Negative Cloud-to-ground Research Articles

Temporal characteristics of positive cloud-to-ground flashes from tropical thunderstorms

The occurrence of positive cloud-to-ground (CG) lightning flashes proves to be a challenging task when compared to the negative CG flash which common happen in tropical region. This due to the positively charged clouds to reach higher altitudes to enable the transfer of electrical charges to the Earth's surface. With several sensors that deployed in the Malacca region (2.314077°N, 102.318282°E) such as the wide band fast and slow antenna, magnetic field sensors, and the electric field mill (EFM-100). This research study focuses on the temporal characteristics of positive CG lightning activity in the tropical region during September and October 2021. A total of 203 positive cloud-to-ground flashes were meticulously analyzed in the context of 16 thunderstorm events. Key findings highlight the consistent initiation of positive cloud-to-ground flashes through initial breakdown (IB) pulses, followed by the development of stepped leaders and subsequent return strokes. Notably, most positive cloud-to-ground events (72%) were observed as single strokes and the maximum multiplicity recorded being four subsequent return strokes. Furthermore, the analysis focuses into the temporal aspects of these lightning events, revealing average durations for various parameters, including rise-time (6.26 μs), zero-crossing (26.43 μs), pulse duration of the first RS (139.76 μs), and the interval from the first IB to the first return stroke (134.19 ms). Additionally, the recorded data from the Electric Field Mill (EFM) instruments together with Constant Altitude Plan Position Indicator (CAPPI) radar demonstrate a notable correlation. Specifically, the electric field (E-field) values exhibit a discernible increase when positive cloud-to-ground lightning events are detected near the lightning sensor.

Observation of tropical positive cloud-to-ground flashes accompanied by chaotic and regular pulse trains

This study investigates the occurrence of chaotic pulse trains (CPTs) and regular pulse trains (RPTs) in tropical positive cloud-to-ground (CG) lightning flashes. These flashes are categorized into four types based on the initial polarity of the initial breakdown (IB) pulses and their relationship to the first return stroke (RS). A total of 71 positive CG flashes from five thunderstorm events were analyzed. The analysis reveals instances of CPTs and RPTs both before and after the first positive RS, along with the occurrence of mixed polarities in RPTs. Variations in IB pulse polarities and the presence of CPTs and RPTs before the first positive RS were observed, contrasting with previous findings in negative CG flashes. All positive CG flashes have been detected when cloud top height occurrences were between 12 and 18 km. In contrast, for negative CG flashes with CPTs and RPTs the cloud top height occurrences were between 5 and 12 km. It is interesting that CPTs and RPTs can be detected during IB process of positive CG flashes at relatively high altitude in the thundercloud. Perhaps due to low pressure at higher altitudes in the cloud, electrical process associated with CPTs and RPTs are easily discharged before the occurrence first positive return stroke. The altitudes of cloud top heights for the inverse polarity of IB pulses were located between 16 and 18 km. This research enhances the understanding of positive CG lightning initiation process and their relationship with CPTs and RPTs, as well as the occurrence of recoil leaders.

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.

An Investigation on Spatiotemporal Sizes of Specific Types of Lightning Flashes

AbstractThe duration and horizontal extension distance (HED) of intracloud (IC), negative cloud‐to‐ground (NCG), positive cloud‐to‐ground (PCG), and bipolar cloud‐to‐ground (BCG) lightning are analyzed using data from the Oklahoma Lightning Mapping Array and the National Lightning Detection Network. All of these conform to lognormal distributions. BCG lightning has the greatest average spatiotemporal size, owing to its longest‐duration and largest‐spatial‐extension discharge process after the first return stroke (RS). Compared with NCG lightning, PCG lightning tends to include longer‐duration and greater‐spatial‐extension discharge processes before the first RS, making the latter have a larger average spatiotemporal size. IC lightning exhibits the smallest average spatiotemporal size, with a higher concentration of samples in smaller size intervals. Overall, as lightning initiation heights increase, IC and NCG lightning duration tends to increase, while NCG lightning variation is mainly due to discharge processes before the first RS. HED of both types initially increases and then decreases, peaking at ∼7 km. The horizontal extension speed (HES) of IC lightning tends to decrease with increasing initiation height, while for NCG lightning, the HES associated with discharge processes before the first RS shows a clearer decreasing trend at higher levels. The NCG lightning initiated below ∼6 km tends to exhibit similar HED before the first RS and increased HED after the first RS. However, for NCG lightning initiated above ∼6 km, the HED before the first RS is notably greater than the increased HED after the first RS.

Sprite Distribution of Different Polarities From ISUAL Observations With Machine Learning Method

AbstractThe morphological features of sprites are closely related to the polarity of their causative lightning strokes. Using the machine learning method, we develop a model with an accuracy of 93.8% to identify the polarity of sprite‐producing cloud‐to‐ground (CG) lightning strokes for events recorded during the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) mission. Approximately 17% of the sprites are identified to be produced by negative CG lightning strokes. The global distribution of the polarity of sprite‐producing CG lightning strokes suggests that the ratio of sprites produced by negative CG lightning strokes relative to sprites produced by positive ones varies with latitude and sea‐land distribution. Sprites produced by negative CG lightning strokes appear to be generated in the tropical regions below 20° latitude and the oceanic area. Moreover, the proportion of sprites produced by negative CG lightning strokes over Africa and North America are much smaller than that over the rest of the continents and the sea.

Contrast between continental and oceanic thunderstorms in producing red sprites and halos

The observations of transient luminous events from space-borne platform extend our exploration on the mysteries of sprite phenomenology from continental thunderstorms to oceanic thunderstorms. By combining with ground-based measurements of causative strokes for hundreds of red sprites observed by the Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) during 2004–2016, there is a consensus that negative cloud-to-ground (CG) strokes spawned by oceanic thunderstorms are more readily to produce sprites. The existing ground-based observations in both Caribbean Sea and near the coast of South China, mainly due to the contributions from numerous amateurs, are generally consistent with the implications of ISUAL observations. However, the physical mechanisms that might cause the enhancement of negative CG strength in the ocean remain not completely understood. There have been analyses on several cases of oceanic thunderstorms abundant in producing negative sprites. It seems that the production of negative sprites heavily depends on the size of parent thunderstorms, and they are often generated by thunderstorm conditions that are also favorable for gigantic jets.

A Statistical Analysis of Total Lightning Flashes and Peak Current from High-Resolution ENTLN Measurements in South China during 2017

Abstract In this study, the spatiotemporal characteristics of total lightning, including cloud-to-ground (CG) and intracloud (IC), flashes and the peak current of CG flashes are investigated using the observations from the Earth Networks Total Lightning Network (ENTLN) during 2017 over Guangdong Province, China, and its adjacent offshore regions, which are the capital of lightning activity and convective rainfall in China. The ENTLN detects 2 825 558 IC and 569 104 CG flashes, accounting for 83.2% and 16.8% of annual-total lightning flashes, respectively, and they are distributed during 224 lightning days or 3316 lightning hours over the regions. The lightning activity peaks in June (IC) and July (CG) with a diurnal peak at 1500 LST. On average, about 70 lightning days with 20 flashes per kilometer squared per year occur inland, and double that many occur offshore. High lightning days and flash density are found in the central and southwestern mountainous region and the Guangdong–Hong Kong–Macao Greater Bay area, where convective activity is high. An analysis of the CG observations reveals that negative CG (NCG) produce an average of 1.96 strokes, with 5% of them having more than six return strokes. The peak currents of NCG strokes increase with increasing multiplicity. Results also show that the peak current and accumulated value of NCG flashes are the appropriate indicators to characterize the intensity of lightning activity in terms of spatiotemporal variations, especially in the mountainous region. It is concluded that IC observations provide more distinct spatial distribution of lightning activity than CG flashes; and those appropriate indicators should be used to represent the peak current of multistroke NCG flashes.

Characteristics of Lightning Electromagnetic Fields Produced by Antarctica Storms

This paper presents the temporal characteristics of electromagnetic fields produced by cloud-to-ground (CG) lightning flashes associated with Antarctica storms. A total of 51 positive CG (+CG) and 103 negative CG (−CG) flashes have been recorded by a magnetic direction finder (MDF) sensor in King Sejong Station, King George Island. In total, 47 positive and 107 negative return strokes were located, ranges from 32 to 569 km. All CG flashes were detected to occur over the ocean. The return strokes characteristics include the observations of slow front, fast rising, rise time, and pulse duration with geometric mean values of 3.2, 0.53, 3.21, 13.12, and 67.09 µs for +CG flashes, while 3.9, 0.57, 3.72, 20.75, and 69.86 µs for −CG flashes, respectively. Additionally, the average peak currents of +CG and −CG flashes were 4.13 kA and 3.14 kA, respectively. The temporal characteristics of the return strokes of Antarctica storms are comparable to other geographical regions. The smaller peak currents might be due to small magnitude of Antarctica cloud charges when compared to other geographical regions.

Characteristics of electric field waveforms produced by negative return strokes in Colombia and their comparison with other regions

This paper presents the statistical analysis of several parameters associated with the electric field generated by negative cloud-to-ground (CG) lightning flashes recorded in the Bogota savannah (central province of Colombia), including a comparison with other regions. In this way, this is the first study in Colombia where eleven parameters of the electric field and two more related to the electric field derivative are analyzed in detail. From a measuring campaign carried out during the second semester of 2016, 306 negative cloud-to-ground lightning flashes containing the same number of first return strokes (FRS) and 483 subsequent return strokes (SRS) had been analyzed. These return strokes occurred in the range from 3 to 250 km from the measuring station, in such a way that the waveforms analyzed have static components, radiated components or a combination of both. At first, a total of 64.7% of negative CG flashes were categorized as multiple-stroke flashes, the average multiplicity was 2.6 strokes/flash and the maximum value reported was 13 strokes. For the first and subsequent return strokes analyzed in Colombia, the arithmetic mean (AM) of the initial electric field peak normalized to 100 km (EP_N) were 27.6 V/m and 12.4 V/m, respectively. On the other hand, the average of the peak value of the electric field derivative (dE/dt)P was 5.9 V/m/μs for FRS and 3.6 V/m/μs for SRS. These results are similar to those observed in Florida, Germany, Sweden, Japan, Sri Lanka and Malaysia, where the EP_N and the (dE/dt)P for FRS are larger than those for SRS. Furthermore, as reported in Malaysia and other tropical regions, several electric field parameters in Colombia are affected by the geographical location, the distance with respect to the measuring system and the propagation medium. The above was more evident for some temporal parameters such as zero-to-peak rise time, the 10–90% transition duration, the slow front duration and the fast front duration. After comparing with previous data related to natural and rocket-triggered lightnings measured in different regions (tropical, subtropical and temperate latitudes), additional differences were also observed.

Statistical analysis of negative cloud-to-ground lightning characteristics in Bogota, Colombia based on electric field measurements

This paper studies the electric field parameters of negative cloud-to-ground (CG) lightning flashes in the Bogota savanna (a large plateau located in central Colombia), and its comparison with other regions. This work is the first of its kind in the country where the parameters of lightning-generated electric fields are analyzed in detail. A total of 329 CG lightning flashes had been examined. These flashes were recorded within 4–250 km from the measuring station during the period August–November 2016. From observations, negative CG flashes comprised 93% of total events registered. It has been found that negative lightning discharges occurred along the plateau (4250 km2 at 2550 m altitude) exhibit some different characteristics compared with measurements carried out in several regions (tropical, subtropical and temperate latitudes). In this study, it was found that 64.7% of the negative CG flashes are multiple strokes with an average multiplicity of 2.58 strokes per flash. In addition, the mean interval between 789 negative return strokes (306 first- and 483 subsequent strokes) was 61.3 ± 51.9 ms, while the arithmetic mean of the total duration for 198 multiple-stroke flashes was 149.5 ms. Other lightning flash features such as relation between the interstroke interval and the return stroke order, the ratio of the subsequent stroke peak field to the corresponding first one and the maximum multiplicity are also analyzed.

The Strongest Negative Lightning Strokes in Winter Thunderstorms in Japan

AbstractWinter thunderstorms in Japan are well known for the frequent production of energetic positive cloud‐to‐ground (CG) lightning flashes. By contrast, strong negative CG flashes or negative return strokes in winter thunderstorms are largely unknown. In this study, we demonstrate that negative return strokes with peak currents larger than 150 kA (absolute value) in winter thunderstorms in Japan mostly produce electric field change waveforms that are different from those of normal return strokes. Due to their unusual waveforms, these strongest negative strokes have not been recognized as return strokes by the lightning research community. We further demonstrate that these strong negative return strokes are preceded by a fast downward negative leader with a short duration and strong peak current. We suggest that the fast and powerful downward negative leader may be associated with downward terrestrial gamma‐ray flashes. We also present evidence that these strong negative strokes are likely “superbolts” observed from space.

Inferring the Severity of a Multicell Thunderstorm Evolving to Supercell, by Means of Radar and Total Lightning

This study analyzes a long-lived thunderstorm with supercell characteristics that took place in the northeastern Iberian Peninsula on 5 July 2012. Severe weather features identified in Doppler radar and total lightning data have been used to infer the severity of this large-hail-bearing storm that substantially damaged local agriculture. Key elements identified in the radar product analysis were: relatively short development time, a long mature phase lasting >2 h, and high and sustained values for most of the radar parameters (reflectivity, vertically integrated liquid, echo tops), which showed an evolution from multicell to supercell structure. Nevertheless, the most significant patterns were the vertical lifting of the cell core, the three-body scatter spike, the bounded weak-echo region, and the anticyclonic rotation, observed in the Doppler velocity fields. Key features identified in the lightning analysis were: 1) the total lightning “jump” as an early sign for severity, 2) the low negative cloud-to-ground (CG) flash rate and 3) the low intensities in negative CG strokes and the regular rate of positive CG as indicators of complexity in the electrical structure. Finally, data strongly suggest the worst damage occurred when the thunderstorm was in its supercell stage. This case study presents one of the first documented supercells in the region.

Characteristics of Negative Cloud‐To‐Ground Flashes Observed in the Brazilian Amazon Region

AbstractFeatures of negative cloud‐to‐ground (CG) flashes in the eastern Amazon region of Brazil, near the equator line, were analyzed from their wideband (160 Hz–10 MHz) electric field records acquired at the UFPA‐Lightning Research Laboratory in Belem, Para, Brazil in the rainy season of 2020. Records of CG flashes were synchronized in time with the Geostationary Lightning Mapper (GLM) data. We found that the GLM relative detection efficiency for negative CG flashes in the region of study is 78.5%. For a subset of 613 flashes that were detected by the GLM, we segregate the events into three categories (close‐, intermediate‐ and distant‐range) according to the GLM reported locations. Flash multiplicity, interstroke time interval, flash duration, leader duration, preliminary‐breakdown (PB) pulse train duration, PB to first return‐stroke (RS) time interval, and the ratio of PB to first RS are determined for 781 negative CG flashes containing 2,383 strokes. The results were compared with previous results obtained in different parts of the globe with an emphasis on studies performed in similar regions such as in the tropics. For all flashes, the average number of strokes per flash is 3.1 and the percentage of single‐stroke flash is 30%. The geometric mean of interstroke intervals, flash duration, PB to first RS time interval, and PB pulse train duration are 63, 186, 10, and 1.5 ms, respectively.

Enhancement of Cloud-to-Ground Lightning Activity Caused by the Urban Effect: A Case Study in the Beijing Metropolitan Area

To investigate the possible impact of urban development on lightning activity, an eight-year (2010–2017) cloud-to-ground (CG) lightning dataset provided by the National-Wide Lightning Detection Network in China was analyzed to characterize the CG lightning activity in the metropolitan area of Beijing. There is a high CG flash density area over the downtown of Beijing, but different from previous studies, the downwind area of Beijing is not significantly enhanced. Compared with the upwind area, the CG flash density in the downtown area was enhanced by about 50%. Negative CG flashes mainly occurred in the downtown and industrial area, while positive CG flashes were distributed evenly. The percentage of positive CG flashes with Ipeak ≥ 75 kA is more than six times that of the corresponding negative CG flashes in the Beijing area. The enhancement of lightning activity varies with season and time. About 98% of CG flashes occurred from May to September, and the peak of CG diurnal variation is from 1900 to 2100 local time. Based on the analysis of thunderstorm types in Beijing, it is considered that the abnormal lightning activity is mainly responsible for an enhancement of the discharge number in frontal systems rather than the increase of the number of local thunderstorms. In addition, there is a non-linear relationship between pollutant concentrations and CG flash number, which indicates that there are other critical factors affecting the production of lightning.

Estimation of the IC to CG Ratio Using JEM‐GLIMS and Ground‐Based Lightning Network Data

AbstractThe occurrence ratio of intracloud (IC) to cloud‐to‐ground (CG) discharges, which is denoted by Z‐ratio, is the crucial parameter for the studies on the global electric circuit. However, the latitudinal and regional dependences of Z‐ratio are not fully clarified. Therefore, using optical data obtained by the Global Lightning and Sprite Measurements on Japanese Experiment Module (JEM‐GLIMS), we distinguished the lightning discharge type, that is, IC, positive CG (+CG), and negative CG (−CG) discharges, and statistically estimated the Z‐ratio. We analyzed 8,354 lightning events that obtained by JEM‐GLIMS observation and succeeded in identifying 4,431 IC discharges, 597 +CG discharges, and 3,326 −CG discharges. From this result, we calculated the Z‐ratio over many regions around the world and estimated its latitudinal and regional dependences. It is found that the Z‐ratio over the continental area is larger than the oceanic area. We also found that the Z‐ratio significantly decreases with the latitude, which is generally comparable to the results shown in the previous studies. The estimated Z‐ratio varies from 2.9–0.29 from the equator to 50° latitude, and the global mean value is 1.6. The regional dependence of Z‐ratio derived from this study can be combined with the CG lightning data provided by the ground‐based lightning detection networks to estimate the occurrence number of IC discharges. Then, the occurrence number of both IC and CG discharges can be used for calculating a more accurate estimation of the total lightning currents in the global electric circuit.

Observations of single-stroke flashes from five isolated small thunderstorms in East China

This paper presents the ground truth datasets of negative cloud-to-ground (NCG) flashes with one single stroke in five isolated small thunderstorms. By developing a machine-learning method based on the convolutional neural network, we identify the return strokes during the whole life of thunderstorms with the wideband electric field waveform of lightning discharges detected by Jianghuai Area Sferic Array. The distribution of flash multiplicity in these thunderstorms exhibits an exponential decrease pattern. The single-stroke flashes (with multiplicity = 1) account for more than 30% of all NCG flashes on a thunderstorm basis, and the proportion of single-stroke flashes tended to be most abundant. When observed at a 20-min interval, the percentage of single-stroke flashes tends to change dramatically during thunderstorm developments, which seems to show an opposite trend with time to the maximum flash multiplicity. Single-stroke flashes tended to be associated with a weaker peak current of initial stroke compared to that of multiple-stroke flashes. It is inferred that the horizontal scale of negative charge regions in thunderclouds might play an important role in enhancing the flash multiplicity.

Seasonal Variability of Lightning Activity in Yakutia in 2009–2019

The instrumental continuous monitoring of lightning activity in Yakutia has been carried by the lightning direction finder since the 2000s. Devices for detection of sferic (very low frequency radio pulses emitted by lightning discharges) in Yakutia were supplemented in 2009 with relatively short-range (effective detection radius up to 480 km) single-point Stormtracker and LD-250 direction finders from Boltek Corporation (Welland, ON, Canada). The Stormtracker gives a slightly overestimated ratio of CG strokes due to the amplitude threshold of a single-point direction finder, but the device has not changed over the years, which allows for the consideration of the annual dynamics of parameters. In 2009, a sensor in Yakutsk was included in the World Wide Lightning Location Network (WWLLN). The seasonal and diurnal variations of the total lightning stroke number in the central part and the entire area of Yakutia were obtained (up to 1200 km in radius and limited by latitude–longitude boundaries of 105–150° E, 55–75° N). The longest thunderstorm seasons are often observed in the southern part of Yakutia. There was a slight increase in the duration of the thunderstorm season until 2015 in the central part of Yakutia. The interannual variations in the total number of lightning strokes showed periodic fluctuations (with a period of about three years) over the whole area of Yakutia. The periods of high lightning activity shifted within a season from year to year, as revealed by the monthly stroke number variation. Thus, the maximum lightning rate occurred at the beginning of summer, in the middle or at the beginning of August, and had a period of about three years. Every summer, there were 2–3 periods of high lightning activity, resulting from the moving average with a two-week window (according to the longest duration of cyclones). If the periods of high lightning activity shifted toward the beginning of summer, a decrease in the number of days between seasonal peaks was observed. If the maximum shifted to the beginning of August, the number of days between peaks increased. The ratio of cloud-to-ground (CG) lightning strokes and the ratio of negative CG strokes was slightly decreasing by 2015 in the central part of Yakutia.

Subseasonal and Diurnal Variability in Lightning and Storm Activity over the Yangtze River Delta, China, during Mei-yu Season

AbstractUsing 5 years of operational Doppler radar, cloud-to-ground (CG) lightning observations, and National Centers for Environmental Prediction reanalysis data, this study examined the spatial and temporal characteristics of and correlations between summer storm and lightning activity over the Yangtze River Delta (YRD), with a focus on subseasonal variability and diurnal cycles. The spatiotemporal features of storm top, duration, maximum reflectivity, size, and cell-based vertical integrated liquid water were investigated using the Storm Cell Identification and Tracking algorithm. Our results revealed that there was high storm activity over the YRD, with weak diurnal variations during the mei-yu period. Specifically, storms were strongly associated with mei-yu fronts and exhibited a moderate size, duration, and intensity. On average, afternoon storms exhibited stronger reflectivity and higher storm tops than morning storms, as evidenced by the afternoon peak in CG lightning. The storm intensity strengthened in the post-mei-yu period, due to an increase in atmospheric instability; this was accompanied by a higher frequency of CG lighting. The diurnal cycles of storm frequency and CG lightning in the post-mei-yu period followed a unimodal pattern with an afternoon peak. This is attributable to increased thermodynamic instability in the afternoon, as little diurnal variation was observed for wind shear and moisture. An inverse correlation between lightning occurrence and mean peak current (MPC) for negative CG lightning was evident during the pre-mei-yu and mei-yu periods. The diurnal variation in MPC for negative CG lightning agreed well with that for storm intensity.

Evolution of the Charge Structure and Lightning Discharge Characteristics of a Qinghai‐Tibet Plateau Thunderstorm Dominated by Negative Cloud‐to‐Ground Flashes

AbstractThe correlation between the charge structure evolution and lightning type and frequency for a multicell thunderstorm dominated by negative cloud‐to‐ground (CG) flash on the Qinghai‐Tibet Plateau was analyzed using observations from a three‐dimensional lightning very high frequency radiation source location system. The analysis results showed the following. (1) In the initial developing stage of the thunderstorm, each cell developed independently and presented an inverted dipole charge structure. As the thunderstorm developed into its mature stage, multiple cells merged, and the charge structure changed to a tripole structure. In the dissipation stage of each thunderstorm region, the charge structure reverted to an inverted dipole or a normal dipole. (2) When the extent of the charge region expanded, the upper and lower charge regions became uneven and asymmetric. (3) In the inverted dipole charge structure, negative CG flashes accounted for 77.2% of the total number of lightning flashes, whereas negative intracloud flashes accounted for only 22.8%. In the tripole charge structure, negative CG flashes, positive intracloud flashes, and negative intracloud flashes accounted for 62%, 21%, and 16%, respectively, of all lightning flashes. These results indicate that the middle negative charge region was the strongest layer of the thunderstorm, while the upper positive charge region was slightly stronger, and the lower positive charge region was the weakest. These findings also indicate that the relative intensity of the charge layers directly determined the lightning quantity and frequency.

Studying Sequences of Initial Breakdown Pulses in Cloud‐to‐Ground Lightning Flashes

AbstractThe properties of the first 5–12 classic initial breakdown pulses (IBPs) of three cloud‐to‐ground (CG) lightning flashes were determined using a modified transmission line model. As part of the modeling, the current with respect to time of each IBP was determined from the measured electric field changes at multiple sites using three theoretical methods called Hilbert transform, Hertzian dipole, and matrix inversion. In the transmission line modeling the length of each IBP was estimated from high‐speed video data of the IBPs. The modeling provided the following properties of the larger classic IBPs in each flash: peak current, velocity, total charge, charge moment, radiated power, and total energy dissipated for successive IB pulses in three developing lightning flashes. For the main initial leader channel in the three CG flashes (and for one long branch), IBP peak current was largest for the first or second classic IBP and declined mostly monotonically with successive IBPs. For the same channels, IBP current velocity was smallest for the first classic IBP and increased mostly monotonically with successive IBPs. The smallest velocities were (2.0, 2.5, 2.5, 3.0) × 107 m/s, respectively, while the largest velocities were (9.2, 12.2, 11.5, 12.0) × 107 m/s, respectively. These data support earlier hypotheses that it is the classic IB pulses during initial leader of normal negative CG flashes that change the nonconductive air into an ionized path that is sufficiently long and conductive to start the stepped leader.