Lightning Physics

The author presents an exciting new hypothesis for megafauna extinction based upon historical, mythical, geological, astronomic, and atmospheric evidence. While not conclusive, it is highly compelling and demands further investigation. Examples of cross cultural motifs in the form of glyphs, mounds, and earthworks are provided with mythic comparisons and contrasts. Counter arguments are provided throughout as well as strong debunking of prior archaeological biases rooted in Victorian, antiquated pseudoscience. Assumptions in the two models presented for plasma-arc-discharge mechanism are clearly listed, as well as known facts. Citations enable cross reference while the work focuses not on diffusion anthropology, but realistic atmospheric/astronomical plasmoid petroglyph formations recorded in rock

A physics-based model describing the thermal interaction between a lightning channel and a composite structure has been developed. The model includes: (i) spatial and temporal evolution of the lightning channel as a function of the electric current waveform; (ii) temporary and spatially non-uniform heat flux generated at the composite structure, where the heat flux is an explicit function of the electric current waveform and the instant lightning channel radius; (iii) nonlinear transient heat transfer problem formulation for layered anisotropic composites that accounts for temperature-dependent material properties,  a moving boundary of the expanding lightning channel, and phase transition moving boundary associated with instantaneous material removal due to sublimation. The model is applied for evaluation of thermal damage of the tip glass fiber reinforced polymer matrix composite panel of the Sandia 100-meter All-glass Baseline Wind Turbine Blade (SNL 100-00) subjected to lightning strike.

Receptor plays an essential role in determining the efficiency of lightning strike protection on wind turbine blades. To investigate the effects of receptors with different shapes and sizes on the lightning strike protection, we apply five different receptor configurations to the blade of a high fidelity wind turbine model. The static electric field strength on the blade surfaces due to a lightning stepped leader is predicted through the development of a numerical model with finite element analysis. The interception efficiency is evaluated by comparing the predicted maximum electric field strength in the vicinity of the receptors.  In addition, the locations of the predicted lightning strike attachment points match well with those obtained by experimental measurements, which validate the current numerical approach.

In this paper, we investigate the wavelet characteristics of the first electric field pulse of four different flash types namely negative cloud-to-ground flash (-CG), positive cloud-to-ground flash (+CG), cloud flash (IC) and isolated breakdown flash (IB). A total 110 fine waveforms out of 885 were selected which have been recorded during summer between May and August 2010 in Uppsala, Sweden. The measurement was done by using an electric field broadband antenna system with the time resolution of 50 Megasample per second. Evidence from our wavelet analysis suggests that the ionization process during the initial leader development (coincide with the detection of the first electric field pulse) of at least three flashes (-CG, IC, and IB) in Sweden was dictated directly by the existence and magnitude of localized free ions region and lower positive charge center (p region). In general, we found that both single peak and multiple peaks pulses of the negative CG and IC flashes radiated energy at higher frequencies and gain larger bandwidth when compared to positive CG and IB flashes. We suggest that the initial leader development of both IC and negative CG flashes underwent very rapid and much more extensive ionization process when compared to the positive CG and IB flashes. In specific comparison between negative CG and IC flashes, both temporal and wavelet analyses suggest that the first electric field pulses of IC flash radiated energy at higher frequency in both single spread categories and radiated energy at lower frequency in both multiple spread categories when compared to the negative CG flash. This finding may explain the observation of much slower and less bright type  leader (ionization process not so extensive) compared to much faster and very bright type  leader (ionization process very rapid and more extensive). As for positive CG and IB flashes, the single peak pulses of positive CG radiated energy at much higher frequency while the multiple peaks pulses radiated energy at much lower frequency than IB flash. We suggest that the initiation mechanism of positive CG was dictated directly by the background electric field between the main positive charge centre and the ground, which is distinct from the initiation mechanism of IB flash. The presence of small magnitude of localized free ions region facilitated the rapidity of the ionization process in the initial leader development of IB flash.

A primary motivation for this study comes from the need to improve the ability of polymer matrix composites to withstand lightning strikes. In particular, we are concerned with lightning strike damage in composite wind turbine blades. The problem is essentially multiphysic, as the electric-current-induced temperature in the composite blade subjected to a lightning strike may reach up to 1,200 °C, leading to extensive thermal damage including surface damage, delamination, cracks, matrix decomposition, fiber breakage and sublimation, and abrupt failure of the blade.   
In this work, the thermal response of the polymer-matrix composite laminate used in a Sandia 100-meter All-glass Baseline Wind Turbine Blade (SNL 100-00) subjected to lightning strike is studied. The tip region composite panel is considered, as it has been reported in the literature that the blade tip is more susceptible to lightning strike than the remaining parts of the blade.
A physical model to show the surface interaction between the lightning arc and the composite structure has been developed. The model provides time- and electric-current-dependent variation of the lightning arc radius and lightning-current-induced heat flux generated at the composite surface. The temperature-dependent thermal properties of the VectorPly E-LT 5500 unidirectional [0]2 E-glass fiber vinyl ester resin matrix fabric and SNL triaxial [±45]2[0]2 E-glass fiber vinyl ester resin matrix fabric used in the wind blade tip composite panel were derived using available experimental data. The formulated nonlinear transient heat transfer problem with moving boundary is solved using the finite element method. The solution procedure accounts for phase transitions in the materials, and the obtained results include temperature field profiles and evolution of the thermal damage.

Electric radiation fields produced by lightning cloud flashes have been analyzed using Fourier methods to obtain amplitude spectra for frequencies in the range of 20 kHz to 20 MHz. Time to thunder measurements were used to extract the distances to the cloud flashes from the measurement site. The spectra were generated by analyzing the first 10 ms time window of cloud flashes with 10 ns sampling resolution, and they show f-1 frequency dependence up to 2 MHz followed by f-2 dependence and higher for frequencies above 2 MHz. The results agree very well with previous measurements carried out for individual pulses produced by various lightning processes. By utilizing digital filters, it has been shown that measurements taken with narrowband filters agree with the results produced under wideband measurements

In this paper, the electric fields in the wind turbine blades due to the lightning stepped leader are studied and the dielectric breakdown is assessed. The developed finite element analysis (FEA) includes the full length of the leader and enables one to incorporate various uniform and non-uniform charge density models. The lightning striking distance is calculated using the rolling sphere method. The electric field in a horizontal axis wind turbine with three blades representing Sandia 100-meter All-glass Baseline Wind Turbine Blades (SNL 100-00) at three different lightning protection levels (LPL) is computed and compared to the dielectric breakdown strength of the blades. The dielectric breakdown strength of the blades is evaluated based on the experimental data. The results show that the tip region of the blade is the most vulnerable to the dielectric breakdown with the safety factor as low as 1.32 at LPL I.

We report synchronized optical observations of sprites in Israel during the winters of 2006/7–2007/8. Based on several events, we suggest that the elements of columniform sprites are organized in spaced intervals on the circumference of a circle centered directly above, or a little offset, to the vertical direction from the parent lightning. In 2D images most of the cases show columns to be arranged in highly eccentric elliptical forms or in straight rows. The analysis of the optical images provided the geometrical dimensions of the columns and their spatial organization. We used an electrostatic model of the QE field with reasonable assumptions on the location and magnitude of the cloud charge center, constrained by ELF evaluation of the Charge Moment Change in the parent flash, to show that the observed diameter of the columnar arrangement closely matches the conventional breakdown field line contour at the same altitude.

This work is concerned with thermal ablation modeling in carbon fiber-reinforced polymer-matrix composite laminates subjected to the lightnig strike. Both direct heat injection and Joule heating produced by the lightning current are taken into account. First, a model describing interaction of the lightning current channel with a conductive structure is presented. The model includes channel expansion and spatial and temporal distribution of the lightning current and linghtning-induced heat flux. Second, anisotropic electrical and thermal properties of the CFRP composite laminates are determined in a wide temperature range (up to the sublimation temperature of the carbon fibers) using experimental data and micromechanics considerations. Third, a nonlinear thermo-electric coupled problem is formulated and solved for a CFRP composite laminate to determine the electric-current-induced temperature distribution and associated thermal ablation. Finally, the obtained predictions of thermal ablation in the CFRP composite laminate are compared to the reported experimental results. It is found that the predicted thermal ablation depths agree well with those reported in the experimental study.

This paper investigates the existence of distinctive features between 4 different types of lightning discharges, namely negative cloud to ground discharge (-CG), positive cloud to ground discharge (+CG), cloud discharge (IC) and isolated breakdown discharge (IB). A total of 110 very fine structure waveforms of 44 -CG, 16 +CG, 39 IC, and 11 IB discharges have been selected from a collection of 885 waveforms measured using fast electric field broadband antenna system. The measurements were carried out in Uppsala, Sweden from May to August 2010. We found that there are significant distinctions within the first 1 ms among different types of lightning discharges (-CG, +CG, IC, and IB). For example, the pulses in -CG discharges are more frequent than other discharges; the pulses in +CG discharges have the highest intensity and the IC discharge pulses tend to have shorter duration.

Flow distributions in the heart and lung are heterogeneous but not at all random. The apparent degree of heterogeneity increases as one reduces the size of observable elements; the fact that the dispersion of flows shows a logarithmic relation to element size says that the system is statistically fractal. The fractal characterization is a statement that the system is nonrandom and that it shows correlation. The close near neighbor correlation has as the corollary of long tailing or falloff in correlation with distance, so called spatial persistence. Correlation can be expected because flow is delivered via a branching vascular system, and so it appears that the structure of the vasculature itself contributes. Since it is also practical and efficient for growth to occur via recursive rules, such as branch, grow, and repeat the branching and growing, it appears that fractals may be useful in understanding the ontological aspects of growth of tissues and organs, thereby minimizing the requirements for genetic material.

Narrow Bipolar Pulses (NBPs) is a special type of intra-cloud lightning discharge activities and was observed with both polarities: negative (NNBP) and positive (NPBP). It is known with other names also such as Narrow Bipolar Events (NBEs), energetic intracloud events, and Compact Intracloud Discharges (CIDs). NBP signatures have been measured by using various methods such as electric field change recording systems, HF-VHF direct measurement systems (filter-detector receiver), and satellite-based systems. To the best of our knowledge, there are no attempts have been made to measure NBP signatures at microwave region so far. In this paper, observations of microwave radiation from thunderstorms have been made during the northeastern monsoon season of 2012 in Malaysia. Fast electric field change recording and broadband microwave receiver systems have captured simultaneous records of NBPs electric field change and microwave radiation, respectively. Strong noise-like burst of microwave radiation pulses associated with NBP events were detected. The total duration of the microwave bursts of the pulses is in the range between 2 and 8μs for both NNBPs and NPBPs. More than 70% of the recorded radiation bursts arrived a few microseconds before the onset of the corresponding NBPs. The analyzed temporal characteristics of the microwave radiation bursts for both NNBPs and NPBPs are similar and indistinctive. In contrast, the analyzed NNBPs and NPBPs temporal characteristics are distinctive to some extent.

(In English) Indonesia is a tropical country and an archipelago that has two seasons namely dry and rainy. In the rainy season often a lightning phenomenon that can endanger national resources. This condition needs to be minimized by the presence of lightning hazard information. This study aims to determine the lightning hazard information display. Service lightning BMKG information in this article shows that at certain times the lightning spread very evenly in the region of South Sumatra and Java. Service lightning hazard information is very useful to support the protection functions of national resources.

Keywords: lightning, protection, national resources, community welfare

(In Bahasa) Indonesia merupakan negara beriklim tropis dan berbentuk kepulauan yang memiliki dua musim yakni kemarau dan hujan. Pada musim hujan seringkali terjadi fenomena petir yang dapat membahayakan sumber daya nasional. Kondisi ini perlu diminimalisasi dengan adanya informasi bahaya petir. Studi ini bertujuan untuk mengetahui tampilan informasi bahaya petir. Metode yang digunakan dalam penelitian ini adalah kualitatif dengan pendekatan observasi. Layanan informasi petir BMKG pada artikel ini menunjukkan bahwa pada waktu-waktu tertentu sebaran petir sangat merata di wilayah Sumatra bagian Selatan dan Jawa. Layanan informasi bahaya petir ini sangat bermanfaat untuk mendukung fungsi proteksi sumber daya nasional.

Kata kunci: petir, proteksi, sumber daya nasional, kesejahteraan masyarakat