Lightning Polarity Research Articles

Total lightning signatures in a tornadic thunderstorm over the Pearl River Delta of Southern China

Tornado rises rotating air columns extending from the bottom of cumulonimbus clouds to the ground, often accompanied by strong convection with thunderstorms, hail, and short-term heavy precipitation, which seriously threaten people's lives and property safety. Studying the characteristics of thunderstorm activity during a tornado is crucial for comprehending the atmospheric electrical mechanisms involved in its generation process and developing cooperative methods for tornado warning and forecasting. Based on the VLF/LF total lightning location system and radar echo data, this paper analyzes the spatial-temporal evolution, frequency, polarity, and height of total lightning during a strong tornado (EF3) in the Pearl River Delta region on June 3, 2014. The lightning activity lasted for about 3.5 h, with a total of 41,117 total lightning flashes, of which intra-cloud (IC) flashes accounted for 74.7%, cloud-to-ground (CG) flashes accounted for 21.6%, and narrow bipolar events (NBEs) accounted for 3.7%. Connected-Component Labeling (CCL) algorithm was used to divide the thunderstorm into four stages: initiation, development, maturation, and dissipation, and it was observed that the occurrence of tornadoes was closely related to total lightning activities. The observed characteristics of lightning activity in the tornado are summarized through comparison with other studies.

Understanding the Effects of Aerosols on Electrification and Lightning Polarity in an Idealized Supercell Thunderstorm via Model Emulation

AbstractAerosol effects on the lightning intensity and polarity of a continental supercell storm were investigated using a three‐dimensional lightning scheme within the Weather Research and Forecasting model. We find that both intra‐cloud (IC) and cloud‐to‐ground (CG) flashes are enhanced by the increasing number of cloud condensation nuclei (CCN), especially the percentage of positive CG (+CG) strokes peaking at 42%. Electrical characteristics of the storm varied in different aerosol scenarios through microphysical processes. Added aerosols increase the number of cloud droplets and ice‐phase hydrometeors. The greater ice‐crystal concentration and larger graupel size ensure sufficient charge separation, leading to higher charge density and more lightning discharges. In addition, an inverted polarity charge structure with a strong positive‐charge region in the mid‐levels was formed mainly due to the positively charged graupel in the presence of higher supercooled cloud water content. Positive lightning channels originating from this positive‐charge region propagated to the ground, producing more +CG strokes. When the aerosol concentration was low, the charge density in the upper positive‐charge region was much lower due to smaller ice‐particle content. Consequently, there were barely any +CG strokes. Most of the negative CG flashes deposited positive charge in the lower negative‐charge region.

Estimation of the Number of Sprites Observed over Japan in 5.5 Years Using Lightning Data

This study is based on 5.5 years of continuous observation of sprites from Sagamihara, Japan. Up to February 2022, we detected 537 sprites and found that the most significant number of sprites were observed during the winter (303 sprites); on the other hand, there were only 46 sprites in summer. The hourly distribution of the number of observed sprites peaked at midnight JST (15:00 and 16:00 UTC). To understand the seasonal and the hourly distribution of sprites, we estimate the number of sprites considering the energy and the polarity of lightning, the temporal changes of surrounding environments of sprites, and the conditions for generating sprites. We found that the energy of lightning, the monthly ratio of a positive cloud-to-ground discharge, and the hourly change in the electron number density are essential factors to match the observed sprite distributions.

Dependence of Warm Season Cloud-to-Ground Lightning Polarity on Environmental Conditions over Sichuan, Southwest China

The effects of thermodynamic and moisture factors on cloud-to-ground (CG) lightning polarity in the warm season were discussed. Small convective available potential energy (CAPE) represents relatively shallow convection, which is beneficial to the generation of positive lightning. Large vertical wind shear results in the displacement of upper-level positive ice crystals and promotes the initiation of +CG lightning from positive ice crystals. The dry low- to midlevel troposphere and the high cloud base in the plateau region favor +CG lightning, while the strong thermodynamic conditions in the basin region offset the influence of these moisture factors. In the plateau region, due to the limited cloud thickness, high total column liquid water may mean high cloud water content in the warm cloud region rather than high liquid water content in the mixed-phase region, which is unfavorable for the middle-level positive graupel and thus is unfavorable for the initiation of +CG lightning. In the basin region, the cloud thickness is relatively thicker, the high total column liquid water means that the liquid water content in the warm cloud and the mixed-phase region is both high, which is conducive to the middle-level positive graupel and the +CG lightning.

ВПЛИВ НА НЕЛІНІЙНИЙ ОБМЕЖУВАЧ ПЕРЕНАПРУГ СТРУМІВ БЛИСКАВКИ НЕГАТИВНОЇ ТА ПОЗИТИВНОЇ ПОЛЯРНОСТІ

Purpose. The study of surge arrester models using oscillograms of real lightning currents and taking into account the polarity of lightning has been further developed. Methodology. Methods of circuit simulation for electrical scheme modes, free software for digitizing a bitmap graphic image of a lightning current oscillogram and converting it into an array of points are used. Results. A studying the model of a typical surge arrester with a nominal discharge current of 10 kA, intended for use in a 10 kV network was carried out. A well-known dynamic (frequency-dependent) model proposed by the IEEE working group was used to simulate the surge arrester. Oscillograms of real lightning currents of negative and positive polarity which were recorded on special towers were digitized. Using a free circuit simulation program, the residual voltage at the terminals of the surge arrester was determined and the energy that the surge arrester should absorb in the event that lightning currents of different waveforms and polarities flow through it, but with the same amplitude of 10 kA. It has been found that positive lightning strikes are potentially more dangerous than negative lightning strikes. It was shown that before the ending of the positive lightning current, the surge arrester have to absorb more than ten times more energy than before the ending of the negative lightning current of the same amplitude. Further development of the proposed approach is seen in its use for the tasks of improving the lightning protection of overhead power lines and protecting the high-voltage insulation of electrical equipment of substations from lightning overvoltage. Originality. The approach takes into account the differences between impulses of lightning currents of negative and positive polarity, which cannot be achieved when using the approximation of lightning currents by simplified expressions. Practical value. The use of the proposed approach improves the accuracy and visualization of research, since it takes into account the actual features of the lightning current curve. References 20, figures 12.

Lightning as an asymmetric branching network

The polarity asymmetry in lightning macroscopic behavior is well established for both cloud-to-ground and intracloud flashes. Negative polarity discharges to the ground most often consist of a series of strikes passing through one channel, while positive flashes, as a rule, are limited to one stroke; negative and positive leaders of lightning discharges have significant morphological differences; the growth of positive leaders is accompanied by the development of negative recoil leaders, and positive recoil leaders have never been observed (or do not exist). At present a consistent description of the mechanisms of macro-scale manifestations of the lightning discharge asymmetry causes considerable difficulties. Here we use the hierarchical Horton – Strahler scheme to estimate the structural asymmetry of the lightning discharge tree on the analogy with river systems. We postulate that displacement of the bi-directional leader reversing point (zero charge level of the lightning channel corona sheath) from the place of initiation towards the positive leader development is a fundamental manifestation of the lightning polarity asymmetry. This approach not only has the potential to relate the reversing point displacement rate with the difference in peripheral currents, but also helps uncover the mechanism that provide both the competitive suppression of the positive leader side branches and the negative leader renewal. Our results further indicate that the reversing point displacement determines the lightning principal direction of propagation.Lightning structural asymmetry is estimated using Horton – Strahler numbers Lightning reversing point moves towards the positive leader tip The difference in lightning peripheral currents determines reversing point rate Asymmetry provides competitive suppression of the positive leader side branches.

Relationship between cloud‐to‐ground lightning polarity and the space‐time distribution of solid hydrometeors in isolated summer thunderclouds observed by X‐band polarimetric radar

AbstractTo understand the charge distribution in thunderclouds associated with solid hydrometeors, the relationship between cloud‐to‐ground (CG) lightning polarity and the space‐time distribution of solid hydrometeors for isolated summer thunderclouds in Japan is examined using X‐band polarimetric radar. Hydrometeor classification was conducted to examine the space‐time distribution of dry snow, ice crystal, dry graupel (DG), and wet graupel in thunderclouds. Two thunderstorm cases were selected for analysis: 26 July 2010, which generated few positive CG flashes, and 25 August 2010, which generated positive CG flashes in the reflectivity cores. In both cases, negative CG flashes were observed in all reflectivity cores when a large volume of DG was identified above the height of −10°C level. This is consistent with previous studies showing that graupel particles have a negative charge below temperatures of −10°C. Reflectivity cores with positive CG flashes had a large volume of DG up to high altitudes (around or above the −45°C level). Further, reflectivity cores that sustained large DG volumes at high altitudes had a relatively large number of positive CG flashes. The top height of the DG volume reached lower altitudes for reflectivity cores without positive CG flashes compared with those with positive CG flashes. These results suggest that the persistence of graupel particles in reflectivity cores at high altitudes, implying the existence of strong updraft, is a necessary condition for positive CG flashes in summer thunderclouds. This effect would likely be caused by the positively charged graupel particles under high rime accretion rates.

Environmental Control of Cloud-to-Ground Lightning Polarity in Severe Storms

Abstract In this study, it is hypothesized that the mesoscale environment can indirectly control the cloud-to-ground (CG) lightning polarity of severe storms by directly affecting their structural, dynamical, and microphysical properties, which in turn directly control cloud electrification and ground flash polarity. A more specific hypothesis, which has been supported by past observational and laboratory charging studies, suggests that broad, strong updrafts and associated large liquid water contents in severe storms lead to the generation of an inverted charge structure and enhanced +CG lightning production. The corollary is that environmental conditions favoring these kinematic and microphysical characteristics should support severe storms generating an anomalously high (>25%) percentage of +CG lightning (i.e., positive storms) while environmental conditions relatively less favorable should sustain storms characterized by a typical (≤25%) percentage of +CG lightning (i.e., negative storms). Forty-eight inflow proximity soundings were analyzed to characterize the environment of nine distinct mesoscale regions of severe storms (4 positive and 5 negative) on 6 days during May–June 2002 over the central United States. This analysis clearly demonstrated significant and systematic differences in the mesoscale environments of positive and negative storms, which were consistent with the stated hypothesis. When compared to negative storms, positive storms occurred in environments associated with a drier low to midtroposphere, higher cloud-base height, smaller warm cloud depth, stronger conditional instability, larger 0–3 km AGL wind shear, stronger 0–2 km AGL storm relative wind speed, and larger buoyancy in the mixed-phase zone, at a statistically significant level. Differences in the warm cloud depth of positive and negative storms were by far the most dramatic, suggesting an important role for this parameter in controlling CG lightning polarity. In this study, strong correlations between the mesoscale environment and CG lightning polarity were demonstrated. However, causality could not be verified due to a lack of in situ observations to confirm the hypothesized microphysical, dynamical, and electrical responses to variations in environmental conditions that ultimately determined the dominant CG polarity. Future observational field programs and cloud modeling studies should focus on these critical intermediary processes.

Numerical Simulation of Electrical Space Charge Density and Lightning by using a 3-Dimensional Cloud-Resolving Model

A new lightning formation scheme to simulate electrical space charge density and lightning is introduced into a 3-dimensional cloud-resolving model (JMANHM: Japan Meteorological Agency NonHydrostatic Model, Saito et al. 2006). A tripole structure in the electrical space charge distribution in cumulonimbi, clarified previous observational and numerical idealized studies (e.g., Williams 1989; Takahashi 1984), is well reproduced in numerical simulations with this new scheme.The numerical simulations with the horizontal resolution of 1.5 km are performed to reproduce the thunderstorm observed over the Kanto area, the central part of the Japan Islands, on 08 July 2004. In these simulations, four electrical charge transfer methods are applied to this event. Among them, the modified method from Helsdon and Farley (1987) (mHF-method) predicts cloud-ground lightning polarity most successfully in comparison with the observations. The electrical space charge structures simulated with the mHF-method agree with the previous observational and idealized numerical studies.

The Relationship between Severe Storm Reports and Cloud-to-Ground Lightning Polarity in the Contiguous United States from 1989 to 1998

Abstract The majority (61%) of severe storm reports (i.e., large hail and tornado) during the 1989–98 warm seasons (April–September) were associated with predominantly (>90%) negative cloud-to-ground (PNCG) lightning. Across the contiguous United States, only 15% of severe storm reports were characterized by predominantly (>50%) positive CG (PPCG) lightning activity. However, significant regional variability occurred in the relationship between warm season severe storm reports and CG lightning polarity. In the eastern United States, a significant fraction (81%) of severe storm reports occurred nearby PNCG lightning while only 2% of severe storms were associated with PPCG lightning. The CG lightning behavior was quite different over the northern plains; only 28% of severe storm reports were linked with PNCG lightning while 43% were characterized by PPCG lightning. Although the direct physical relationship is still not evident, this regional variability appears to be at least partially explained by differen...

The Relationship between Cloud-to-Ground Lightning Polarity and Surface Equivalent Potential Temperature during Three Tornadic Outbreaks

Abstract The relationship between cloud-to-ground (CG) lightning polarity and surface equivalent potential temperature (θe) is examined for the 26 April 1991, Andover–Wichita, Kansas; the 13 March 1990, Hesston, Kansas; and the 28 August 1990, Plainfield, Illinois, tornadic storm events. The majority of thunderstorms whose CG lightning activity was dominated by negative flashes (labeled negative storms) formed in regions of weak θe gradient and downstream of a θe maximum. The majority of thunderstorms whose initial CG lightning activity was dominated by positive flashes formed in regions of strong θe gradient, upstream of a θe maximum. Some of these storms moved adjacent to the θe maximum and were dominated by positive CG lightning throughout their lifetimes (labeled “positive storms”). The other initially positive storms moved through the θe maximum where their updrafts appeared to undergo intensification. The storms’ dominant CG polarity switched from positive to negative after they crossed the θe maxim...