Simulated Mesoscale Convective Systems

Allison Silveira

School of Meteorology

09 December 2015, 3:00 PM

National Weather Center, Room 5930
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Observations of charge structure within the stratiform region of a mesoscale convective
system (MCS) repeatedly reveal quasi-steady, horizontal charge layers at and above
the melting level. Previous studies have suggested charge advection can explain the
uppermost layers as charged ice particles are ejected from the convective line into the
weaker downdrafts of the transition zone. These sloping layers have been observed to
persist beyond the transition zone into the weak, broad mesoscale updrafts of the
stratiform region. Likewise, in the layer below -10°C through the melting level, significant
charge densities are consistently observed, yet are apparently independent of the
convective line. This study examined the contribution of several “alternate” charge
separation processes to the generation and maintenance of charge layers near the
melting level. A high-resolution, three-dimensional model using full dynamics with twomoment
microphysics was employed. The microphysics were improved to include the
prediction of liquid water fractions on graupel and snow to better parameterize the
hypothetical charge separation mechanisms.

The model solutions exhibited similar structure to the standard conceptual model of a
leading-line, trailing stratiform MCS with respect to observed kinematics, microphysics,
and charge structure. Unlike the two-dimensional counterpart, charge advection did not
account for any charge beyond the transition zone. The tests showed, however, the
current selection of electrification processes and microphysical parameterizations failed
to reproduce the observed charge layers in the stratiform region.