The results of the physical modelling of the formation processes of upward discharges from grounded objects in the artificial thunderstorm cell’s electric field are presented. We established the considerable influence of the electrode tip’s radius on the pulse streamer corona stem’s parameters and, subsequently, on the probability of the transformation of the impulse streamer corona first flash’s stem into a first stage of upward leader. We determined the diapason of the optimal tip radii for a lightning rod or lightning conductor, which allows for the most probable formation of the first impulse streamer corona, with the parameters providing the best conditions for the upward leader’s start, the purpose of which is the lowering of the probability of lightning striking the object under protection. A considerable difference between the electrical characteristics of the first impulse corona flash with and without the streamer–leader transition was established. It was shown that the amplitude of the streamer corona flash current impulse is considerable, but not the main defining factor of the streamer–leader transition. It is established that the charge value of the streamer corona first flash is not a threshold requirement for the formation of the upward leader from a ground object, but only defines the probability of the successful upward leader formation. Based on the analysis of the experimental data received, we suggest that there is a dependency between the probability of upward positive leader formation from the grounded objects and the charge value of the first pulse streamer corona flash for the rod (centered) and rope (elongated) lightning conductors and objects in the electric field of the thundercloud and downward lightning leader. The obtained results can be used for mathematical modelling of the formation processes of upward discharges from grounded objects in the artificial thunderstorm’s electric field, as in a natural thunderstorm situation.

https://www.mdpi.com/2073-4433/13/8/1339/pdf?version=1661236749

The Physical Experimental Modelling of the Formation Processes of Upward Discharges from Grounded Objects in the Artificial Thunderstorm Cell’s Electric Field

The article represents results of a physical simulation of incomplete upward leader discharges induced on air transmission lines’ elements, using charged artificial thunderstorm cells of negative polarity. The influence of such discharges on closely located model sensors (both of rod and elongated types) of digital monitoring systems, as well as on the models of receiver-transmission systems of local data collection (antennas), was determined. Effect of heterogeneity of electromagnetic field caused by incomplete upward discharges on frequency specter of signals generated on sensors and antennas was estimated. Wavelet analysis was carried out to determine the basic frequency diapasons of such signals. Based on experimental data obtained, suppositions about the extent of influence of nearby incomplete leader discharges on the functioning of currently used systems of transmission lines’ monitoring were made.

Artificial Negative Polarity Thunderstorm Cell Modeling of Nearby Incomplete Upward Discharges’ Influence on Elements of Monitoring Systems for Air Transmission Lines

The first results of the physical modeling of positive multistrike lightning formation processes using positively charged artificial thunderstorm cells are presented. Experimental studies have shown a significant influence of the number of thunderstorm cells and groups of model hydrometeors introduced into them on the probability of the initiation of repeated strikes. It was found that with an increased number of cells and groups of model hydrometeors, the probability of the formation of repeated positive discharges increases several times. When the second group of model hydrometeors has been introduced into the artificial thunderstorm cell, or when the number of cells has been increased, the probability of the repeated discharge initiation has increased almost in three and in four times respectively. It has been revealed that, depending on the arrangement of model hydrometeor groups in artificial thundercloud cells, the formation of repeated positive discharges from them may proceed both with the “connection” of the uncharged areas of the lower cell and with the “connection” of the upper cell. The parameters of the first and repeated impulse current pulses between the positively charged cells and the ground were determined. It was found that with an increasing number of model hydrometeor groups, the value of the charge neutralized during the stages of first and repeated discharge formation increases. When forming multistrike positive discharges with the “connection” of the upper artificial thunderstorm cell, 20–30% more cloud charge has been neutralized during the repeated discharge than during the formation of a single positive discharge. It was found that the formation of positive repeated discharges was observed in about half of the cases, and that the radiation power and impulse current amplitude at repeated discharges are higher than at the first discharge. This article discusses some possible reasons for such a ratio between the parameters of the first and repeated discharges. It is assumed that the discovered significant influence of large model hydrometeor groups on the probability of the formation and the characteristics of repeated positive discharges from artificial thunderstorm cells indicate a possible key influence of hail arrays in the thundercloud on the formation of repeated strikes of positive lightning and bipolar lightning. The obtained results show that artificial thunderstorm cells of positive polarity, together with groups of large model hydrometeors, have prospects for physical modeling and the investigation of processes of the formation of positive and bipolar repeated lightning strikes.

/pdf/physical-modeling-of-positive-multistrike-lightning-1diuwl3m.pdf

Physical Modeling of Positive Multistrike Lightning Formation

A special experimental setup with a three-electrode discharge gap was used to study the dynamic characteristics of the ultra-high- and super-high-frequency (UHF-SHF) electromagnetic radiation of a high-voltage discharge having the streamer form with reference to the dynamics of individual streamers at the nanosecond time resolution. We performed synchronous detection of the radiation waveforms using a wideband horn antenna, on the one hand, and high-speed photography of the discharge development in the discharge gap using an ICCD camera, on the other hand. It was found that the high-voltage discharge is a source of radiation in the frequency band up to 10 GHz, which is a series of individual ultrawideband (UWB) bursts having durations of less than 1 ns and leading fronts less than 100 ps long and appears when the streamers moving from the discharge anode (thin wire) meet the discharge cathode (plane). By the order of magnitude, the number of radiation bursts corresponds to the number of streamers that reach the electrode, according to the high-speed photography data. The qualitative data confirmed by simple theoretical estimations show that the sources of UWB radiation pulses are individual streamers at the moment of their contact with the electrode, and the radiation of the streamers can be regarded as transition radiation.

/pdf/amplitude-temporal-and-spectral-characteristics-of-pulsed-rw9hde1w.pdf

Amplitude–Temporal and Spectral Characteristics of Pulsed UHF-SHF Radiation of a High-Voltage Streamer Discharge in Air under the Atmospheric Pressure

Spectral Characteristics of Signals Induced by an Artificial Thunderstorm Cell on Dummy Elements of OHPL Monitoring Systems Protected by Dielectric Shells

The results of a physical simulation using negatively charged artificial thunderstorm cells to test the spectrum of possible electromagnetic effects of upward streamer discharges on the model elements of transmission line monitoring systems (sensor or antennas) are presented. Rod and elongated model elements with different electric field amplification coefficients are investigated. A generalization is made about the parameters of upward streamer current impulse and its electromagnetic effect on both kinds of model elements. A wavelet analysis of the upward streamer corona current impulse and of the signal simultaneously induced in the neighboring model element is conducted. A generalization of the spectral characteristics of the upward streamer current and of the signals induced by the electromagnetic radiation of the nearby impulse streamer corona on model elements is made. The reasons for super-high and ultra-high frequency ranges in the wavelet spectrum of the induced electromagnetic effect are discussed. The characteristic spectral ranges of the possible electromagnetic effect of upward streamer flash on the elements of transmission line monitoring systems are considered.

Physical Simulation of the Spectrum of Possible Electromagnetic Effects of Upward Streamer Discharges on Model Elements of Transmission Line Monitoring Systems Using Artificial Thunderstorm Cell

Application of the system of two negatively charged artificial thunderstorm cells with a model hydrometeor array between them could help in the investigation of the problem of the subsequent lightning stroke initiation and propagation inside a thundercloud. The article presents the results of an experimental investigation of the influence of the large model hydrometeor arrays on the possibility of switching of upper negatively charged cell to a discharge channel between the bottom cell and the ground. It also compares the peculiarities of the first and subsequent return stroke formation in the systems “negative artificial cell – negative artificial cell – ground” in cases with and without the model hydrometeor array between the cells. Application of the obtained results to a natural thunderstorm including a possible role of the large hail arrays in the multi stroke lightning formation is discussed.

Investigation of Possible Role of Hydrometeor Arrays on Subsequent Stroke Initiation Using System of Artificial Thunderstorm Cells of Negative Polarity

Application of the system of positively and negatively charged artificial thunderstorm cells with the model hydrometeor array between them could help to clarify the mechanism of the intracloud lightning initiation and its propagation inside a thundercloud. Results of an experimental investigation of the influence of the groups different types of large model hydrometeors of types disposed between differently charged artificial thunderstorm cells and partly inside them on the discharge initiation and propagation between the clouds have been presented. Peculiarities of the discharge formation on the hydrometeor array in the systems "negative artificial cell – positive artificial cell – ground" and "positive artificial cell – negative artificial cell – ground" have been analyzed. Relevance of a received results to the natural thunderstorm and to the methods of the artificial intracloud initiation has been discussed.

Tatiana Kivshar

Papers

Physical Simulation of the Spectrum of Possible Electromagnetic Effects of Upward Streamer Discharges on Model Elements of Transmission Line Monitoring Systems Using Artificial Thunderstorm Cell

Artificial Negative Polarity Thunderstorm Cell Modeling of Nearby Incomplete Upward Discharges’ Influence on Elements of Monitoring Systems for Air Transmission Lines

Investigation of Possible Role of Hydrometeor Arrays on Subsequent Stroke Initiation Using System of Artificial Thunderstorm Cells of Negative Polarity

Influence of Model Hydrometeors on Initiation of Discharge Phenomena between Artificial Thunderstorm Cells of Different Polarity