B. M. Hare

Rocket‐triggered lightning propagation paths relative to preceding natural lightning activity and inferred cloud charge

Lightning Mapping Array (LMA) data are used to compare the propagation paths of seven rocket-triggered lightning flashes to the inferred charge structure of the thunderstorms in which they were triggered. This is the first LMA study of Florida thunderstorm charge structure. Three sequentially (within 16u2009min) triggered lightning flashes, whose initial stages were the subject of Hill et al. (2013), are reexamined by comparing the complete flashes to the preceding natural lightning to demonstrate that the three rocket-triggered flashes propagated through an inferred negative charge region that decreased from about 6.8 to about 4.4u2009km altitude as the thunderstorm dissipated. Two other flashes were also sequentially triggered (within 9u2009min) in a thunderstorm that contained a convectively intense region ahead of a stratiform region, with similar observed results. Finally, two unique cases of triggered lightning flashes are presented. In the first case, the in-cloud portion of the triggered lightning flash, after ascending to and turning horizontal at 5.3u2009km altitude, just above the 0°C level, was observed to very clearly resemble the geometry of the in-cloud portion of the preceding natural lightning discharges. In the second case, a flash was triggered relatively early in the storms lifecycle that did not turn horizontal near the 0°C level, as is usually the case for triggered lightning in dissipating storms, but ascended to nearly 7.5u2009km altitude before exhibiting extensive horizontal branching.

Ground‐level Observation of a Terrestrial Gamma Ray Flash Initiated by a Triggered Lightning

We report on a terrestrial gamma ray flash (TGF) that occurred on 15 August 2014 coincident with an altitude-triggered lightning at the International Center for Lightning Research and Testing (ICLRT) in North Central Florida. The TGF was observed by a ground-level network of gamma ray, close electric field, distant magnetic field, Lightning Mapping Array (LMA), optical, and radar measurements. Simultaneous gamma ray and LMA data indicate that the upward positive leader of the triggered lightning flash induced relativistic runaway electron avalanches when the leader tip was at about 3.5xa0km altitude, resulting in the observed TGF. Channel luminosity and electric field data show that there was an initial continuous current (ICC) pulse in the lightning channel to ground during the time of the TGF. Modeling of the observed ICC pulse electric fields measured at close range (100–200xa0m) indicates that the ICC pulse current had both a slow and fast component (full widths at half maximum of 235xa0μs and 59xa0μs) and that the fast component was more or less coincident with the TGF, suggesting a physical association between the relativistic runaway electron avalanches and the ICC pulse observed at ground. Our ICC pulse model reproduces moderately well the measured close electric fields at the ICLRT as well as three independent magnetic field measurements made about 250xa0km away. Radar and LMA data suggest that there was negative charge near the region in which the TGF was initiated.

Initial breakdown and fast leaders in lightning discharges producing long lasting disturbances of the lower ionosphere

The recent discovery of long recovery, early VLF scattering events (LOREs) indicates that the electric field changes from lightning discharges are capable of producing long-lasting disturbances (up to tens of minutes) in the upper mesosphere and lower ionosphere. Comparison of lightning mapping array, broadband (up to 10xa0MHz) electric field, and VLF (∼300xa0Hz to 42xa0kHz) magnetic field measurements shows that the field changes produced by initial breakdown (IB) processes and the following leaders in natural, cloud-to-ground lightning discharges are detectable in VLF magnetic field measurements at long distances. IB radiation has been detected in VLF for lightning discharges occurring up to 2630xa0km away from the VLF observing station. Radio atmospherics associated with 52 LOREs, 51 regular recovery events, and 3098 flashes detected by National Lightning Detection Network and/or GLD360 were examined for IB radiation occurring up to 15xa0ms before the return stroke. Our analysis reveals that in contrast to regular recovery early VLF events, LOREs are strongly associated with lightning discharges which exhibit an intense IB process and a fast first leader (typical duration <4xa0ms). These experimental results demonstrate that initial breakdown and leader processes are indicators of discharge properties highly relevant to the total energy transfer between lightning discharges and the middle/upper atmosphere.

Thunderstorm electric fields probed by extensive air showers through their polarized radio emission

We observe a large fraction of circular polarization in radio emission from extensive air showers recorded during thunderstorms, much higher than in the emission from air showers measured during fair-weather circumstances. We show that the circular polarization of the air showers measured during thunderstorms can be explained by the change in the direction of the transverse current as a function of altitude induced by atmospheric electric fields. Thus by using the full set of Stokes parameters for these events, we obtain a good characterization of the electric fields in thunderclouds. We also measure a large horizontal component of the electric fields in the two events that we have analyzed.

Characterisation of the radio frequency spectrum emitted by high energy air showers with LOFAR

The high number density of radio antennas at the LOFAR core in Northern Netherlands allows to detect radio signals emitted by extensive air showers in the energy range 10

Evaluation of ENTLN Performance Characteristics Based on the Ground Truth Natural and Rocket‐Triggered Lightning Data Acquired in Florida

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Do cosmic ray air showers initiate lightning? : A statistical analysis of cosmic ray air showers and lightning mapping array data

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Analytic calculation of radio emission from parametrized extensive air showers : A tool to extract shower parameters

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LOFAR Lightning Imaging : Mapping Lightning With Nanosecond Precision

eV, and to characterise the geometry of the observed cascade in a detailed way. The radio signal emitted by extensive air showers along their propagation in the atmosphere has been studied in the 30 − 70 MHz frequency range. The study has been conducted on real data and simulated showers. Regarding real data, cosmic ray radio signals detected by LOFAR since 2011 have been analysed. For simulated showers, the CoREAS code, a plug-in of the CORSIKA particle simulation code, has been used. The results show a clear dependence of the frequency spectrum on the distance to the shower axis for both real data and simulations. In particular, the spectrum flatten at a distance around 100 m from the shower axis, where the coherence of the radio signal is maximum. This behaviour could also be used to reconstruct the position of the shower axis at ground. A correlation between the frequency spectrum and the geometrical distance to the depth of the shower maximum X

Overview and Status of the Lunar Detection of Cosmic Particles with LOFAR

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