509 research outputs found
Gourbin_Celestin_GRL_2023
No full text.fig figures made using the Monte Carlo + Particle-In-Cell model by P. Gourbin and S. Celestin, 2023, GRL.</p
Effects of the geomagnetic field on the beaming geometry of TGFs
No full textInternational audienceTerrestrial gamma-ray flashes (TGFs) are bursts of high-energy photons originating from the Earth's atmosphere in association with thunderstorm activity [e.g., Briggs et al., JGR, 118, 3805, 2013]. Although TGFs are believed to be produced inside thunderclouds (below 15 km altitude), the underlying physical mechanisms are still debated. Large-scale relativistic runaway electron avalanches (RREAs) along with relativistic feedback caused by positrons and photons have been proposed to occur in thunderclouds and to produce TGFs [e.g., Dwyer et al., Space Sci. Rev., 173, 133, 2012]. It has also been found that the production of thermal runaway electrons by stepping lightning leaders and their further acceleration could explain the TGF spectra and fluences for intracloud (IC) lightning electric potentials above ∼100 MV [Xu et al., GRL, 39, L08801, 2012; Celestin et al., JGR, 120, 2015]. In both scenarios, runaway electron avalanches take place and the related bremsstrahlung produces the TGF. The impact of the geomagnetic field on RREAs has been seldom studied (with the notable exceptions of Lehtinen et al. [JGR, 104, 24699, 1999], Babich et al. [Geom. Aeron., 44, 243, 2004] and Cramer et al. [AGU Fall Meeting, abstract AE33A-0472, San Francisco, USA, 2015]), particularly in view of recent knowledge acquired about TGF sources properties. In this work, we study the effects of the geomagnetic field on the runaway electron beam geometry in large-scale RREAs and in the vicinity of lightning leaders and the corresponding impact on TGF observations using analytical and numerical means
Effects of the geomagnetic field on the beaming geometry of TGFs
No full textInternational audienceTerrestrial gamma-ray flashes (TGFs) are bursts of high-energy photons originating from the Earth's atmosphere in association with thunderstorm activity [e.g., Briggs et al., JGR, 118, 3805, 2013]. Although TGFs are believed to be produced inside thunderclouds (below 15 km altitude), the underlying physical mechanisms are still debated. Large-scale relativistic runaway electron avalanches (RREAs) along with relativistic feedback caused by positrons and photons have been proposed to occur in thunderclouds and to produce TGFs [e.g., Dwyer et al., Space Sci. Rev., 173, 133, 2012]. It has also been found that the production of thermal runaway electrons by stepping lightning leaders and their further acceleration could explain the TGF spectra and fluences for intracloud (IC) lightning electric potentials above ∼100 MV [Xu et al., GRL, 39, L08801, 2012; Celestin et al., JGR, 120, 2015]. In both scenarios, runaway electron avalanches take place and the related bremsstrahlung produces the TGF. The impact of the geomagnetic field on RREAs has been seldom studied (with the notable exceptions of Lehtinen et al. [JGR, 104, 24699, 1999], Babich et al. [Geom. Aeron., 44, 243, 2004] and Cramer et al. [AGU Fall Meeting, abstract AE33A-0472, San Francisco, USA, 2015]), particularly in view of recent knowledge acquired about TGF sources properties. In this work, we study the effects of the geomagnetic field on the runaway electron beam geometry in large-scale RREAs and in the vicinity of lightning leaders and the corresponding impact on TGF observations using analytical and numerical means
Estimation of Physical Properties of Streamers in Transient Luminous Events from Non-Steady State Optical Emissions
No full textInternational audienceOptical emissions from sprite streamers are used to estimate peak electric fields and electron energies [e.g., Kuo et al., GRL, 32, L19103, 2005; Adachi et al., GRL, 33, L17803, 2006]. It has been shown that significant correction factors need to be used to account for the spatial shift between distributions of optical emissions in streamers and peak electric fields in their heads [Celestin and Pasko, GRL, 37, L07804, 2010]. The latter study involved the excited species N2(C3Πu) and N2+(B2Σu+), whose populations are considered to be in steady state. The species N2(C3Πu) and N2+(B2Σu+) are responsible for the second positive (2PN2) and first negative (1NN2+) band systems of N2 and N2+, respectively. In this work, we show how this technique can be extended to non-steady state optical emissions, such as those produced by N2(a1Πg) and N2(B3Πg) in the form of Lyman-Birge-Hopfield (LBH) and first positive (1PN2) band systems, respectively. Additionally, we simulate numerically downward propagating sprite streamers and their optical emissions for the following band systems: 1PN2, 2PN2, LBH, and 1NN2+, and show how they relate to specific physical properties. This study particularly focuses on improving analysis of observational results from the future missions ASIM (ESA) and TARANIS (CNES) that will detect various optical emissions produced by transient luminous events in the nadir
Using nadir-viewing photometric observations of sprites to infer properties of sprite streamers
No full textInternational audienceNadir-viewing geometry is well-suited for sprite observation as it allows to simultaneously detect electromagnetic and particles emissions over the event. The downside is the loss of the vertical resolution making it harder for the determination of physical quantities like streamer altitudes. Ihaddadene and Celestin [JGR, 112, 1000-1014, 2017] have developed a method to estimate the streamer peak electric field and the altitude from N2 and N +2 sprite streamers optical emission: Lyman-Birge-Hopfield (LBH) (a1Πg → X1 Σ+g ) (∼ 100nm - 260 nm ), the first positif system 1P N2 (B3Πg → A3 Σ+u ) (∼ 650nm - 1070 nm ), the second positif system 2P N2 (C3Πu → B3Π+g ) (∼ 330nm - 450 nm ), and the first negative system of the N+ 2 ion (1N N + 2 ) (B2Σu → X2Σ+ g ) (∼ 390nm - 430nm ). The instrument MCP on board the TARANIS space mission is dedicated to the observation of sprites through optical emissions by means of 2 cameras and 4 photometers. The detection of optical emissions by the four photometers is performed over specific bands: PH1 (160nm - 260 nm for LBH), PH2 (337± 5nm for 2PN2 ), PH3 (762 ± 5nm for 1P N2 ), and the lightning light by PH4 (600 nm - 900nm ). In this work, we improve the Ihaddadene and Celestin's [2017] method taking into account the radiative transfer of sprite emissions through the Earth's atmosphere and the instrumental response of MCP
Low frequency electromagnetic radiation from sprite streamers, Geophys
No full text[1] Sprites are mesospheric discharges that carry significant electrical currents and produce electromagnetic radiation observed typically in the extremely low (ELF) to ultra low (ULF) frequency bands. In this letter, we present the first theoretical estimates of the electromagnetic radiation produced by individual sprite streamers using simulation results from a plasma fluid model. It is demonstrated that the spectral content of the radiation produced by sprite streamers is a function of the air density N and the lightning-induced quasi-static ambient electric field E in the regions of space where the sprite streamers are propagating. We demonstrate that the exponential growth of the current in sprite streamers at 75 km would be preferentially associated with electromagnetic radiation in the frequency range from 0 and up to 300 kHz, consistently with the scaling of atmospheric air density. We further conjecture that the periodic branching of streamers may lead to a radiation spectrum enhancement in the very low (VLF) to low frequency (LF) range. Citation: Qin, J., S. Celestin, and V. P. Pasko (2012), Low frequency electromagnetic radiation from sprite streamers, Geophys. Res. Lett., 39, L22803
Estimation of Physical Properties of Streamers in Transient Luminous Events from Non-Steady State Optical Emissions
No full textInternational audienceOptical emissions from sprite streamers are used to estimate peak electric fields and electron energies [e.g., Kuo et al., GRL, 32, L19103, 2005; Adachi et al., GRL, 33, L17803, 2006]. It has been shown that significant correction factors need to be used to account for the spatial shift between distributions of optical emissions in streamers and peak electric fields in their heads [Celestin and Pasko, GRL, 37, L07804, 2010]. The latter study involved the excited species N2(C3Πu) and N2+(B2Σu+), whose populations are considered to be in steady state. The species N2(C3Πu) and N2+(B2Σu+) are responsible for the second positive (2PN2) and first negative (1NN2+) band systems of N2 and N2+, respectively. In this work, we show how this technique can be extended to non-steady state optical emissions, such as those produced by N2(a1Πg) and N2(B3Πg) in the form of Lyman-Birge-Hopfield (LBH) and first positive (1PN2) band systems, respectively. Additionally, we simulate numerically downward propagating sprite streamers and their optical emissions for the following band systems: 1PN2, 2PN2, LBH, and 1NN2+, and show how they relate to specific physical properties. This study particularly focuses on improving analysis of observational results from the future missions ASIM (ESA) and TARANIS (CNES) that will detect various optical emissions produced by transient luminous events in the nadir
Using nadir-viewing photometric observations of sprites to infer properties of sprite streamers
No full textInternational audienceNadir-viewing geometry is well-suited for sprite observation as it allows to simultaneously detect electromagnetic and particles emissions over the event. The downside is the loss of the vertical resolution making it harder for the determination of physical quantities like streamer altitudes. Ihaddadene and Celestin [JGR, 112, 1000-1014, 2017] have developed a method to estimate the streamer peak electric field and the altitude from N2 and N +2 sprite streamers optical emission: Lyman-Birge-Hopfield (LBH) (a1Πg → X1 Σ+g ) (∼ 100nm - 260 nm ), the first positif system 1P N2 (B3Πg → A3 Σ+u ) (∼ 650nm - 1070 nm ), the second positif system 2P N2 (C3Πu → B3Π+g ) (∼ 330nm - 450 nm ), and the first negative system of the N+ 2 ion (1N N + 2 ) (B2Σu → X2Σ+ g ) (∼ 390nm - 430nm ). The instrument MCP on board the TARANIS space mission is dedicated to the observation of sprites through optical emissions by means of 2 cameras and 4 photometers. The detection of optical emissions by the four photometers is performed over specific bands: PH1 (160nm - 260 nm for LBH), PH2 (337± 5nm for 2PN2 ), PH3 (762 ± 5nm for 1P N2 ), and the lightning light by PH4 (600 nm - 900nm ). In this work, we improve the Ihaddadene and Celestin's [2017] method taking into account the radiative transfer of sprite emissions through the Earth's atmosphere and the instrumental response of MCP
Sebastien Rale vs. New England: A Case Study of Frontier Conflict
No full textAuthor\u27s original abstract: A study was made of the Jesuit missionary, Sebastien Rale, and his role in New England-New France relations. French and English primary and secondary materials were examined to give the broadest possible view of the man and to place him in historical context.
It was found that Sebastien Rale was not an agent of New France. The conflicting opinions surrounding the mission of Norridgewock and the border war of the 1720\u27s were traced to the problems of Massachusetts-Abnaki relations. Rale\u27s frequent and testy letters to the government of the Bay Colony were blunt reactions to what he viewed as religious and territorial threats against his mission.
The frontier conflict between 1713 and 1722 was not the result of French Imperial policy. The French insisted that the Abnakis were allies but refused active participation in the Indians\u27 quarrel with New England. Policy was developed in Maine by the Jesuits. The missionaries were only secondarily interested in Quebec\u27s desire to prevent Massachusetts\u27 settlement of the Kennebec. With the declaration of war in July, 1722, however, the Jesuits left the Abnakis in the hands of the governor and the intendant of New France on whom the Indians relied for vital war supplies.
Finally, the controversial attack on Norridgewock was appraised. It was found that no secondary account had fully evaluated the sources. Examination led to the discovery of crucial inconsistencies in the primary accounts of New England. The French sources were found to be based on the understandably confused impressions of the fleeing Indians. In large measure the English sources present the more valid picture: the sudden attack, the panicked confusion, and Sebastien Rale dying with gun in hand. After Rale\u27s death the war drew to a close. Without Sebastien Rale\u27s persuasion and determination, the Abnakis were not able to present a united front against colonial expansion
Ambient dose equivalents in TGFs
No full textInternational audienceTerrestrial gamma-ray flashes (TGFs) are bursts of high-energy photons originating from the Earth's atmosphere in association with thunderstorm activity [e.g., Briggs et al., JGR, 118, 3805, 2013]. TGFs are associated with initial propagation stages of intracloud lightning, which represent the most frequent type of lightning discharges [e.g., Cummer et al., GRL, 42, 7792, 2015, and references therein]. TGFs are known to be produced inside common thunderclouds [e.g., Splitt et al., JGR, 115, A00E38, 2010] typically at altitudes ranging from 10 to 14 km [e.g., Cummer et al., GRL, 41, 8586, 2014]. The global TGF occurrence rate is estimated to be 400,000 per year concerning TGFs detectable by Fermi-GBM (Gamma ray Burst Monitor) [Briggs et al., 2013], but detailed analysis of satellite measurements [Østgaard et al., JGR, 117, A03327, 2012] and theoretical studies [Celestin et al., JGR, 120, 10712, 2015] suggest that it cannot be excluded that TGFs represent a part of a regular process taking place during the propagation of lightning discharges. It is important to assess the risk induced by TGFs for airline passengers and crews on board aircraft approaching thunderstorms. Dwyer et al. [JGR, 115, D09206, 2010] have estimated that if an aircraft were to find itself in the source electron beam giving rise to a TGF, passengers and crews might receive effective radiation doses above the regulatory limit depending on the beam diameter. Moreover, Tavani et al. [Nat. Hazards Earth Syst. Sci., 13, 1127, 2013] concluded that TGF-associated neutrons produced by photonuclear reactions would cause serious hazard on the aircraft avionics. In this work, we will present detailed simulation-based estimations of effective doses received by humans that would be irradiated by TGFs for various production altitudes and distances from the TGF source
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