This study characterizes Lightning Mapping Array performance for networks that participated in the Deep Convective Clouds and Chemistry field program using new Monte Carlo and curvature matrix model simulations. These open‐source simulation tools are readily adapted to real‐time operations or detailed studies of performance. Each simulation accounted for receiver threshold and location, as well as a reference distribution of source powers and flash sizes based on thunderstorm observations and the mechanics of station triggering. Source and flash detection efficiency were combined with solution bias and variability to predict flash area distortion at long ranges. Location errors and detection efficiency were highly dependent on the station configuration and thresholds, especially at longer ranges, such that performance varied more than expected across different networks and with azimuth within networks. Error characteristics matched prior studies, which led to an increase in flash distortion with range. Predicted flash detection efficiency exceeded 95% within 100 km of all networks.

This study documents an environment for which small changes therein significantly impacted electrification and for which current theories of electrification lacked the ability to discriminate storm polarity. Thirty single‐cell and multicell storms from 1900 to 2200 UTC on 4 June 2012 over a 150‐ by 100‐km West Texas region were examined. Some of these storms had anomalous charge structures (primarily positive charge in the midlevels at −10 °C to −30 °C or 6.3 to 8.8 km above MSL locally) and some normal (primarily negative at midlevels), even though they existed concurrently and did not statistically differ in overall flash sizes, flash rates, radar volume, or echo top height. Overall, the normal storms ingested lower equivalent potential temperature surface air and were estimated to experience lower convective available potential energy than the anomalous storms, as observed in other studies. They were, however, estimated to have smaller warm cloud depth and surface dew point temperatures, contrary to expectations. Significant overlap between the storm environments suggested that lower instability may have contributed to some storms becoming normally electrified, but it was not a sufficient condition. Additionally, there had been previous convection in the region dominated by normal‐polarity storms. A Weather Research and Forecasting ensemble suggested that the previous convection moistened the midlevels of the atmosphere near cloud base. We propose that future studies investigate dry‐air entrainment as an additional, intertwined environmental factor that could decrease droplet sizes and effective warm rain processes, promoting positive graupel charging in the midlevels and anomalous charge structures.

As lightning-detection records lengthen and the efficiency of severe weather reporting increases, more accurate climatologies of convective hazards can be constructed. In this study we aggregate flashes from the NLDN and ATDnet lightning-detection networks with severe weather reports from ESWD and SPC Storm Data on a common grid of 0.25° and 1-hour steps. Each year approximately 75–200 thunderstorm hours occur over the southwestern, central and eastern United States, with a peak over Florida (200–250 hours). The activity over the majority of Europe ranges 15–100 hours, with peaks over Italy and mountains (Pyrenees, Alps, Carpathians, Dinaric Alps; 100–150 hours). The highest convective activity over continental Europe occurs during summer and over the Mediterranean during autumn. The United States peak for tornadoes and large hail reports is in spring, preceding the maximum of lightning and severe wind reports by 1–2 months. Convective hazards occur typically in the late afternoon, with the exception of the Midwest and Great Plains, where mesoscale convective systems shift peak lightning threat to the night. The severe wind threat is delayed by 1–2 hours compared to hail and tornadoes. The fraction of nocturnal lightning over land ranges 15%–30% with lowest values observed over Florida and mountains (∼10%). Wintertime lightning shares the highest fraction of severe weather. Compared to Europe, extreme events are considerably more frequent over the United States, with maximum activity over the Great Plains. However, the threat over Europe should not be underestimated, as severe weather outbreaks with damaging winds, very large hail and significant tornadoes occasionally occur over densely populated areas.

Lightning Mapping Arrays (LMAs) detect very high frequency (VHF) radiation produced by lightning as it propagates; however, VHF source detection efficiency drops off rapidly with range from the centers of the arrays, which results in a maximum of source points over the center of the network for large datasets. Using data from nearly one billion detected sources of various powers, an approximation of VHF source detection efficiency (relative to the number of sources detected within 25 km of the center of the array) for the Oklahoma LMA is calculated for different ranges and source powers. The calculated source detection efficiencies are then used to normalize the VHF source data out to a range of 125 km, as a method for correcting the detection efficiency drop-off with range. The data are also sorted into flashes using a popular flash-sorting algorithm in order to compare how well flash sorting corrects for detection efficiency drop-off with range compared to the normalization method. Both methods produce similar patterns and maxima of the lightning location, but the differences between them are identified and highlighted. The use of a flash-sorting algorithm is recommended for future studies involving large sets of data.

Occasionally, lightning will exit the top of a thunderstorm and connect to the lower edge of space, forming a gigantic jet. Here, we report on observations of a negative gigantic jet that transferred an extraordinary amount of charge between the troposphere and ionosphere (∼300 C). It occurred in unusual circumstances, emerging from an area of weak convection. As the discharge ascended from the cloud top, tens of very high frequency (VHF) radio sources were detected from 22 to 45 km altitude, while simultaneous optical emissions (777.4 nm OI emitted from lightning leaders) remained near cloud top (15 to 20 km altitude). This implies that the high-altitude VHF sources were produced by streamers and the streamer discharge activity can extend all the way from near cloud top to the ionosphere. The simultaneous three-dimensional radio and optical data indicate that VHF lightning networks detect emissions from streamer corona rather than the leader channel, which has broad implications to lightning physics beyond that of gigantic jets.

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A developing supercell storm on 29–30 May 2012 in north‐central Oklahoma was observed with the Oklahoma Lightning Mapping Array (OKLMA) and three mobile radars. The storm's vertical charge structure inferred from the OKLMA was anomalous overall but varied considerably even within 10 km of the bounded weak echo region (BWER) and the bounded weak lightning region (BWLR) or lightning hole. Near the BWER, three distinct charge structures were observed—an inverted dipole, an inverted tripole, and a bottom‐heavy normal tripole. One column within each structure was analyzed relative to the Doppler‐derived wind field and environmental properties derived by a diabatic Lagrangian analysis (DLA). Within each column, back trajectories of graupel and hail particles additionally illustrate the history of the diagnosed in‐cloud microphysical properties, which are expected to influence noninductive electrification and may have contributed to the observed charge profiles. This study objectively demonstrates the complicated scenarios presented by the three‐dimensional motions around and through the updraft and provides likely constraints on how each of the three distinct vertical charge distributions could have been produced within this focused region of the storm.

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