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Full-Text Articles in Physical Sciences and Mathematics
High-Altitude Electrical Discharges Associated With Thunderstorms And Lightning, Ningyu Liu, Matthew G. Mcharg, Hans C. Stenbaek-Nielsen
High-Altitude Electrical Discharges Associated With Thunderstorms And Lightning, Ningyu Liu, Matthew G. Mcharg, Hans C. Stenbaek-Nielsen
Aerospace, Physics, and Space Science Faculty Publications
The purpose of this paper is to introduce electrical discharge phenomena known as transient luminous events above thunderstorms to the lightning protection community. Transient luminous events include the upward electrical discharges from thunderstorms known as starters, jets, and gigantic jets, and electrical discharges initiated in the lower ionosphere such as sprites, halos, and elves. We give an overview of these phenomena with a focus on starters, jets, gigantic jets, and sprites, because similar to ordinary lightning, streamers and leaders are basic components of these four types of transient luminous events. We present a few recent observations to illustrate their main …
Modeling Terrestrial Gamma Ray Flashes Produced By Relativistic Feedback Discharges, Ningyu Liu, Joseph R. Dwyer
Modeling Terrestrial Gamma Ray Flashes Produced By Relativistic Feedback Discharges, Ningyu Liu, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
This paper reports a modeling study of terrestrial gamma ray flashes (TGFs) produced by relativistic feedback discharges. Terrestrial gamma ray flashes are intense energetic radiation originating from the Earth’s atmosphere that has been observed by spacecraft. They are produced by bremsstrahlung interactions of energetic electrons, known as runaway electrons, with air atoms. An efficient physical mechanism for producing large fluxes of the runaway electrons to make the TGFs is the relativistic feedback discharge, where seed runaway electrons are generated by positrons and X-rays, products of the discharge itself. Once the relativistic feedback discharge becomes self-sustaining, an exponentially increasing number of …
The Angular Distribution Of Energetic Electron And X-Ray Emissions From Triggered Lightning Leaders, M. M. Schaal, Joseph R. Dwyer, Hamid K. Rassoul, Jonathan David Hill, Douglas M. Jordan, Martin A. Uman
The Angular Distribution Of Energetic Electron And X-Ray Emissions From Triggered Lightning Leaders, M. M. Schaal, Joseph R. Dwyer, Hamid K. Rassoul, Jonathan David Hill, Douglas M. Jordan, Martin A. Uman
Aerospace, Physics, and Space Science Faculty Publications
We investigate individual X-ray bursts from lightning leaders to determine if energetic electrons at the source (and hence X-rays) are emitted isotropically or with some degree of anisotropy. This study was motivated by the work of Saleh et al. (2009), which found the falloff of X-rays in concentric radial annuli, covering all azimuthal directions in each annulus, from the lightning channel to be most consistent with an isotropic electron source. Here we perform a statistical analysis of angular and spatial distributions of X-rays measured by up to 21 NaI/PMT detectors at the International Center for Lightning Research and Testing site …
Radio Emissions From Terrestrial Gamma-Ray Flashes, Joseph R. Dwyer, Steven A. Cummer
Radio Emissions From Terrestrial Gamma-Ray Flashes, Joseph R. Dwyer, Steven A. Cummer
Aerospace, Physics, and Space Science Faculty Publications
The theory of radio frequency (RF) emissions by terrestrial gamma-ray flashes (TGFs) is developed. These radio emissions, which are separate from the emission caused by lightning, are produced by the electric currents generated by runaway electrons and resulting low-energy electrons and ions. It is found from theory that the radio frequency pulses produced by TGFs are large enough to measure. Features of these signals depend strongly on certain aspects of the runaway acceleration process and so should provide additional information about the source mechanism(s) of this interesting atmospheric phenomenon. The RF emissions from several TGF models are calculated and compared …
Radio Signals From Electron Beams In Terrestrial Gamma Ray Flashes, Valerie Connaughton, Joseph R. Dwyer, Eric Cramer
Radio Signals From Electron Beams In Terrestrial Gamma Ray Flashes, Valerie Connaughton, Joseph R. Dwyer, Eric Cramer
Aerospace, Physics, and Space Science Faculty Publications
We show that the rate of association between terrestrial gamma ray flashes (TGFs) observed by the Fermi gamma ray burst monitor and VLF discharges detected by the World Wide Lightning Location Network (WWLLN) depends strongly on the duration of the TGF, with the shortest TGFs having associated WWLLN events over 50% of the time, and the longest TGFs showing a less than 10% match rate. This correlation is stronger if one excludes the WWLLN discharges that are not simultaneous (within 200 ms) with the TGF. We infer that the simultaneous VLF discharges are from the relativistic electron avalanches that are …
Analysis Of The Experiment On Registration Of X-Rays From The Stepped Leader Of A Cloud-To-Ground Lightning Discharge, Leonid P. Babich, Igor M. Kutsyk, Evgeni N. Donsko, Joseph R. Dwyer
Analysis Of The Experiment On Registration Of X-Rays From The Stepped Leader Of A Cloud-To-Ground Lightning Discharge, Leonid P. Babich, Igor M. Kutsyk, Evgeni N. Donsko, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
Using a Monte Carlo technique to simulate the transport of runaway electrons (REs) and X-rays in the atmosphere and through attenuators covering detectors, we have modeled the results of experiments to detect X-rays from triggered lightning and stepped leaders of a natural cloud-to-ground lightning. In the model, bremsstrahlung of high-energy runaway electrons (REs) generated at the leader front is assumed to be the origin of X-rays. Specific fluxes (per one RE) of photons and bremsstrahlung energy at the detectors were calculated. The analysis was executed with monoenergetic and exponential initial energy distributions of REs with different angular distributions. To reproduce …
A Terrestrial Gamma Ray Flash Observed From An Aircraft, D. M. Smith, Michael E. Splitt, Steven M. Lazarus
A Terrestrial Gamma Ray Flash Observed From An Aircraft, D. M. Smith, Michael E. Splitt, Steven M. Lazarus
Aerospace, Physics, and Space Science Faculty Publications
On 21 August 2009, the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of six gamma-ray detectors, detected a brief burst of gamma rays while flying aboard a Gulfstream V jet near two active thunderstorm cells. The duration and spectral characteristics of the event are consistent with the terrestrial gamma ray flashes (TGFs) seen by instruments in low Earth orbit. A long-duration, complex +IC flash was taking place in the nearer cell at the same time, at a distance of ∼10 km from the plane. The sferics that are probably associated with this flash extended over 54 ms and …
The Lightning-Tgf Relationship On Microsecond Ttimescales, Steven A. Cummer, Gaopeng Lu, Michael S. Briggs, Valerie Connaughton, Shaolin Xiong, Gerald Jerry Fishman, Joseph R. Dwyer
The Lightning-Tgf Relationship On Microsecond Ttimescales, Steven A. Cummer, Gaopeng Lu, Michael S. Briggs, Valerie Connaughton, Shaolin Xiong, Gerald Jerry Fishman, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
We analyze the count rates of two terrestrial gamma-ray flashes (TGFs) detected by the Fermi Gamma-ray Burst Monitor (GBM) with the broadband magnetic fields (1 to 300 kHz) produced by the simultaneous lightning processes. The microsecond-scale absolute time accuracy for these data, combined with independent geolocations of the source lightning, enable this analysis with higher accuracy than previously possible. In both events, fast discharge-like processes occur within several tens of microseconds of the gamma-ray generation, although not with a consistent relationship. The magnetic field data also show a slower signal component produced by a source current that in both events …
High-Speed X-Ray Images Of Triggered Lightning Dart Leaders, Joseph R. Dwyer, M. M. Schaal, Hamid K. Rassoul, Martin A. Uman, Douglas M. Jordan, Dustin Hill
High-Speed X-Ray Images Of Triggered Lightning Dart Leaders, Joseph R. Dwyer, M. M. Schaal, Hamid K. Rassoul, Martin A. Uman, Douglas M. Jordan, Dustin Hill
Aerospace, Physics, and Space Science Faculty Publications
We present the first high-time resolution two-dimensional images of X-ray emissions from lightning. The images were recorded at a rate of 10 million per second using a new pinhole-type camera, located 44 m from rocket-and-wire- triggered lightning. We report observations of two dart leaders, one in each of two lightning flashes triggered during the summer of 2010 in north-central Florida. In both events, as the dart leader approached the ground, the X-ray source was also seen to descend along the previous lightning channel. For the second event, the X-ray source exhibited a downward speed of 4.5 × 10 7 m/s, …
Model Of Sprite Luminous Trail Caused By Increasing Streamer Current, Ningyu Liu
Model Of Sprite Luminous Trail Caused By Increasing Streamer Current, Ningyu Liu
Aerospace, Physics, and Space Science Faculty Publications
This study investigates a possible physical mechanism responsible for the occurrence of the luminous trail of sprite streamers, which is also known as "afterglow." According to streamer modeling results, when sprite streamers propagate with expansion, acceleration and brightening, the total current flowing through the streamer body also increases. The increasing current results in the rise of the electric field in the streamer channel far behind the streamer head, which leads to effective production of N₂ excited states by electron impact excitation and then the glowing trail.
Spectral Dependence Of Terrestrial Gamma-Ray Flashes On Source Distance, Bryna J. Hazelton, Brian W. Grefenstette, David M. Smith, Joseph R. Dwyer, Xuanmin Shao, Steven A. Cummer, Themis G. Chronis, Erin H. Lay, Robert H. Holzworth
Spectral Dependence Of Terrestrial Gamma-Ray Flashes On Source Distance, Bryna J. Hazelton, Brian W. Grefenstette, David M. Smith, Joseph R. Dwyer, Xuanmin Shao, Steven A. Cummer, Themis G. Chronis, Erin H. Lay, Robert H. Holzworth
Aerospace, Physics, and Space Science Faculty Publications
We use lightning sferics from the World Wide Lightning Location Network to identify storms near 362 Terrestrial Gamma-ray Flashes (TGFs). The combined spectrum of TGFs with storms within 300 km of the sub-satellite point is much harder than the spectrum of TGFs with more distant storms. When these data are compared with simulations of vertically oriented relativistic runaway breakdown, it is found that the most likely model has a source altitude of 15 km and a wide-beam geometry. We find four associations of TGFs with individual sferics geolocated to positions more than 300 km from the sub-satellite point and show …
High-Energy Electron Beams Launched Into Space By Thunderstorms, Joseph R. Dwyer, Brian W. Grefenstette, David M. Smith
High-Energy Electron Beams Launched Into Space By Thunderstorms, Joseph R. Dwyer, Brian W. Grefenstette, David M. Smith
Aerospace, Physics, and Space Science Faculty Publications
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 the upper atmosphere by Compton scattering and pair-production of gamma-rays originating from near the tropopause as Terrestrial Gamma-ray Flashes (TGFs). Once created, these energetic electrons and positrons follow the geomagnetic field into the inner magnetosphere where they can be detected in low-earth orbit, either near the TGF magnetic foot point or at the conjugate point several thousand kilometers away. Approximately 17% of CGRO/BATSE events previously identified as terrestrial gamma-ray flashes are, in fact, such electrons and …
Co-Location Of Lightning Leader X-Ray And Electric Field Change Sources, John J. Howard, Martin A. Uman, Joseph R. Dwyer, Dustin Hill, Christopher J. Biagi, Ziad H. Saleh, Jason E. Jerauld, Hamid K. Rassoul
Co-Location Of Lightning Leader X-Ray And Electric Field Change Sources, John J. Howard, Martin A. Uman, Joseph R. Dwyer, Dustin Hill, Christopher J. Biagi, Ziad H. Saleh, Jason E. Jerauld, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
Using an eight-station time of arrival (TOA) network composed of NaI(Tl) scintillation detectors and wideband electric field derivative (dE/dt) antennas covering approximately 1 km² on the ground, we have located both the sources of X-ray emissions and electric field changes produced during the leader phase of both downward negative natural and rocket-triggered lightning strokes. We show that the sources of X rays and leader step electric field changes are co-located in space within 50 m and that the located X rays are emitted 0.1 to 1.3 μs after the origin of the leader step electric field changes.
Time Evolution Of Terrestrial Gamma Ray Flashes, Brian W. Grefenstette, David M. Smith, Joseph R. Dwyer, Gerald Jerry Fishman
Time Evolution Of Terrestrial Gamma Ray Flashes, Brian W. Grefenstette, David M. Smith, Joseph R. Dwyer, Gerald Jerry Fishman
Aerospace, Physics, and Space Science Faculty Publications
We present a study of the time evolution of TGFs observed by both RHESSI and BATSE and compare the data with Monte Carlo simulations of relativistic runaway electron avalanches that record the time of flight for individual photons. Our analysis of the RHESSI data shows that the average delay between the main, hard peak and the secondary, soft tail in the RHESSI data is 28 ± 3 μs. We show that this is consistent with Compton downscattering of hard photons in the atmosphere in our simulations when the source region is located at or below 21 km, which is consistent …
Correlation Between Energetic Ion Enhancements And Heliospheric Current Sheet Crossings In The Outer Heliosphere, John D. Richardson, Edward C. Stone, Ace C. Cummings, Justin C. Kasper, Ming Zhang, Leonard F. Burlaga, Nudel F. Ness, Ying Liu
Correlation Between Energetic Ion Enhancements And Heliospheric Current Sheet Crossings In The Outer Heliosphere, John D. Richardson, Edward C. Stone, Ace C. Cummings, Justin C. Kasper, Ming Zhang, Leonard F. Burlaga, Nudel F. Ness, Ying Liu
Aerospace, Physics, and Space Science Faculty Publications
Voyagers 1 and 2 observed highly-variable beams of energetic ions in the foreshock region upstream of the termination shock (TS). At Voyager 2 (V2), the ion intensities are generally not related to the plasma properties. At Voyager 1 (V1), the beams are often coincident with crossings of the heliospheric current sheet (HCS). The V1 intensity peaks occur when the HCS is crossed from negative to positive magnetic polarities and V1 is within a few AU of the TS. Two mechanisms are considered: current sheet drift and streaming of ions from the TS along magnetic field lines which are parallel to …
A Comparison Between Monte Carlo Simulations Of Runaway Breakdown And Terrestrial Gamma-Ray Flash Observations, Joseph R. Dwyer, David M. Smith
A Comparison Between Monte Carlo Simulations Of Runaway Breakdown And Terrestrial Gamma-Ray Flash Observations, Joseph R. Dwyer, David M. Smith
Aerospace, Physics, and Space Science Faculty Publications
Monte Carlo simulations of the runaway breakdown of air are used to calculate the spectra of terrestrial gamma-ray flashes (TGFs), which are then compared with RHESSI and CGRO/BATSE observations. It is found that the recent RHESSI spectrum is not consistent with a source altitude above 24 km but can be well fit by a source in the range of 15-21 km, depending upon the electric field geometry of the source. Because 15 km is not unusual for the tops of thunderstorms, especially at low latitudes, and is lower than typical minimum sprite altitudes, the RHESSI data imply that thunderstorms and …
The Initiation Of Lightning By Runaway Air Breakdown, Joseph R. Dwyer
The Initiation Of Lightning By Runaway Air Breakdown, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
A mechanism for lightning initiation by the sustained runaway breakdown of air is presented. Unlike earlior models that rely upon large cosmic-ray air showers, this mechanism uses the runaway electrons produced by the steady background of atmospheric cosmic-rays to amplify non-uniformities in the electric field. The ionization of air from the runaway electrons creates a region of discharge that propagates in the opposite direction of the electrons, enhancing the electric field in front of it to the point where a conventional breakdown can occur. As the discharged region grows, positron feedback can become important, dramatically increasing the flux of runaway …
X-Ray Bursts Produced By Laboratory Sparks In Air, Joseph R. Dwyer, Hamid K. Rassoul, Ziad H. Saleh, Martin A. Uman, J. Jerauld, J. Anderson Plumer
X-Ray Bursts Produced By Laboratory Sparks In Air, Joseph R. Dwyer, Hamid K. Rassoul, Ziad H. Saleh, Martin A. Uman, J. Jerauld, J. Anderson Plumer
Aerospace, Physics, and Space Science Faculty Publications
X-ray observations were made during fourteen 1.5 to 2.0 m high-voltage discharges in air produced by a 1.5 MV Marx circuit. All 14 discharges generated x-rays in the ∼30 to 150 keV range. The x-rays, which arrived in discrete bursts, less than 0.5 microseconds in duration, occurred from both positive and negative polarity rod-to-plane discharges as well as from small, 5-10 cm series spark gaps within the Marx generator. The x-ray bursts usually occurred when either the voltages across the gaps were the largest or were in the process of collapsing. The bursts are remarkably similar to the x-ray bursts …