Date of Award
2020
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Atmospheric and Earth Science
Committee Chair
Lawrence D. Carey
Committee Member
Daniel J. Cecil
Committee Member
Kevin R. Knupp
Committee Member
Edward R. Mansell
Committee Member
Udaysankar S. Nair
Subject(s)
Atmospheric electricity, Lightning, Severe storms, Thunderstorms, Convection (Meteorology)
Abstract
This research is concerned with two supercell thunderstorms observed in the Southeastern United States that exhibited anomalous charge structures (ACSs). ACSs are characterized by an apparent reversal of dominant charge region polarity from normal charge structures (NCSs). Historically, ACSs have been rarely indicated within the Southeast and are not documented within the literature. Conceptual models of ACSs more typically observed in the Great Plains hypothesize that ACSs arise as a result of high liquid water content (LWC) in the mixed-phase region of an updraft, facilitated by conditions that increase the efficacy of the updraft in supplying LWC and reduce the efficiency of warm precipitation processes, including via increased aerosols. The lack of ACS observations in the Southeast has been attributed to regional climatic incongruence with these conditions. Total lightning observations, dual-polarization Doppler weather radar data, and environmental model analyses were used to assess the applicability of hypotheses concerning the electrical, microphysical, and kinematic structures of the supercells within which ACSs were observed (i.e., anomalous supercells) in the Southeast. Consistent with ACS conceptual models, dominant positive (negative) charge regions were observed at lower (upper) levels in precipitation ice (ice crystals). However, with the exception of decreased relative humidity, many observed environmental conditions were inconsistent with documented anomalous storms. In a subsequent study in which the Southeastern anomalous supercells were contrasted with two comparable Southeastern supercells exhibiting NCSs, anomalous supercells had faster, deeper mixed-phase updrafts and contained more precipitation ice. Many environmental conditions associated with LWC did not substantially contrast and all storms exhibited similar metrics of warm precipitation efficiency. Observed lower relative humidity in ACS environments suggested that dry air may have been important to anomalous charging. The evolution and spatial characteristics of lightning properties were contrasted between an anomalous and normal supercell. In the anomalous supercell, both charge polarities were more closely associated with precipitation ice and lightning flashes were more frequently observed in fast updrafts. Lightning flashes were increasingly observed in the updraft of the anomalous supercell as its negative charge region became increasingly collocated with precipitation ice, suggesting a correspondence between charge region microphysics and spatial flash characteristics.
Recommended Citation
Stough, Sarah M., "Characterization of supercell thunderstorms exhibiting anomalous charge structures in the Southeastern United States" (2020). Dissertations. 394.
https://louis.uah.edu/uah-dissertations/394