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Full-Text Articles in Geophysics and Seismology
Do Cosmic Ray Air Showers Initiate Lightning?: A Statistical Analysis Of Cosmic Ray Air Showers And Lightning Mapping Array Data, B. M. Hare, Hamid K. Rassoul
Do Cosmic Ray Air Showers Initiate Lightning?: A Statistical Analysis Of Cosmic Ray Air Showers And Lightning Mapping Array Data, B. M. Hare, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
It has been argued in the technical literature, and widely reported in the popular press, that cosmic ray air showers (CRASs) can initiate lightning via a mechanism known as relativistic runaway electron avalanche (RREA), where large numbers of high-energy and low-energy electrons can, somehow, cause the local atmosphere in a thundercloud to transition to a conducting state. In response to this claim, other researchers have published simulations showing that the electron density produced by RREA is far too small to be able to affect the conductivity in the cloud sufficiently to initiate lightning. In this paper, we compare 74 days …
Modification Of The Lower Ionospheric Conductivity By Thunderstorm Electrostatic Fields, Mohammad A. Salem, Ningyu Liu, Hamid K. Rassoul
Modification Of The Lower Ionospheric Conductivity By Thunderstorm Electrostatic Fields, Mohammad A. Salem, Ningyu Liu, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
This paper reports a modeling study of the modifications of the nighttime lower ionospheric conductivity by electrostatic fields produced by underlying thunderstorms. The model used combines Ohm's law with a simplified lower ionospheric ion chemistry model to self-consistently calculate the steady state nighttime conductivity above a thunderstorm. The results indicate that although the electron density is generally increased, the lower ionospheric conductivity can be reduced by up to 1-2 orders of magnitude because electron mobility is significantly reduced due to the electron heating effect. For a typical ionospheric density profile, the resulting changes in the reflection heights of extremely low …
Ground Detection Of Terrestrial Gamma Ray Flashes From Distant Radio Signals, Fanchao Lyu, Eric Cramer
Ground Detection Of Terrestrial Gamma Ray Flashes From Distant Radio Signals, Fanchao Lyu, Eric Cramer
Aerospace, Physics, and Space Science Faculty Publications
Terrestrial gamma ray flashes (TGFs) are brief bursts of energetic gammy-ray photons generated during thunderstorms, which have been detected almost exclusively by satellite-based instruments. Here we present three lines of evidence which includes the three out of three simultaneously observed pairs, the same occurrence contexts, and the consistent estimated occurrence rate, which indicate a direct relationship between a subset of TGFs and a class of energetic radio signal easily detectable by ground-based sensors. This connection indicates that these gamma ray and radio emissions are two views of the same phenomenon and further enable detection of these TGFs from ground distant …
Observation-Constrained Modeling Of The Ionospheric Impact Of Negative Sprites, Ningyu Liu, Levi D. Boggs, Steven A. Cummer
Observation-Constrained Modeling Of The Ionospheric Impact Of Negative Sprites, Ningyu Liu, Levi D. Boggs, Steven A. Cummer
Aerospace, Physics, and Space Science Faculty Publications
This paper reports observation and modeling of five negative sprites occurring above two Florida thunderstorms. The sprites were triggered by unusual types of negative cloud-to-ground (CG) lightning discharges with impulse charge moment change ranging from 600 to 1300 C km and charge transfer characterized by a timescale of 0.1-0.2 ms. The negative sprite typically consists of a few generally vertical elements that each contain a bright core and dimmer streamers extending from the core in both downward and upward directions. Modeling results using the measured charge moment change waveforms indicate that the lower ionosphere was significantly modified by the CGs …
Spectral Properties Of Titan’S Impact Craters Imply Chemical Weathering Of Its Surface, Catherine D. Neish
Spectral Properties Of Titan’S Impact Craters Imply Chemical Weathering Of Its Surface, Catherine D. Neish
Aerospace, Physics, and Space Science Faculty Publications
We examined the spectral properties of a selection of Titan's impact craters that represent a range of degradation states. The most degraded craters have rims and ejecta blankets with spectral characteristics that suggest that they are more enriched in water ice than the rims and ejecta blankets of the freshest craters on Titan. The progression is consistent with the chemical weathering of Titan's surface. We propose an evolutionary sequence such that Titan's craters expose an intimate mixture of water ice and organic materials, and chemical weathering by methane rainfall removes the soluble organic materials, leaving the insoluble organics and water …
Effects Of Small Thundercloud Electrostatic Fields On The Ionospheric Density Profile, Mohammad A. Salem, Ningyu Liu, Hamid K. Rassoul
Effects Of Small Thundercloud Electrostatic Fields On The Ionospheric Density Profile, Mohammad A. Salem, Ningyu Liu, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
Small electrostatic fields of values not strong enough to activate electron impact ionization, attachment, and detachment processes can be established in the upper atmosphere by underlying thunderstorms. This paper investigates their effects on the ionospheric densities by using a simplified ion chemistry model. The modeling results indicate that under the steady state condition, the nighttime electron density profile can be reduced by up to ∼40% or enhanced by a factor of up to ∼6 because of the variation of the three-body electron attachment rate constant with the electric field.
First Images Of Thunder: Acoustic Imaging Of Triggered Lightning, M. A. Dayeh, R. Lucia, Hamid K. Rassoul
First Images Of Thunder: Acoustic Imaging Of Triggered Lightning, M. A. Dayeh, R. Lucia, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
An acoustic camera comprising a linear microphone array is used to image the thunder signature of triggered lightning. Measurements were taken at the International Center for Lightning Research and Testing in Camp Blanding, FL, during the summer of 2014. The array was positioned in an end-fire orientation thus enabling the peak acoustic reception pattern to be steered vertically with a frequency-dependent spatial resolution. On 14 July 2014, a lightning event with nine return strokes was successfully triggered. We present the first acoustic images of individual return strokes at high frequencies (>1kHz) and compare the acoustically inferred profile with optical …
Formation Of Sprite Streamers At Subbreakdown Conditions From Ionospheric Inhomogeneities Resembling Observed Sprite Halo Structures, Burcu C. Kosar, Ningyu Liu, Hamid K. Rassoul
Formation Of Sprite Streamers At Subbreakdown Conditions From Ionospheric Inhomogeneities Resembling Observed Sprite Halo Structures, Burcu C. Kosar, Ningyu Liu, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
Modeling results of sprite streamer formation from large ionospheric inhomogeneities or patches (several tens to hundreds of meter wide) indicate that positive streamers can be initiated at subbreakdown conditions from the inhomogeneities with a density comparable to sprite halo densities. For spherical patches with a given radius, the minimum density required for streamer initiation decreases with increasing ambient field. For a given density, the minimum size of the inhomogeneity decreases with increasing ambient field. The modeling results on the associated optical emissions show that a luminous spherical-like cap appears around the lower tip of the ionization patch before streamer initiation, …
Properties Of The Thundercloud Discharges Responsible For Terrestrial Gamma-Ray Flashes, Joseph R. Dwyer, Ningyu Liu, Hamid K. Rassoul
Properties Of The Thundercloud Discharges Responsible For Terrestrial Gamma-Ray Flashes, Joseph R. Dwyer, Ningyu Liu, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
The source of terrestrial gamma-ray flashes (TGFs) has been an active area of research since their discovery by Compton Gamma-Ray Observatory/Burst and Transient Source Experiment in 1994. These intense bursts of gamma rays originate within thunderclouds via the rapid production of relativistic runaway electrons, accelerated by thundercloud/lightning electric fields to multi-MeV energies. Recent studies have shown that electrical discharges within thunderclouds caused by these runaway electrons can generate currents that rival those of lightning and so could serve as an alternative discharge path for thunderclouds. In particular, the discharges responsible for TGFs produce some of the largest amplitude VLF-LF radio …
The Rarity Of Terrestrial Gamma-Ray Flashes, D. M. Smith, Michael E. Splitt, Steven M. Lazarus, W. Ulrich, Jospeh R. Dwyer
The Rarity Of Terrestrial Gamma-Ray Flashes, D. M. Smith, Michael E. Splitt, Steven M. Lazarus, W. Ulrich, Jospeh R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
We report on the first search for Terrestrial Gamma-ray Flashes (TGFs) from altitudes where they are thought to be produced. The Airborne Detector for Energetic Lightning Emissions (ADELE), an array of gamma-ray detectors, was flown near the tops of Florida thunderstorms in August/September 2009. The plane passed within 10 km horizontal distance of 1213 lightning discharges and only once detected a TGF. If these discharges had produced TGFs of the same intensity as those seen from space, every one should have been seen by ADELE. Separate and significant nondetections are established for intracloud lightning, negative cloud-to-ground lightning, and narrow bipolar …
Electron-Positron Beams From Terrestrial Lightning Observed With Fermi Gbm, Michael S. Briggs, Joseph R. Dwyer
Electron-Positron Beams From Terrestrial Lightning Observed With Fermi Gbm, Michael S. Briggs, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
Terrestrial Gamma-ray Flashes (TGFs) are brief pulses of energetic radiation observed in low-earth orbit. They are associated with thunderstorms and lightning and have been observed both as gamma-ray and electron flashes depending on the position of the spacecraft with respect to the source. While gamma-ray TGFs are detected as short pulses lasting less than 1 ms, most TGFs seen by the Fermi Gamma-ray Burst Monitor (GBM) with durations greater than 1 ms are, instead, the result of electrons traveling from the sources along geomagnetic field lines. We perform spectral analysis of the three brightest electron TGFs detected by GBM and …
Remote Measurements Of Thundercloud Electrostatic Fields, Joseph R. Dwyer, Martin A. Uman, Hamid K. Rassoul
Remote Measurements Of Thundercloud Electrostatic Fields, Joseph R. Dwyer, Martin A. Uman, Hamid K. Rassoul
Aerospace, Physics, and Space Science Faculty Publications
Analytical and numerical models of the radio frequency emissions produced by relativistic runaway electron avalanches initiated by cosmic ray extensive air showers are presented. It is found that single-point measurements of the distant electromagnetic fields allow the remote determination of the electrostatic field in the runaway electron avalanche region. For instance, it is possible to use ground-based and/or remote airborne measurements of the radio frequency pulses from the runaway electron avalanches to map the magnitudes and directions of the electrostatic field within a thundercloud for regions with electric fields above the runaway avalanche threshold. Such measurements, which are difficult to …
Source Mechanisms Of Terrestrial Gamma-Ray Flashes, Joseph R. Dwyer
Source Mechanisms Of Terrestrial Gamma-Ray Flashes, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
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 of MeV gamma rays likely originate much deeper in the atmosphere than previously inferred from Burst and Transient Source Experiment (BATSE) data, with the source altitude <21 km. Using existing measurements of the intensity and duration of BATSE and RHESSI TGFs, along with limits on the electric field set by the relativistic feedback mechanism involving backward propagating positrons and x-rays, it is found that TGFs cannot be produced by relativistic runaway electron avalanches acting on natural background radiation or extensive cosmic-ray air showers alone, as has been assumed by many previous models. Instead, the energetic seed particle production most likely involves either relativistic feedback or runaway electron production in the strong electric fields associated with lightning lead or streamers, similar to the energetic radiation observed on the ground from lightning.
X-Ray Bursts Associated With Leader Steps In Cloud-To-Ground Lightning, Joseph R. Dwyer, Hamid K. Rassoul, M. Al-Dayeh, Lee Caraway, A. Chrest, Brian F. Wright, E. Kozak
X-Ray Bursts Associated With Leader Steps In Cloud-To-Ground Lightning, Joseph R. Dwyer, Hamid K. Rassoul, M. Al-Dayeh, Lee Caraway, A. Chrest, Brian F. Wright, E. Kozak
Aerospace, Physics, and Space Science Faculty Publications
X-ray and electric field measurements were made during five nearby negative natural lightning strikes in north central Florida during the summer of 2004. The observed X-ray emission typically was detected ∼1 ms before the first return stroke, during the stepped-leader phase, and had energies extending up to a few hundred keV. The X rays were produced in discrete, intense bursts emitted in coincidence with the formation of the leader steps, demonstrating unambiguously that the source of lightning X rays is closely related to the stepping process. The X-ray emission from lightning stepped leaders is found to be remarkably similar to …
Implications Of X-Ray Emission From Lightning, Joseph R. Dwyer
Implications Of X-Ray Emission From Lightning, Joseph R. Dwyer
Aerospace, Physics, and Space Science Faculty Publications
Dwyer et al. [2003, 2004a] recently reported measurements of bursts of x-rays, with energies up to ∼250 keV, originating from dart leaders and possibly the return strokes of rocket-triggered lightning. In this paper, these x-ray observations are compared with the relativistic runaway electron avalanche (RREA) model. It is found that for dart leaders the standard RREA model is inconsistent with the observed spectrum and flux of the x-ray emission. This result implies that the cold runaway electron model may be applicable to dart leaders. In this model, runaway electrons are directly accelerated out of the bulk electron population, produced by …
Nonlinear Guiding Center Theory Of Perpendicular Diffusion: General Properties And Comparison With Observation, John W. Bieber, William H. Matthaeus, Andreas Shalchi, Gang Qin
Nonlinear Guiding Center Theory Of Perpendicular Diffusion: General Properties And Comparison With Observation, John W. Bieber, William H. Matthaeus, Andreas Shalchi, Gang Qin
Aerospace, Physics, and Space Science Faculty Publications
A nonlinear guiding center (NLGC) theory for diffusion of charged particles perpendicular to the mean magnetic field was recently proposed. Here, we draw attention to a number of attractive features of this theory: (1) The theory provides a natural mechanism to connect the perpendicular mean free path with the parallel mean free path. In fact, the parallel mean free path is the only particle property required to determine uniquely the perpendicular mean free path. (2) Under a broad range of conditions, the theory predicts that the perpendicular mean free path will be of order one percent or a few percent …
On The Origin Of Reverse Polarity Tcrs, Mark B. Moldwin, Michael R. Collier, James A. Slavin, Adam Szabo
On The Origin Of Reverse Polarity Tcrs, Mark B. Moldwin, Michael R. Collier, James A. Slavin, Adam Szabo
Aerospace, Physics, and Space Science Faculty Publications
Reverse polarity, or South-then-North (SN) bipolar, traveling compression regions (SN TCRs) are often observed in the Earth's magnetotail lobes. These events have been interpreted as either slowly earthward propagating "proto-plasmoids" during extremely quiet geomagnetic conditions, or due to pressure pulses in the solar wind or magnetosheath compressing the magnetotail. This study presents a survey of 21 IMP 8 observations of SN TCRs and the corresponding solar wind pressure conditions as measured by WIND. We found that solar wind or magnetosheath pressure pulses nicely explain most (17), though not all, of the SN TCR observations. Therefore, it appears that both explanations …
Evidence Of Different Magnetotail Responses To Small Solar Wind Pressure Pulses Depending On Imf Bz Polarity, Mark B. Moldwin, S. S. Mayerberger, Hamid K. Rassoul, Michael R. Collier, Ronald P. Lepping, James A. Slavin, Adam Szabo
Evidence Of Different Magnetotail Responses To Small Solar Wind Pressure Pulses Depending On Imf Bz Polarity, Mark B. Moldwin, S. S. Mayerberger, Hamid K. Rassoul, Michael R. Collier, Ronald P. Lepping, James A. Slavin, Adam Szabo
Aerospace, Physics, and Space Science Faculty Publications
The response of the magnetotail to small flux rope associated pressure pulses depends on the IMF Bz polarity. Clear and large amplitude magnetotail reverse polarity South-then-North traveling compression regions (SN TCRs) are observed when the pressure pulse is associated with the northward IMF interval of the flux rope. These tail signatures correspond to small-scale (<10 minute duration) pulses of the solar wind dynamic pressure located in front of and within the small-scale flux ropes. Pressure pulses associated with IMF Bz southward are either absent or give rise to smaller amplitude compressions and less systematic lobe Bz rotations. These results suggest that the orientation of the IMF Bz plays a critical role in modulating the magnetotail response to solar wind dynamic pressure pulses.
Small-Scale Magnetic Flux Ropes In The Solar Wind, M. B. Moldwin, S. Ford, Ronald P. Lepping, James A. Slavin, Adam Szabo
Small-Scale Magnetic Flux Ropes In The Solar Wind, M. B. Moldwin, S. Ford, Ronald P. Lepping, James A. Slavin, Adam Szabo
Aerospace, Physics, and Space Science Faculty Publications
Small-scale magnetic flux ropes have been discovered in the solar wind at 1 AU in observations from the IMP 8 and WIND spacecraft. These small magnetic structures (diameter of 270 R(E), on average) have some similar properties to magnetic clouds (diameters of 0.2 -0.3 AU or about 6000 - 8000 R(E)), which are well known large-scale magnetic flux ropes, but have durations of 10s of minutes as opposed to many hours or days for most magnetic clouds. The presence of these small helical field structures suggests that solar wind flux ropes may have a wide-range of scale sizes, or possibly …