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Author: Jérémy Riousset
Publisher: LAP Lambert Academic Publishing
ISBN: 9783848407200
Category :
Languages : en
Pages : 220
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Book Description
Blue jets and gigantic jets are transient luminous events in the middle atmosphere that form when conventional lightning leaders escape upward from thundercloud tops and propagate toward the lower ionosphere. Petrov and Petrova [1999] first expressed that jets could be the extension of classic lightning discharges initiated within the cloud boundaries. This dissertation demonstrates the fundamental physical similarities between the various electrical discharges known to occur in the thundercloud due to local and global charge imbalances. How charge imbalances form in the thundercloud has been first suggested by Wilson [1921], but their impact on the occurrence of blue and gigantic jets was not explored. This work shows that the accumulation of screening charges near the thundercloud top produces a charge configuration leading to the initiation of blue jets, and the effective mixing of these charges with the upper thundercloud charge to that of gigantic jets. Also, the physics of lightning and jets, and many of the small-scale features observed in jets can be interpreted in terms of streamers (needle-shaped filaments of ionization), and are further explored via numerical modeling.
Author: Jérémy Riousset
Publisher: LAP Lambert Academic Publishing
ISBN: 9783848407200
Category :
Languages : en
Pages : 220
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Book Description
Blue jets and gigantic jets are transient luminous events in the middle atmosphere that form when conventional lightning leaders escape upward from thundercloud tops and propagate toward the lower ionosphere. Petrov and Petrova [1999] first expressed that jets could be the extension of classic lightning discharges initiated within the cloud boundaries. This dissertation demonstrates the fundamental physical similarities between the various electrical discharges known to occur in the thundercloud due to local and global charge imbalances. How charge imbalances form in the thundercloud has been first suggested by Wilson [1921], but their impact on the occurrence of blue and gigantic jets was not explored. This work shows that the accumulation of screening charges near the thundercloud top produces a charge configuration leading to the initiation of blue jets, and the effective mixing of these charges with the upper thundercloud charge to that of gigantic jets. Also, the physics of lightning and jets, and many of the small-scale features observed in jets can be interpreted in terms of streamers (needle-shaped filaments of ionization), and are further explored via numerical modeling.
Author: Jérémy A. Riousset
Publisher:
ISBN:
Category :
Languages : en
Pages : 206
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Book Description
Author: Caitano Da Silva
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The work presented in this dissertation is dedicated to the investigation of leader discharge mechanisms in lightning and transient luminous events. We introduce two new numerical models of the leader process that capture its onset and propagation, as briefly described below.The first theoretical model simulates air heating and streamer-to-leader transition in gas discharges. The model accounts for all physical processes known to play a role in the conversion of a streamer corona to a leader channel. Detailed discussion on the role of electron detachment in the development of the thermal-ionizational instability that triggers the spark development in short air gaps is presented. The dynamics of fast heating by quenching of excited electronic states is discussed and the scaling of its main channels with ambient air density is quantified. The developed model is employed to study the streamer-to-leader transition process and to obtain its scaling with ambient air density. The introduced methodology for estimation of leader speeds is based on the assumption that the propagation of a leader is limited by the air heating of every newly-formed leader section. It is demonstrated that the streamer-to-leader transition time has an inverse-squared dependence on the ambient air density at near-ground pressures, in agreement with similarity laws for Joule heating in a streamer channel. Model results indicate that a deviation from this similarity scaling occurs at very-low air densities, where the rate of electronic power deposition is balanced by the channel expansion, and air heating from quenching of excited electronic states is very inefficient. These findings place a limit on the maximum altitude at which a hot and highly-conducting lightning leader channel can be formed in the Earth's atmosphere. This result is important for understating of the gigantic jet discharges between thundercloud tops and the lower ionosphere. Our simulations of leader propagation at stratospheric altitudes demonstrate that initial speeds of gigantic jets are consistent with the leader propagation mechanism, and that the observed acceleration in gigantic jets can be attributed to the expansion of its streamer zone in a medium of exponentially-decreasing air density. This process defines the existence of an altitude at which the streamer zone becomes so long that it dynamically extends all the way to the ionosphere. We extend the air heating model to simulate the effects of strong currents flowing in sprites in the mesosphere. We show that fast air heating (due to quenching of excited electronic states) in sprite cores can produce >0.01 Pa pressure perturbations on the ground, observed in association with sprites. The second theoretical model simulates the electromagnetic radiation generated during the initial breakdown stage of lightning discharges. We use this model to describe in detail how the leader discharge dynamics generates the so-called initial breakdown pulses (IBPs) and narrow bipolar events (NBEs) observed with multi-station electric field change sensors on the ground. IBPs have been correlated with individual bursts of light that appear to be illuminations of a lightning leader channel; as a flash evolves the location of IBP sources inside the cloud coincides with the position of negative leaders as determined by a VHF lightning mapping system. NBEs are electric field signatures with broadband waveforms resembling classic IBPs in both amplitude and duration. Nonetheless, NBEs are quite peculiar in the sense that very infrequently they are followed by conventional lightning processes. Only a small fraction of positive-polarity NBEs happen as the first event in an otherwise regular intracloud lightning discharge. Typically, the initiator-type of NBEs has no difference with other NBEs that did not start lightning, except for the fact that they occur deeper inside the thunderstorm (i.e., at lower altitudes). In this dissertation we propose that IBPs and NBEs are the electromagnetic transients associated with the sudden (i.e., stepwise) elongation of the initial negative leader extremity in the thunderstorm electric field. To demonstrate our hypothesis we use a novel model of the leader electrodynamics. It consists of a generalization of electrostatic and transmission-line approximations existing in the refereed literature. We demonstrate how the IBP and NBE waveform characteristics directly reflect the properties of the bidirectional lightning leader (such as step length, for example) and amplitude of the thunderstorm electric field.
Author: Martin Füllekrug
Publisher: Springer Science & Business Media
ISBN: 9781402046285
Category : Science
Languages : en
Pages : 420
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Book Description
Particularly intense lightning discharges can produce transient luminous events above thunderclouds, termed sprites, elves and jets. These short lived optical emissions in the mesosphere can reach from the tops of thunderclouds up to the ionosphere; they provide direct evidence of coupling from the lower atmosphere to the upper atmosphere. Sprites are arguably the most dramatic recent discovery in solar-terrestrial physics. Shortly after the first ground based video recordings of sprites, observations on board the Space Shuttle detected sprites and elves occurring all around the world. These reports led to detailed sprite observations in North America, South America, Australia, Japan, and Europe. Subsequently, sprites were detected from other space platforms such as the International Space Station and the ROCSAT satellite. During the past 15 years, more than 200 contributions on sprites have been published in the scientific literature to document this rapidly evolving new research area.
Author: Pingzhi Wang
Publisher: Nova Publishers
ISBN: 9781600219870
Category : Science
Languages : en
Pages : 434
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Book Description
This book presents the latest results on solar-stellar research and the study of solar terrestrial physics. It includes all aspects of solar physics, ranging from the internal structure of the sun and its evolution, to outer corona and solar wind in interplanetary space.
Author: B. A. Jubran
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author:
Publisher:
ISBN:
Category : Physics
Languages : en
Pages : 920
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Book Description
Author: Rushi Ghadawala
Publisher: BoD – Books on Demand
ISBN: 9535103806
Category : Technology & Engineering
Languages : en
Pages : 280
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Book Description
"Advances in Spacecraft Systems and Orbit Determinations", discusses the development of new technologies and the limitations of the present technology, used for interplanetary missions. Various experts have contributed to develop the bridge between present limitations and technology growth to overcome the limitations. Key features of this book inform us about the orbit determination techniques based on a smooth research based on astrophysics. The book also provides a detailed overview on Spacecraft Systems including reliability of low-cost AOCS, sliding mode controlling and a new view on attitude controller design based on sliding mode, with thrusters. It also provides a technological roadmap for HVAC optimization. The book also gives an excellent overview of resolving the difficulties for interplanetary missions with the comparison of present technologies and new advancements. Overall, this will be very much interesting book to explore the roadmap of technological growth in spacecraft systems.
Author: Robert V. Wilson
Publisher:
ISBN:
Category :
Languages : en
Pages : 24
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Book Description
Three-dimensional turbulent jets with rectangular cross-section are simulated with a finite-difference numerical method. The full Navier-Stokes equations are solved at low Reynolds numbers, whereas at the high Reynolds numbers filtered forms of the equations are solved along with a subgrid scale model to approximate effects of the unresolved scales. A 2-N storage, third-order Runge-Kutta scheme is used for temporal discretization and a fourth-order compact scheme is used for spatial discretization. Computations are performed for different inlet conditions which represent different types of jet forcing. The phenomenon of axis-switching is observed, and it is confirmed that this is based on self-induction of the vorticity field. Budgets of the mean streamwise velocity show that convection is balanced by gradients of the Reynolds stresses and the pressure.
Author: Jonathan Ferreira
Publisher: Springer
ISBN: 3540680357
Category : Science
Languages : en
Pages : 230
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Book Description
This volume presents the edited lecture notes of the First JETSET School on Jets from Young Stars: Models and Constraints, held by the Marie Curie Research and Training Network on JET Simulations, Experiments and Theory. The first half of the book is devoted to general observational constraints. The second section is devoted to theoretical knowledge of magneto-hydrodynamic processes pertinent to the jet launching mechanism in young stars.
