2.4 Characterizing Lightning's Response to the Spatial Distribution of Updraft Microphysics

Tuesday, 8 January 2019: 9:15 AM
North 225AB (Phoenix Convention Center - West and North Buildings)
Sarah M. Stough, Univ. of Alabama in Huntsville, Huntsville, AL; and L. D. Carey, C. J. Schultz, and D. J. Cecil

Recent work has continued to refine understanding of connections between lightning and the mixed-phase updraft to facilitate more meaningful interpretation of lightning in the context of convective intensity. Related efforts have further defined the physical basis of the lightning jump, establishing that the rapid increase in flash rate during a lightning jump is a physical response to substantial intensification of the updraft. Specifically, properties such as the 10 m s-1 updraft volume and maximum updraft speeds have been shown to increase by four to five times in magnitude during lightning jumps compared with smaller changes associated with regular flash rate increases. However, while this quantified response in lightning to thunderstorm intensification generally relates lightning jump occurrence to subsequent observations of high-impact phenomena, the lightning jump does not readily indicate specific severe weather processes nor are lightning jumps and severe events always associated.

The lightning jump serves as an application and extension of generally well-correlated relationships between bulk mixed-phase updraft properties and lightning flash rates. However, variability and inconsistencies in these flash rate relationships have been reported, likely contributing to documented inconsistencies in lightning jump observations. By definition, flash rate-based metrics such as the lightning jump only account for the number of flashes that occur and how that number changes in time. They do not inform about flashes properties and associated local storm characteristics that influence them, though this information may be useful for interpretation of local convective processes. For instance, thunderstorm charge regions are related to spatial distributions of microphysical properties which are also known to respond to kinematic influence. It has also been observed that flash properties relate to charge structure, indicating that the microphysical response to updraft evolution is important to how flash properties are interpreted with respect to the kinematics. Better understanding of the local microphysical details of the mixed-phase updraft will add value to how lightning data may be interpreted and used, as well as allow for continued work in understanding specifics of the relationships between lightning, convective processes, and thunderstorm intensity.

Complex connections between lightning, updraft kinematics and microphysics require analysis of both temporal and three-dimensional spatial components of lightning properties. Data from approximately 15 well-sampled storms are used to address these connections, with primary goals of addressing microphysical controls on lightning initiation and propagation location, variability of microphysical distribution associated with lightning flash structure, and how the distribution of microphysical properties relates to kinematics. These topics are investigated using spatial analysis of lightning properties and charge structure from lightning mapping array data as well as radar-based observations of updraft structure, hydrometeors, and precipitation processes. While the number of supercells considered allows for statistical analysis, a smaller subset is presented in detail alongside statistical results to illustrate and facilitate deeper discussion of consistent relationships as well as observed discrepancies and associated challenges. These results will also aid in directing planned hypothesis testing of microphysics-based relationships using an idealized numerical model equipped with electrification parameterizations. Results from these detailed spatial analyses are also discussed as relevant to continuing work characterizing lightning jump dependency on kinematic and microphysical characteristics of the updraft and implications for inferences of intensity.

- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner