[1] In the present paper, we demonstrate that the exponential expansion of streamers propagating in fields higher than the critical fields for stable propagation of streamers of a given polarity leads to the exponential growth of electric potential differences in streamer heads. These electric potential differences are directly related to the energy that thermal runaway electrons can gain once created. Using full energy range relativistic Monte Carlo simulations, we show that the exponential growth of potential differences in streamers gives rise to the production of runaway electrons with energies as high as ∼100 keV, with most of electrons residing in energy range around several tens of keVs. We apply these concepts in the case of lightning stepped leaders during the stage of negative corona flash. The computation of electric field produced by stepped leaders demonstrates for the first time that those energetic electrons are capable of further acceleration up to the MeV energies. Moreover, the flux of runaway electrons produced by streamers suggests that stepped leaders produce a considerable number of energetic electrons, which is in agreement with the number of energetic photons observed from satellites in terrestrial gamma ray flashes (TGFs). The results suggest that previously proposed process of relativistic runaway electron avalanche is difficult to sustain in the low‐electric fields observed in thunderclouds and is generally not needed for explanation of TGFs. The present work also gives insights on relations between physical properties of energetic electrons produced in streamers and the internal electrical properties of streamer discharges, which can further help development and interpretation of X‐ray diagnostics of these discharges.

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Energy and fluxes of thermal runaway electrons produced by exponential growth of streamers during the stepping of lightning leaders and in transient luminous events

The knowledge of the initiation and propagation of an upward moving connecting leader in the presence of a downward moving lightning stepped leader is a must in the determination of the lateral attraction distance of a lightning flash by any grounded structure. Even though different models that simulate this phenomenon are available in the literature, they do not take into account the latest developments in the physics of leader discharges. The leader model proposed here simulates the advancement of positive upward leaders by appealing to the presently understood physics of that process. The model properly simulates the upward continuous progression of the positive connecting leaders from its inception to the final connection with the downward stepped leader (final jump). Thus, the main physical properties of upward leaders, namely the charge per unit length, the injected current, the channel gradient and the leader velocity are self-consistently obtained. The obtained results are compared with an altitude triggered lightning experiment and there is good agreement between the model predictions and the measured leader current and the experimentally inferred spatial and temporal location of the final jump. It is also found that the usual assumption of constant charge per unit length, based on laboratory experiments, is not valid for lightning upward connecting leaders.

/pdf/a-self-consistent-upward-leader-propagation-model-1g984gcjx8.pdf

A self-consistent upward leader propagation model

Display Omitted In this paper a novel meta-heuristic optimization algorithm known as lightning LAPO is proposed.The purposed method is free from any parameter tuning.Two phase solution updating in each iteration increase the balancing of exploration and exploitation. In this article, A novel nature-inspired optimization algorithm known as Lightning Attachment Procedure Optimization (LAPO) is proposed. The proposed approach mimics the lightning attachment procedure including the downward leader movement, the upward leader propagation, the unpredictable trajectory of lightning downward leader, and the branch fading feature of lightning. Final optimum result would be the lightning striking point. The proposed method is free from any parameter tuning and it is rarely stuck in the local optimum points. To evaluate the proposed algorithm, 29 mathematical benchmark functions are employed and the results are compared to those of 9 high quality well-known optimization methods The results of the proposed method are compared from different points of views, including quality of the results, convergence behavior, robustness, and CPU time consumption. Superiority and high quality performance of the proposed method are demonstrated through comparing the results. Moreover, the proposed method is also tested by five classical engineering design problems including tension/compression spring, welded beam, pressure vessel designs, Gear train design, and Cantilever beam design and a high constraint optimization problem known as Optimal Power Flow (OPF) which is a high constraint electrical engineering problem. The excellence performance of the proposed method in solving the problems with large number of constraints and also discrete optimization problems are also concluded from the results of the six engineering problem.

A novel physical based meta-heuristic optimization method known as Lightning Attachment Procedure Optimization

Field and Analytical Studiesof Transmission LineShielding

A study is conducted of the principal chemical effects induced by the passage of a single sprite streamer through the mesosphere at an altitude of 70 km. Recent high-speed imaging of sprite streamers has revealed them to comprise bright (1-100 GR), compact (decameter-scale) heads moving at ∼10 7 m s -1 . On the basis of these observations, a quantitative model of the chemical dynamics of the streamer head and trailing region is constructed using a nonlinear coupled kinetic scheme of 80+ species and 800+ reactions. In this initial study, chemical processes related to currents in the trailing column and to vibrational kinetics of N 2 and O 2 are not included. The descending streamer head impulsively (T ∼ 10 μs) ionizes the gas (fractional ionization density ∼10 -9 ), leaving in its trail a large population of ions, and dissociated and excited neutral byproducts. Electrons created by ionization within the head persist within the trailing column for about 1 s, with losses occurring approximately equally by dissociative attachment with ambient O 3 , and by dissociative recombination with the positive ion cluster N 2 O + 2 . The ion cluster is produced within the trailing channel by a three-step process involving ionization of N 2 , N + 2 charge exchange with O 2 , and finally three-body creation of N 2 O + 2 . On the basis of simulation results, it is concluded that the observed reignition of sprites most likely originates in remnant patches of cold electrons in the decaying streamer channels of a previous sprite. Relatively large populations (fractional densities ∼10 -9 -10 -8 ) of the metastable species O( 1 D), O( 1 S), N( 2 D), O 2 (a 1 Δ g ), O 2 (b 1 Σ + g ), N 2 (A 3 Σ + u ), and N 2 (a' 1 Σ - u ) are created in the streamer head. The impulsive creation of these species initiates numerous coupled reaction chains, with most of the consequent effects being of a transient nature persisting for less than 1 s. These include weak (∼1 kR), but possibly detectable, OI 557.7 nm and O 2 (b 1 Σ + g → X 3 Σ - g ) Atmospheric airglow emissions. Neutral active species created in the greatest abundance (fractional densities > 10 -8 ) are N 2 (X 1 Σ + g , ν), O( 3 P), N( 4 S), and O 2 (a 1 Δ g ), which, because of the absence of readily available chemical dissipation channels, persist for longer than 100s of seconds. Other long-lived (>1000 s) effects are very weak (∼1-10 R) OH(X 2 Π, ν = 6...9 - Δν) Meinel emissions produced by O( 3 P)-enhanced OH catalysis and O 2 (a 1 Δ g → X 3 Σ - g ) Infrared Atmospheric emissions. Short-lived (∼100 s) populations of hydrated positive ions and negative ion clusters are also created in the streamer trail. Electron impact dissociated N( 2 D) interacts with O 2 to create a long-lived (>1000 s) increase (fractional enhancement ∼75%) of the ambient NO density within the streamer channel, for a net production of ∼5 x 10 19 NO molecules for the streamer as a whole. It is suggested that in addition to the optical emissions from electron-impact excited electronic states of N 2 , a substantial portion of the spectrum may be due to chemiluminescent processes derived from vibrational kinetics of nitrogen.

Plasma Chemistry of Sprite Streamers

In this paper, a generalized leader inception model is proposed. It is based on an iterative geometrical analysis of the background potential distribution of an earthed structure to simulate the first meters of propagation of an upward connecting leader. By assuming a static field approach, the leader stabilization fields and the striking distances were computed for a lightning rod and for a building. The obtained results were compared with the existing leader inception criteria. Furthermore, in order to validate the model, the leader inception condition was computed for a triggered lightning experiment. Excellent agreement with the experimental results was obtained. The present model has several advantages in comparison with the existing leader inception criteria. One of them is related to the fact that the proposed model can be used to analyze the effect of the space charge on the upward leader inception.

A simplified physical model to determine the lightning upward connecting leader inception

The evaluation of the upward connecting leader inception from a grounded structure has generally been performed neglecting the effect of the propagation of the downward stepped leader. Nevertheless, field observations suggest that the space charge produced by streamer corona and aborted upward leaders during the approach of the downward lightning leader can influence significantly the initiation of stable upward positive leaders. Thus, a physical leader inception model is developed, which takes into account the electric field variations produced by the descending leader during the process of inception. Also, it accounts for the shielding effect produced by streamer corona and unstable leaders formed before the stable leader inception takes place. The model is validated by comparing its predictions with the results obtained in long gap experiments and in an altitude triggered lightning experiment. The model is then used to estimate the leader inception conditions for free standing rods as a function of tip radius and height. It is found that the rod radius slightly affects the height of the downward leader tip necessary to initiate upward leaders. Only an improvement of about 10% on the lightning attractiveness can be reached by using lightning rods with an optimum radius. Based on the obtained results, the field observations of competing lightning rods are explained. Furthermore, the influence of the average stepped leader velocity on the inception of positive upward leaders is evaluated. The results obtained show that the rate of change of the background electric field produced by a downward leader descent largely influences the conditions necessary for upward leader initiation. Estimations of the leader inception conditions for the upper and lower limit of the measured values of the average downward lightning leader velocity differ by more than 80%. In addition, the striking distances calculated taking into account the temporal change of the background field are significantly larger than the ones obtained assuming a static downward leader field. The estimations of the present model are also compared with the existing leader inception models and discussed.

/pdf/time-dependent-evaluation-of-the-lightning-upward-connecting-1g39ll7cej.pdf

Time dependent evaluation of the lightning upward connecting leader inception

The inception of leader discharges in long air gaps at atmospheric pressure is simulated with a thermo-hydrodynamic model and a detailed kinetic scheme for N2/O2/H2O mixtures. In order to investiga ...

https://iopscience.iop.org/article/10.1088/1361-6463/aa7c71/pdf

Gas heating dynamics during leader inception in long air gaps at atmospheric pressure

A study undertaken to measure the resistance of spark channels in air with two different current waveforms is presented. In one experiment, the spark was created by a Marx generator. In this case, the gap length was maintained at 12.8 cm, and the current flowing through the spark had a peak current lying in the range of 0.2-2.2 kA. The decay time of the current was larger than 100 mus. In the other experiment, the spark was created by a current generator. In that experiment, the gap length was maintained at 1 cm, and the current flowing through the spark had peak-current amplitudes in the range of 35-48 kA. The decay time of the current was larger than 500 mus. The results show that the resistance of spark channels initially decreases, reaches a minimum value, and then recovers as the current in the spark gap decreases. The minimum resistance of the spark channel decreases with an increasing peak current. The results are compared with various theories that attempt to predict the temporal variation of the resistance of spark channels. The comparison shows that further developments in the existing theoretical models are needed in order to reproduce with better accuracy the dynamic behavior of the channel resistance

Marley Becerra

Papers

A simplified physical model to determine the lightning upward connecting leader inception

A self-consistent upward leader propagation model

Time dependent evaluation of the lightning upward connecting leader inception

Gas heating dynamics during leader inception in long air gaps at atmospheric pressure

Resistance of Spark Channels