Search Results (5)

Mountaintop towers are highly exposed to self-initiated upward lightning flashes. Accurate estimation of their effective height—the equivalent flat-ground height yielding the same lightning exposure—is essential for reliable exposure assessment, for interpreting and calibrating measurement data at instrumented mountaintop towers, and for comparison with established protection guidelines. This study applies a two-step numerical framework that couples finite-element electrostatic simulations with a leader-inception and propagation model for representative tower–terrain configurations reflecting reference instrumented mountaintop sites in lightning research. For each configuration, the stabilization field, the minimum background electric field enabling continuous upward leader propagation to the cloud base, is determined, from which effective heights are obtained. The simulated results agree with the analytical formulation of Zhou et al. (within ~10%), while simplified or empirical approaches by Shindo, Eriksson, and Pierce exhibit larger deviations, especially for broader mountains. A normalized analysis demonstrates that the tower-to-mountain slenderness ratio (h/a) governs the scaling of effective height, following a power-law dependence with exponent −0.17 (R² = 0.94). This compact relation enables direct estimation of effective height from geometric parameters alone, complementing detailed leader-inception modeling. The findings validate the proposed physics-based framework, quantify the geometric dependence of effective height for mountaintop towers, and provide a foundation for improving lightning-exposure assessments, measurement calibration and design standards for elevated structures. Full article

High-voltage direct current (HVDC) transmission lines are increasing in number and overall length. This means their lightning protection must be of higher importance as well. Probability-modulated attractive space (PMAS) theory is a proven geometry-based method for lightning protection calculations. However, it cannot accurately assess the number and parameters of direct lightning strikes to the phase conductor of HVDC lines, because the effect of pole voltage on lightning attachment cannot be considered. This effect can be taken into account with leader progression models, which feature lightning physics models that can quantify the effect of the electric field around the phase conductor, which can be quite complex compared to geometric models in general. In this paper, a novel method, called the attractive space matrix, is presented to examine the effect of the DC electric field around the conductor on the attractive space. The algorithm is based on the physical background of the self-consistent leader inception and propagation model. The results could lead to improved lightning protection of HVDC lines and reduce the outages caused by direct lightning strikes. Full article

The streamer bursts generated during the initiation and propagation of leaders play an important role in the creation and maintenance of hot discharge channels in air. The most important parameters related to streamer bursts in this respect are the length of the streamer bursts, their lateral extent and the charge associated with them. The lateral extent of the streamer bursts may play a significant role in deciding the path and the tortuosity of the discharge channels of laboratory discharges and lightning. The charges associated with the streamer bursts are needed in understanding the physical processes associated with the streamer-to-leader transition. In this paper, the length, the lateral extension and the charge of the streamer regions generated by grounded conductors when exposed to external electric fields are estimated. This estimation is based on two assumptions: (i) once a streamer is incepted, the streamer head follows the direction of maximum background electric field at the location of the streamer head and (ii) the streamer continues to extend along this direction until the potential drop along the streamer channel matches the potential drop caused by the background electric field between the initial and end points of the streamer channel. The same technique could be used to estimate the streamer bursts generated in laboratory discharges and lightning stepped leaders. It is shown that in estimating the geometry of the streamer region, it is necessary to include the spread of streamers caused by branching. Moreover, the charge associated with the streamer region increases as the frequency of branching increases. The results obtained confirm that the charge in the streamer region can significantly change the potential ahead of the streamer region from the background potential and this has to be taken into account in any study that simulates the initiation and propagation of lightning leaders. Since the streamer bursts of leaders control the direction and speed of the leaders, the technique we have used here could be implemented in lightning leader progression models. Full article

Lightning is one of the major environmental threats to aircraft. The lightning strikes during flying are mostly attributed to aircraft-triggered lightning. The first step toward designing suitable protective measures against lightning is identifying the attachment locations. For this purpose, oversimplified approaches are currently employed, which do not represent the associated discharge phenomena. Therefore, in this work, a suitable model is developed for simulating the inception and propagation of bi-polar leader discharge from the aircraft. Modeling of leader discharges requires field computation around the aircraft, which is carried out employing the Surface Charge Simulation Method (SCSM) combined with sub-modeling, which ensures the best accuracy of field computations near nosecone, wingtips, etc. A DC10 aircraft model is considered for the simulation. Simulations are performed for different pairs of leader inception points on aircraft using the developed model. Subsequently, corresponding ambient fields required for stable bi-polar discharge from aircraft are determined. These values are in the range of measured ambient fields reported in the literature. In summary, the present work has come up with a suitable model for simulating the bi-polar leader inception and propagation from the flying aircraft. Using the same, a detailed quantitative description of the discharge phenomena from the aircraft is provided. Full article

In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer–leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others. Full article