Insight into the Kinematic and Microphysical Processes that Control Lightning Jumps

Abstract

A detailed case study analysis of four thunderstorms is performed using polarimetric and multi-Doppler capabilities to provide specificity on the physical and dynamical drivers behind lightning jumps. The main differences between small increases in the total flash rate and a lightning jump are the increases in graupel mass and updraft volumes ≥10 m s−1 between the −10° and −40°C isotherms. Updraft volumes ≥10 m s−1 increased in magnitude at least 3–5 min in advance of the increase in both graupel mass and total flash rate. Updraft volumes ≥10 m s−1 are more robustly correlated to total flash rate than maximum updraft speed over a thunderstorm’s entire life cycle. However, peak updraft speeds increase prior to 8 of the 12 lightning jumps examined. Decreases in mean and median flash footprint size during increases in total lightning are observed in all four thunderstorms and are most notable during development stages within the most intense storms. However, this inverse relationship breaks down on larger storm scales as storms mature and anvils and stratiform regions developed with time. Promisingly, smaller flash sizes are still collocated with the strongest updraft speeds, while larger flash sizes are observed within weaker updraft regions. The results herein emphasize the following for lightning jump applications: both the lightning jump sigma level and the resultant magnitude of the total flash rate must be employed in conjunction to assess storm intensity using lightning data. The sigma-level magnitude of the lightning jump is the early warning that indicates that rapid intensification is occurring, while the magnitude of the total flash rate provides insight into the size and maintenance of the updraft volume and graupel mass. These cases serve as conceptual models for future applications of the lightning jump algorithm for hazardous weather monitoring.

Electrical discharges in the overshooting tops of thunderstorms

“…This is consistent with the observation by Schultz et al . [] that mean flash sizes tended to be smaller during relatively large increases in total flash rates as storms intensified and to be larger when updrafts were weakening.…”

Variations of Thunderstorm Charge Structures in West Texas on 4 June 2012

“…Large flash rates and small flash sizes have been associated with strong updrafts (Chronis et al, ; Schultz et al, , ), but no statistical difference was observed in the average storm flash rate or size between the anomalously and normally electrified storms. As expected (e.g., Lang & Rutledge, ), normally charged storms did have maximum VHF source densities at higher altitudes than the anomalously charged storms by 0.92 km, coinciding with observations of the largest VHF source density in +CG‐ and −CG‐dominated storms near −30 °C and −40 °C (8.8 and 10 km MSL in this case), respectively.…”

“…From a forecasting perspective assimilating total lightning observations to nudge model initial conditions can improve short‐term simulations (Fierro et al, , ). On the storm scale, a statistically large increase in total flash rate, known as a lightning jump, can indicate changes in the storm updraft which can further correlate with severe weather production (Schultz et al, , ; Chronis et al, ). The flash distribution can portray structural information similar to how common storm characteristics are described through radar observations.…”

Lower Ionospheric Conductivity Modification Above a Thunderstorm Updraught

“…This pattern of lightning activity is reflected in both the radio receiver and the BTD-300 data (Figure 4c) where the frequency of spikes roughly match the reported lightning frequency (cf. This increase in IC activity is associated with strengthening thunderstorm updraughts (e.g., Schultz et al, 2015;Williams et al, 1989). This increase in IC activity is associated with strengthening thunderstorm updraughts (e.g., Schultz et al, 2015;Williams et al, 1989).…”