Michael Stock

Balloon-borne electric field meters have been used to study the electrical environment of thunderstorms since the 1970s; even so, descriptions of how they function are incomplete. This study serves as a consolidated and comprehensive reference to how these instruments work, including physical and electrical descriptions of the instrument and details about how they are launched into thunderstorms. The mathematical method used to convert the modulated voltage signal recorded by the electric field meter into a three-dimensional measurement of the electric field is also provided here for the first time. The study also expands on these methods by examining how a swinging instrument package can affect the measured signals and the demodulated electric field. Balloon-borne electric field measurements are frequently used to estimate the charge density in thunderstorms using a one-dimensional Gauss approximation. An analysis of simulated balloon flights through simulated storms is used to evaluate how representative this approximation is. In general, charge retrievals were representative but underestimated the charge density at the balloon package. Better agreement was found with a horizontal average of the thundercloud charge density, but the estimation was still prone to errors in the vicinity of some lightning flashes. Significance Statement: This study serves as a consolidated and comprehensive reference on how balloon-borne electric field meters function. This includes a physical and electrical description of the instrument, details of how the instrument is launched into thunderstorms, and the mathematical methods required to convert the recorded signals into measurements of electric field. In addition, the effects of a swinging instrument were investigated, and methods to identify swing in the recorded data are documented. Finally, a simulation was performed to test the ability of balloon-borne electric field meters to estimate the charge density in realistic thunderstorm environments.

The Long Wavelength Array is a radio telescope array located at the Sevilleta National Wildlife Refuge in La Joya, New Mexico, well suited and situated for the observation of lightning. The array consists of 256 high-sensitivity dual polarization antennas arranged in a 100 m diameter. This paper demonstrates some of the capabilities that the array brings to the study of lightning. Once 32 or more antennas are used to image lightning radio sources, virtually every integration period longer than the impulse response of the array includes at least one identifiable lightning emitter, independent of the integration period used. The use of many antennas also allows multiple simultaneous lightning radio sources to be imaged at sub-microsecond timescales; for the flash examined, 51% of the images contained more than one lightning source. Finally, by using many antennas to image lightning sources, the array is capable of locating sources fainter than the galactic background radio noise level, yielding possibly the most sensitive radio maps of lightning to date. This incredible sensitivity enables, for the first time, the emissions originating from the positive leader tips of natural in-cloud lightning to be detected and located. The tip emission is distinctly different from needle emission and is most likely due to positive breakdown.

The Earth Networks Total Lightning Network (ENTLN) launched a new processor (P2021) in December 2021. Some major upgrades were made in the new processor, including a new classification algorithm, a new propagation model, and regional data processing architecture. Ground-truth datasets of natural and rocket-triggered lightning acquired in Florida were used to evaluate the performance characteristics of the new processor. Compared to the last processor launched in 2015 (P2015), the stroke classification accuracy increased from 91% to 94% for natural lightning and from 86% to 88% for rocket-triggered lightning. The location accuracy improved significantly with the median location error decreasing from 215 m to 92 m. On a global scale, we found the number of pulses detected by the ENLTN increased in all regions with an overall detection gain of 149%. One can see modest gains in detection in regions with a fairly dense network of sensors and significant gains in regions where sensor density is much lower. Each of the major upgrades as well as their influences on the performance characteristics of the ENLTN are discussed.

The 2019–2020 Australian wildfire crisis broke the historical bushfire record and heavily contaminated the continental and offshore atmosphere. This study found that lightning strokes increase considerably, by 73% over land and 270% over ocean, during the wildfire season. Thermodynamic parameters support a weaker forcing, unfavorable for frequent lightning activity over ocean. Clear augmentation of smaller cloud ice particles is identified with aerosol, while cloud liquid water path changes are feeble over ocean. Added aerosol invigorates positive intra‐cloud (IC) strokes and negative cloud‐to‐ground (CG) strokes in moist oceanic convection and facilitates a noticeable positive correlation between precipitation and lightning strokes. Rainfall events accompanied by lightning increase by 240% with added aerosol. Aerosol advected from land to ocean can lead to a larger hydrometeor concentration and smaller‐size ice crystals above the freezing level and thereby, invigorate convective strength systematically to stimulate more frequent and more robust mixed‐phase development, energizing the lightning discharge process.

Many studies have shown that the characteristics of lightning such as size and peak current differ between ocean and continental thunderstorms. In general, the lightning in oceanic thunderstorms are larger and have higher peak current than in continental thunderstorms. The reason for these differences have been stipulated to be related to differences in thermal properties and aerosol concentration, however, there is still disagreement over which is the dominant mechanism. In this study, we focus on how thunderstorm trends, as opposed to lightning trends (i.e., flash density), are affected by these mechanisms. We develop a lightning clustering algorithm that takes individual lightning strokes and creates thunderstorms based on their spatiotemporal proximity. We use lightning data from the Earth Networks Total Lightning Network and compare storms from the Eastern U.S.A. to storms off that coast, where the detection efficiency of the network is still good. Once these thunderstorms are obtained, we can split them into ocean and land thunderstorms and compare various characteristics (size, duration, flash rate, polarity and IC/CG ratio, etc.) to determine if any differences stand out. In this presentation, we will discuss the clustering algorithm used, analyze the results of the study, and discuss implications.