ABSTRACT
A particular strength of lightning remote sensing is the variety of lightning types observed, each with a unique occurrence context and characteristically different emission. Distinct energetic intracloud (EIC) lightning discharges-compact intracloud lightning discharges (CIDs) and energetic intracloud pulses (EIPs)-produce intense RF radiation, suggesting large currents inside the cloud, and they also have different production mechanisms and occurrence contexts. A Low-Frequency (LF) lightning remote sensing instrument array was deployed during the RELAMPAGO field campaign in west central Argentina, designed to investigate convective storms that produce high-impact weather. LF data from the campaign can provide a valuable data set for researching the lightning context of EICs in a variety of subtropical convective storms. This paper describes the production of an LF-CID data set in RELAMPAGO and includes a preliminary analysis of CID prevalence. Geolocated lightning events and their corresponding observed waveforms from the RELAMPAGO LF data set are used in the classification of EICs. Height estimates based on skywave reflections are computed, where prefit residual data editing is used to improve robustness against outliers. Even if EIPs occurred within the network, given the low number of very high-peak current events and receiver saturation, automatic classification of EIPs may not be feasible using this data. The classification of CIDs, on the other hand, is straightforward and their properties, for both positive and negative polarity, are investigated. A few RELAMPAGO case studies are also presented, where high variability of CID prevalence in ordinary storms and high-altitude positive CIDs, possibly in overshooting tops, are observed.
ABSTRACT
The lightning data products generated by the low-frequency (LF) radio lightning locating system (LLS) deployed during the Remote sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observation (RELAMPAGO) field campaign in Argentina provide a valuable data set to research the lightning evolution and characteristics of convective storms that produce high-impact weather. LF LLS data sets offer a practical range for mesoscale studies, allowing for the observation of lightning characteristics of storms such as mesoscale convective systems 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 cloud-to-ground flash rate) or narrow bipolar events which may often be associated with dynamically intense convection. In this article, the geolocation and data processing of the LF data set collected during RELAMPAGO is fully described and its performance characterized, with location accuracy better than 10 km. The detection efficiency (DE) of the data set is compared to that of the Geostationary Lightning Mapper, and spatiotemporal DE losses in the LF data set are discussed. Storm case studies on November 10, 2018, highlight the strengths of the data set, which include robust flash clustering and insightful flash rate and peak current measures, while illustrating how its limitations, including DE losses, can be managed.
ABSTRACT
The atmospheric electric field is an important research parameter in understanding storm electrification and energy exchange between lightning and the atmosphere across the globe. The near-surface electric field can range from a few V/m (order of 10-100 V/m), mainly produced by the currents in the global electric circuit and local charge perturbations, to tens of kV/m in the presence of electrified clouds. The electric field mill (EFM), a variable capacitance electrometer, has been the instrument of choice in the atmospheric electricity community studying phenomena associated with the atmospheric electric field. The EFM is particularly useful in following storm movement and evolution, monitoring the fair-weather electric field at distant locations, and measuring the vertical electric field inside clouds with EFM deployments on balloons. In this paper, we describe a new electric field mill ground-based design, which focuses on lowering the manufacturing and operational costs of doing research with an array of EFM instruments while maintaining the scientific capabilities offered by past designs and commercially available devices. The theory of operation, data processing, and calibration of the instrument are also described. Example data from the first generation of these new field mills, deployed in the RELAMPAGO campaign in Argentina, are presented here. The RELAMPAGO deployment and data set illustrate important strengths of this design, for example, cost, autonomy, longevity, and measurement quality.
