The influence of supersaturation at low rime accretion rates on thunderstorm electrification from field-independent graupel-ice crystal collisions

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

“…In particular, the effects of dry air on supersaturation and its theorized impact on the relative growth and associated charging of riming and nonriming hydrometeors should be considered (e.g., Lang & Rutledge, 2002). Results from limited laboratory studies and theoretical analyses have found that the degree of environmental supersaturation may play a role in the polarity of graupel charging in addition to cloud LWC (Berdeklis & List, 2001; Emersic & Saunders, 2020; Mitzeva et al, 2005; Saunders et al, 2006; Tsenova et al, 2010). If cloud supersaturation is an additional factor in the observed polarity of charging hydrometeors and resultant net charge regions, it may explain some variation observed in environmental parameters between interregional ACSs in addition to ACS development despite competing environmental influences on mixed‐phase LWC.…”

“…Results from laboratory studies indicate that graupel (ice crystals) typically charge negatively (positively) during ice‐ice collisional NIC, though with increased LWC and/or temperatures warmer than −10°C, graupel (ice crystals) instead charge positively (negatively) as a result of increased riming efficiency (Berdeklis & List, 2001; Jayaratne et al, 1983; Saunders et al, 2006; Takahashi, 1978). Analytical models and limited results from laboratory studies have suggested that supersaturation may play an additional role in the polarity of particles charging by NIC (Emersic & Saunders, 2020; Mitzeva et al, 2005; Saunders et al, 2006; Tsenova et al, 2010). Once particle‐scale charging has taken place, gravitational sedimentation and differential advection of charged particles by kinematic processes at the storm to turbulent scales result in accumulated charged hydrometeors and net charge regions (e.g., Bruning & MacGorman, 2013; Lhermitte & Williams, 1985; Williams, 1985).…”

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

“…In the anomalous supercells, maximum updraft speeds were either aligned with or located above the dominant positive charge region and extended into the glaciated region. At these temperatures, collisional NIC involving riming hydrometeors would have been inactive as a result of homogeneous freezing (although studies have shown that some amount of charging may occur in the absence of LWC, e.g., Dye & Bansemer, 2019; Emersic & Saunders, 2020; Mitzeva et al., 2006). Therefore, the most likely region of positive charging of riming hydrometeors did not strictly coincide with storm maximum updraft speeds, as similarly observed by Chmielewski et al.…”

“…Laboratory studies have shown that the magnitude and polarity of charge transfer are controlled by the velocity of the particle collisions, riming rate associated with effective LWC, ice crystal and cloud water size spectra, and cloud and particle temperatures (Avila & Pereyra, 2000; Emersic & Saunders, 2010; Jayaratne et al., 1983; Saunders & Peck, 1998; Saunders et al., 2006), pointing to the importance of riming efficiency in enhancing the depositional growth rate and positive charging of graupel (e.g., B. Baker et al., 1987; Mitzeva et al., 2005; Saunders et al., 2006). Limited laboratory studies have also suggested that some of the discrepancies in LWC and reversal temperature at which positive charging rather than negative charging was observed may have resulted from unaccounted variations in supersaturation (e.g., Berdeklis & List, 2001; Emersic & Saunders, 2010, 2020; Saunders et al., 2006). Theoretical models also indicate that the saturation ratio influences the growth of small ice relative to graupel such that graupel charges positively at lower values of effective LWC in the presence of reduced supersaturation (Mitzeva et al., 2005; Saunders et al., 2001; Tsenova et al., 2010).…”

Global Lightning Quanta

“…The general trend is that the majority of lightning flashes occur in the tropics as a result of deep convection driven by the pole to equator temperature increase and the Clausius Clapeyron equation (e.g., Price, 2000; Williams, 1994, Section 4d) that describes the phase transition between water vapor and liquid water content in the boundary layer. The Clausius Clapeyron equation also describes the coexistence curves of phase transitions near the triple point of water in the mixed phase region of thunderclouds which are of critical importance for the electrical charging and subsequent dielectric breakdown of air in the form of lightning flashes to occur (Emersic & Saunders, 2020; Saunders et al., 1991). However, research in this arena tackles in essence three atmospheric variables, (1) the atmospheric temperature which leads to charge separation in thunderclouds, (2) the resulting lightning flash occurrence frequency, and (3) the electromagnetic waves produced by the lightning discharges.…”