A5058882814- Lightning and Electromagnetic Phenomena
- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Astro and Planetary Science
- Electrostatic Discharge in Electronics
- High voltage insulation and dielectric phenomena
- Astrophysics and Cosmic Phenomena
- Earthquake Detection and Analysis
- Fire effects on ecosystems
- Gamma-ray bursts and supernovae
- Electromagnetic Compatibility and Noise Suppression
- Electrical Fault Detection and Protection
- Advanced Optical Sensing Technologies
- Power Line Communications and Noise
- Stellar, planetary, and galactic studies
- Particle Detector Development and Performance
- Aerosol Filtration and Electrostatic Precipitation
- Dark Matter and Cosmic Phenomena
- Nuclear Physics and Applications
- Atmospheric aerosols and clouds
- Atomic and Subatomic Physics Research
- Geophysics and Gravity Measurements
- Radio Astronomy Observations and Technology
- Radiation Detection and Scintillator Technologies
- Radio Wave Propagation Studies
University of New Hampshire
2016-2025
University of New Hampshire at Manchester
2014-2023
Vrije Universiteit Brussel
2023
University of Naples Federico II
2023
University of Massachusetts Amherst
2019-2021
Florida Institute of Technology
2006-2015
Institute of Molecular Biology and Biophysics
2010
University of Maryland, College Park
1997-2001
Columbia University
1994-1998
University of Chicago
1992
It is now well established that both thunderclouds and lightning routinely emit x-rays gamma-rays. These emissions appear over wide timescales, ranging from sub-microsecond bursts of associated with leaders, to sub-millisecond gamma-rays seen in space called terrestrial gamma-ray flashes, minute long glows on the ground or near cloud by aircraft balloons. In particular, flashes (TGFs), which are thought be emitted thunderclouds, so bright they sometimes saturate detectors spacecraft hundreds...
The Gamma‐ray Burst Monitor (GBM) on the Fermi Space Telescope detected 12 intense terrestrial gamma ray flashes (TGFs) during its first year of observation. Typical maximum energies for most TGFs are ∼30 MeV, with one TGF having a 38 MeV photon; two softer and longer than others. After correcting instrumental effects, representative bright is found to have fluence ∼0.7 photons cm −2 . Pulses either symmetrical or faster risetimes fall times; they well fit Gaussian lognormal functions....
By modifying the avalanche mode of runaway breakdown to include positive feedback from gamma‐rays and positrons, it is found that enormous bursts energetic radiation can be produced in strong electric fields air, with peak fluxes up one billion times greater than conventional models. These generate so many electrons field very rapidly discharged, resulting a fundamental upper limit on strength achievable air. This has important implications for electrification thunderstorms production lightning.
Monte Carlo simulations of the runaway breakdown air are used to calculate spectra terrestrial gamma‐ray flashes (TGFs), which then compared with RHESSI and CGRO/BATSE observations. It is found that recent spectrum not consistent a source altitude above 24 km but can be well fit by in range 15–21 km, depending upon electric field geometry source. Because 15 unusual for tops thunderstorms, especially at low latitudes, lower than typical minimum sprite altitudes, data imply thunderstorms...
We have studied fine-scale temporal variations in the arrival profiles of approximately 20 keV nucleon-1 to 2 MeV ions from impulsive solar flares using instrumentation on board Advanced Composition Explorer spacecraft at 1 AU between 1997 November and 1999 July. The particle events often had short-timescale ( 3 hr) their intensity that occurred simultaneously across all energies were generally not coincidence with any local magnetic field or plasma signature. These features appear be caused...
We have measured the 3He abundance from approximately 0.5 to 2 MeV nucleon-1 in 12 large solar energetic particle (SEP) events during period 1997 November-1999 June. In five of events, time-intensity profile is similar 4He profile, indicating a common acceleration and transport origin for two species. The average 3He/4He ratio these &parl0;1.9+/-0.2&parr0;x10-3, factor 5 enhancement over wind value. During this same survey period, we also low-energy ion intensities quieter periods between...
X‐ray and electric field measurements were made during five nearby negative natural lightning strikes in north central Florida the summer of 2004. The observed emission typically was detected ∼1 ms before first return stroke, stepped‐leader phase, had energies extending up to a few hundred keV. X rays produced discrete, intense bursts emitted coincidence with formation leader steps, demonstrating unambiguously that source is closely related stepping process. from stepped leaders found be...
We have surveyed the 0.1-10 MeV nucleon-1 elemental abundances at 72 interplanetary (IP) shocks observed by Ultra-Low-Energy Isotope Spectrometer on board Advanced Composition Explorer from 1997 October through 2002 September. find following: (1) The C/O ratios in IP were substantially depleted (by more than ~40%) relative to solar wind values. (2) shock poorly correlated with those measured slow and fast wind. (3) Energetic ions above ~0.1 impulsive gradual energetic particle events (SEPs)...
The source of terrestrial gamma‐ray flashes (TGFs) has remained a mystery since their discovery in 1994. Recent Reuven Ramaty High‐Energy Solar Spectroscopic Imager (RHESSI) observations show that these intense bursts MeV gamma rays likely originate much deeper the atmosphere than previously inferred from Burst and Transient Source Experiment (BATSE) data, with altitude <21 km. Using existing measurements intensity duration BATSE RHESSI TGFs, along limits on electric field set by...
As thunderclouds charge, the large‐scale fields may approach relativistic feedback threshold, above which production of runaway electron avalanches becomes self‐sustaining through generation backward propagating positrons and backscattered X‐rays. Positive intracloud (IC) lightning force electric inside causing number electrons, resulting X‐ray gamma ray emission, to grow exponentially, producing very large fluxes energetic radiation. flux electrons increases, ionization eventually causes...
In 2003, a new electrical breakdown mechanism involving the production of runaway avalanches by positive feedback from positrons and energetic photons was introduced. This mechanism, which shall be referred to as “relativistic feedback,” allows discharges in gases become self-sustaining, dramatically increasing flux electrons, accompanying high-energy radiation, resulting ionization. Using detailed Monte Carlo calculations, properties relativistic are investigated. It is found that once...
Abstract Radio emissions continue to provide insight into the production of terrestrial gamma ray flashes (TGFs) by thunderstorms, including critical question conditions under which they are generated. We have identified several TGF‐associated lightning radio in altitudes in‐cloud leader pulses that precede and follow TGF can be measured. combine these with high absolute timing accuracy observations from Fermi satellite determine development channel before, during, after production. All TGFs...
Abstract Thunderstorms are natural laboratories for studying electrical discharges in air, where the vast temporal, spatial, and energy scales available can spawn surprising phenomena that reveal deficiencies our understanding of dielectric breakdown. Recent discoveries, such as sprites, jets, terrestrial gamma ray flashes, fast positive breakdown, highlight diversity complex thunderstorms produce, point to possibility breakdown/discharge mechanisms beyond breakdown theory based mainly on...
Abstract We report on a terrestrial gamma ray flash (TGF) that occurred 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 ground‐level network of ray, close electric field, distant magnetic Mapping Array (LMA), optical, radar measurements. Simultaneous LMA data indicate upward positive leader triggered induced relativistic runaway electron avalanches when tip...
Abstract In this work, detailed Monte Carlo simulations were performed to test whether terrestrial gamma‐ray flashes (TGFs) may be produced by thunderstorm electrification alone, without the presence of lightning, relativistic feedback mechanism. TGFs are powerful bursts gamma rays thunderstorms, often in association with lightning. They bremsstrahlung interactions runaway electrons air, typically requiring >10 17 energetic account for emissions. These high‐field regions near lightning...
Using a NaI(Tl) scintillation detector designed to operate in electrically noisy environments, we observed intense bursts of energetic radiation (>> 10 kiloelectron volts) during the dart leader phase rocket-triggered lightning, just before and possibly at very start 31 out 37 return strokes measured. The had typical durations less than 100 microseconds deposited many tens megaelectron volts into detector. These results provide strong evidence that production runaway electrons is an...
We have surveyed 3He-rich solar energetic particle (SEP) events over the period 1997 September-2003 April in order to characterize abundances of heavy ions near 400 keV nucleon-1. The first part study focuses on 20 distinct SEP that show previously observed pattern which, relative O, through Fe are enriched, with enrichment increasing mass. find these enrichments well correlated such high Fe/C also larger other ions. Ultraheavy (UH; taken as 78-220 amu) routinely seen abundance enhancements...
We report the observation of an intense gamma‐ray burst observed on ground at sea level, produced in association with initial‐stage rocket‐triggered lightning International Center for Lightning Research and Testing Camp Blanding, FL. The was simultaneously three NaI(Tl)/photomultiplier tube detectors that were located 650 m from triggered channel energies extending up to more than 10 MeV. consisted 227 individual gamma‐rays arrived over a 300 μs time period coincidence 11 kA current pulse....
We have surveyed the $0.1-10MeV nucleon À1 abundances of heavy ions from 3 He through Fe in 64 large solar energetic particle (LSEP) events observed on board Advanced Composition Explorer 1997 November 2005 January.Our main results are (1) 0.5-2.0MeV He/ 4 ratio is enhanced between factors $2-150 over wind value 29 ($46%) events.(2) The Fe/O most LSEP decreases with increasing energy up to $60 MeV .(3) independent CME speed, flare longitude, event size, ratio, pre-event and activity.(4)...
Using CGRO/BATSE data, a possible new source of high‐energy electrons and positrons in the earth's inner magnetosphere is presented. These particles are generated within upper atmosphere by Compton scattering pair‐production gamma‐rays originating from near tropopause as Terrestrial Gamma‐ray Flashes (TGFs). Once created, these energetic follow geomagnetic field into where they can be detected low‐earth orbit, either TGF magnetic foot point or at conjugate several thousand kilometers away....
[1] We analyze the count rates of two terrestrial gamma‐ray flashes (TGFs) detected by Fermi Gamma‐ray Burst Monitor (GBM) with broadband magnetic fields (1 to 300 kHz) produced simultaneous lightning processes. The microsecond‐scale absolute time accuracy for these data, combined independent geolocations source lightning, enable this analysis higher than previously possible. In both events, fast discharge‐like processes occur within several tens microseconds generation, although not a...
We present 10 high‐speed video images that depict the bottom 150 m of a downward‐negative, dart‐stepped leader in rocket‐and‐wire triggered flash, recorded at 240 kiloframes per second (4.17 μ s frame integration time), along with correlated measurements X‐ray emission 50 m, electric field derivative (dE/dt) 80 and rocket‐launch‐tower current beneath leader. observed discrete segments secondary channel exhibited luminosity above surrounding corona streamers were distinctly separate...