A new automated method to retrieve charge layer polarity from flashes, named Chargepol, is presented in this paper. Using data from the NASA Lightning Mapping Array (LMA) deployed during the RELAMPAGO field campaign in Cordoba, Argentina, from November 2018 to April 2019, this method estimates the polarity of vertical charge distributions and their altitudes and thicknesses (or vertical depth) using the very-high frequency (VHF) source emissions detected by LMAs. When this method is applied to LMA data for extended periods of time, it is capable of inferring a storm’s bulk electrical charge structure throughout its life cycle. This method reliably predicted the polarity of charge within which lightning flashes propagated and was validated in comparison to methods that require manual assignment of polarities via visual inspection of VHF lightning sources. Examples of normal and anomalous charge structures retrieved using Chargepol for storms in Central Argentina during RELAMPAGO are presented for the first time. Application of Chargepol to five months of LMA data in Central Argentina and several locations in the United States allowed for the characterization of the charge structure in these regions and for a reliable comparison using the same methodology. About 13.3% of Cordoba thunderstorms were defined by an anomalous charge structure, slightly higher than in Oklahoma (12.5%) and West Texas (11.1%), higher than Alabama (7.3%), and considerably lower than in Colorado (82.6%). Some of the Cordoba anomalous thunderstorms presented enhanced low-level positive charge, a feature rarely if ever observed in Colorado thunderstorms.

The lightning data products generated by the Low-Frequency (LF) radio lightning locating system (LLS) deployed during the RELAMPAGO field campaign in Argentina provide a valuable dataset to research the lightning evolution and characteristics of convective storms that produce high-impact weather. LF LLS datasets offer a practical range for mesoscale studies, allowing for the observation of lightning characteristics of storms such as Mesoscale Convective Systems (MCSs) or large convective lines that travel longer distances which are not necessarily staying in range of regional VHF-based lightning detection systems throughout their lifetime. LF LLSs also provide different information than optical space-borne lightning detectors. Lightning measurements exclusive to LF systems include discharge peak current, lightning polarity, and lightning type classification based on the lightning-emitted radio waveform. Furthermore, these measurements can provide additional information on flash rates (e.g. positive CG flash rate) or Narrow Bipolar Events (NBE) which may often be associated with dynamically intense convection. In this paper, the geolocation and data processing of the LF dataset collected during RELAMPAGO is fully described and its performance characterized, with location accuracy better than 10 km. The detection efficiency (DE) of the dataset is compared to that of the Geostationary Lightning Mapper (GLM), and spatiotemporal DE losses in the LF dataset are discussed. Storm case-studies on November 10, 2018, highlight the strengths of the dataset, which include robust flash clustering and insightful flash rate and peak current measures, while illustrating how its limitations, including DE losses, can be managed.