Observations of Anomalous Charge Structures in Supercell Thunderstorms in the Southeastern United States

Abstract

Anomalous thunderstorm charge structures (ACSs), characterized by a dominant layer of positive charge in the lower mixed‐phase region, are uncommon and rarely reported outside of the Great Plains region of the United States. This study documents the kinematics, precipitation microphysics, and charge structures of two supercell thunderstorms exhibiting ACSs that were observed in the Southeastern United States. Ground‐based three‐dimensional total lightning observations, polarimetric Doppler radar observations, and environmental model analysis of these supercells presented the opportunity to evaluate conceptual models of ACS development and characteristics in an atypical parameter space. In both anomalous storms, prominent layers of positive charge were located in lower to middle mixed‐phase regions (−10°C to −30°C) of updrafts and were spatially associated with riming hydrometeor types. Simultaneously, negative charge regions were identified above the primary positive charge layers in the upper mixed‐phase and glaciated region of updrafts, collocated with graupel and small ice hydrometeors. While coarse charge structure observations were consistent with noninductive charging‐based models of anomalous storms, charge structure complexities were also observed that suggested variability in cloud microphysical conditions. Analysis of the environments in which these storms formed indicated that several parameters thought to increase mixed‐phase liquid water content in favor of anomalous charging were inconsistent with those documented in the Great Plains region. However, environmental humidity metrics were most comparable. Comparisons between these and other documented anomalous storms identified similarities in kinematic structure and microphysical conditions while motivating ongoing study of the environmental parameter space supportive of ACSs.

Characterizing Charge Structure in Central Argentina Thunderstorms During RELAMPAGO Utilizing a New Charge Layer Polarity Identification Method

“…The general charge structure is estimated for a large dataset with a new algorithm, allowing for the inference of the likelihood of normal and anomalous charge structure. Similar to Tessendorf et al (2007b) and Stough and Carey (2020), this method automatically infers charge polarity from flashes, more closely resembling Tessendorf et al (2007b) method but with improved procedures, better emulating the steps that a human expert would perform when assigning polarity to LMA sources for a flash by detecting the negative leader in a bi-directional model and assigning polarity to sources of a flash (e.g., Rust et al 2005). In this study, if a given lightning flash passes a series of conditions, an algorithm analyzes its source location and time in order to produce a prediction of charge layer polarity for that flash.…”

“…Thunderstorms with upper-level negative and mid-level positive charge layers define an anomalous charge structure, as observed in thunderstorms during the STEPS field campaign conducted in Kansas, Colorado, and Nebraska (MacGorman et al, 2005;Rust et al, 2005;Rust & MacGorman, 2002;Tessendorf et al, 2007a;Tessendorf et al, 2007b;Weiss et al, 2008;Wiens et al, 2005). They have also been observed in thunderstorms in Oklahoma by Marshall et al (1995) and Emersic et al (2011), during the TELEX field campaign (MacGorman et al, 2008), in Texas (Chmielewski et al, 2018), Alabama (Stough & Carey, 2020), and Spain (Pineda et al, 2016). Storms with a normal charge structure would have a dominant net negative charge in the mixed-phase layer, and net positive above, as demonstrated in early foundational studies reviewed by Williams (1985), in the in-situ aircraft studies by Dye et al (1986Dye et al ( , 1988Dye et al ( , 1989, during TELEX (Bruning et al, 2007) and STEPS (Weiss et al, 2008) field campaigns, among others.…”

Examining Conditions Supporting the Development of Anomalous Charge Structures in Supercell Thunderstorms in the Southeastern United States

“…R. Williams, 1985). The details of this charge classification method and how it compares with more traditional techniques are described in Stough and Carey (2020). Briefly, DBSCAN was implemented to identify clusters of VHF sources apart from isolated VHF sources in standardized temporal and altitudinal space.…”

“…10.1029/2021JD034582 10 of 31 negative charge layers were more diffuse in the anomalous April 22, 2017 supercell, suggesting charge structure complexity arising from vertical overlap in charge regions and horizontal charge region heterogeneity (Stough & Carey, 2020).…”

“…The charge layers in the anomalous April 10, 2009 supercell exhibited more vertical variation over time than was observed in the other storms. Initiation and development through approximately 1739 UTC were captured during the analysis period of the April 10, 2009 storm whereas all other storms were analyzed after they had already reached maturity (Stough & Carey, 2020). As the updraft developed in the April 10, 2009 supercell, the flash rate increased (Schultz et al, 2015(Schultz et al, , 2017 and the net charge layers associated with charged hydrometeor populations were lofted to higher altitudes within the storm (Stough & Carey, 2020).…”