In this study, it is hypothesized that the mesoscale environment can indirectly
control the cloud-to-ground (CG) lightning polarity of severe storms by directly
affecting their structural, dynamical, and microphysical properties, which in turn directly
control cloud electrification and CG flash polarity. A more specific hypothesis, which
has been supported by past observational and laboratory charging studies, suggests that
broad, strong updrafts and associated large liquid water contents in severe storms lead to
enhanced positive charging of graupel and hail via the noninductive charging
mechanism, the generation of an inverted charge structure, and increased positive CG
lightning production. The corollary is that environmental conditions favoring these
kinematic and microphysical characteristics should support severe storms generating an
anomalously high (> 25%) percentage of positive CG lightning (i.e., positive storms),
while environmental conditions relatively less favorable should sustain storms
characterized by a typical (≤ 25%) percentage of positive CG lightning (i.e., negative
storms).
Forty-eight inflow proximity soundings were analyzed to characterize the
environments of nine distinct mesoscale regions of severe storms (four positive and five
negative) on six days during May - June 2002 over the central United States. This analysis clearly demonstrated significant and systematic differences in the mesoscale
environments of positive and negative storms, which were consistent with the stated
hypothesis. When compared to negative storms, positive storms occurred in
environments associated with a drier low to midtroposphere, higher cloud base height,
smaller warm cloud depth, stronger conditional instability, larger 0-3 km AGL wind
shear, stronger 0-2 km AGL storm-relative wind speed, and larger buoyancy in the
mixed-phase zone, at a statistically significant level. Differences in the warm cloud
depth of positive and negative storms were by far the most dramatic, suggesting an
important role for this parameter in controlling CG lightning polarity. Subjective visual
inspection of radar imagery revealed no strong relationship between convective mode
and CG lightning polarity, and also illustrated that positive and negative severe storms
can be equally intense.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/85783 |
| Date | 10 October 2008 |
| Creators | Buffalo, Kurt Matthew |
| Contributors | Carey, Lawrence D. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, born digital |
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