Continuing Current Research Articles

Initiation of Downward Positive Leader Beneath the Negative Leader Channel

AbstractDue to the weak radiation generated by positive leaders, our understanding of how positive leaders are initiated and reach the ground remains limited. This study investigated positive cloud‐to‐ground (CG) lightning induced after the long intracloud lightning based on high‐speed video and fast antenna mapping results. Below the cloud base in the field of view, re‐breakdowns of decayed negative branches occurred consecutively beneath the horizontal negative channel in the form of bidirectional leaders. These bidirectional leaders advanced along the same channel, and eventually, the third reached the ground, generating a positive return stroke (RS) with a peak current of 157 kA. Following the RS, new negative discharges emerge adjacent to the vertical return stroke channel, persisting and propagating to form a continuing current (CC) lasting over 200 milliseconds.

On the Role of Continuing Currents in Lightning‐Induced Fire Ignition

AbstractLightning flashes are an important source of wildfires worldwide, contributing to the emission of trace gases to the atmosphere. Based on experiments and field observations, continuing currents in lightning have since a long time been proposed to play a significant role in the ignition of wildfires. However, simultaneous detections of optical and radio signals from fire‐igniting lightning confirming the role of continuing currents in igniting wildfires are rare. In this work, we first analyze the optical signal of the lightning‐ignited wildfires reported by the Geostationary Lightning Mapper over the Contiguous United States (CONUS) during the summer of 2018, and we then analyze the optical and the Extremely Low Frequency signal of a confirmed fire‐igniting lightning flash in the Swiss Alps. Despite data uncertainties, we found that the probability of ignition of a lightning flash with Continuing Current (CC) lasting more than 10 ms is higher than that of cloud‐to‐ground lightning in CONUS. Finally, we confirm the existence of a long CC (lasting about 400 ms) associated with a long‐lasting optical signal (lasting between 2 and 4 s) of a video‐recorded fire‐igniting lightning flash.

Characteristics of Continuing Current Waveforms and M‐Component Parameters in Triggered Lightning

AbstractBased on directly measured triggered lightning currents, the characteristics of 70 continuing current (CC) waveforms and 106 M‐component waveforms were analyzed. The durations of CC without M‐component are all less than 10 ms, which are significantly less than those of CCs with M‐components. The first M‐component always appears at no more than 4 ms after the return stroke. The characteristics of the superimposed M‐components will be different for CC of different durations. The M‐components superimposed on CCs with duration greater than 10 ms are 3–4 times larger in terms of risetime, half‐peak width, duration, and transfer charge than that superimposed on CCs with duration less than 10 ms. The time difference (TD) between the peak electric field and the peak current of the M‐component is affected by both the continuing current level (ICC) and the magnitude of the M‐component (IM). TD and ICC (or IM) will not be large at the same time. The duration of a CC following a return stroke with a peak current greater than 21.2 kA will not exceed 46.0 ms.

On the processes leading to different modes of charge transfer in negative flashes according to fast videos and correlated records of current and electric field

This work discusses the processes involved in different modes of charge transfer in negative lightning flashes, taking as reference video-records obtained with a fast camera and records of current and close electric-field measured at Morro do Cachimbo Station. The data of two downward and one upward negative flashes are explored for considering the features of these processes and for supporting their interpretation, based on the bidirectional and bipolar leader approach. The processes comprise three sequences (stepped leader - first return stroke, dart leader - subsequent return stroke, dart-stepped leader - subsequent return stroke), in addition to the initial continuous current in upward lightning, return strokes following it, continuing current and M-components, the latter observed superimposed on both the continuing current and the tail of return stroke currents. An unreported process of charge transfer, consisting of the reignition of the dissipating leader of an upward lightning from the ground to the cloud is analyzed as well.

Simultaneous Upward Lightning From Small Structures and From the 150 m High Peissenberg Tower, Germany

In this study, we analyze a lightning event, which occurred on March 20, 2020 at 8:05 pm. Three other-triggered upward lightning developed simultaneously from the 150 m high Peissenberg Tower and from two small structures, a 35 m high mast and a 25 m high Church Tower. The velocity of the upward leaders ranged from 2.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> to 4.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> m/s. In addition, to these upward leaders, the total of 51 isolated leaders were observed. These leaders had no contact to the lightning channel or to other leaders or to objects at ground, i.e., most of them did not develop along a path of the decayed channel of a previous leader. Therefore, it is doubtful whether the isolated leaders may be recoil leaders. The lightning to the Peissenberg Tower was a bipolar flash with a current, which contained several (unusual) positive and negative components. The first component was a negative initial continuous current (ICC), followed by a strong negative current component, with a maximum of 4.1 kA and a duration of 40.2 ms. This current component was superimposed by a pulse train of 26 extremely strong current pulses with peak values up to 1.87 kA. The negative current component was followed by a positive current pulse with a peak value of 31 kA, a 10%–90% risetime of 1.80 ms, an action integral of 0.68 MJ/Ω, a full width on half maximum of 0.67 ms and a duration of 15.7 ms. The positive current pulse was superimposed by strong oscillations with the frequency of about 5 kHz and with amplitudes up to 10.2 kA. After its cessation, the positive current pulse turned into a negative continuing current with the duration of 217 ms, the maximum of 245 A, and the transferred charge of 18.0 C. The negative continuing current was followed by a negative return stroke which in turn was followed by a positive continuing current, which lasted 19.7 ms and had a maximum of 173 A. Finally, a second negative return stroke occurred, which was followed by a short negative continuing current with an M-component.

Characteristics of Impulsive Currents Superimposing on Continuous/Continuing Current of Rocket-Triggered Lightning

Characteristics and mechanism of initial continuous current (ICC) pulses and M components in rocket-triggered lightning were investigated in detailed. The geometric mean current peak, risetime from 10% to 90% peak, half-peak width, and charge transfer of M components were 400 A, 207 μs, 267 μs, and 0.19 C, respectively, exhibiting more pronounced impulsive feature than ICC pulses of which the counterpart parameters were 190 A, 462 μs, 845 μs, and 0.27 C, respectively. A shorter time interval between the prior return stroke (RS) and the following M component (TRS-M) facilitated a stronger M component having larger peak while shorter pulsewidth. In two cases with extremely long lasting ICC and continuing current (CC), 20 Initial continuous current pulses occurred during a 715.3-ms duration and 15 M components occurred during a 218-ms duration. The multiple occurrences of current surges serve to keep the grounding channel active and extend the channel network inside the cloud, and hence prolong the ICC/CC duration. This situation reduced the possibility of RSs thereafter. In addition to the two traditional types of in-cloud discharges that result in M component, we recognized a new scenario that involves a short-term interruption of the upward RS wave and a reactivated breakdown promoted by the residual charge inside the main channel.

Performance of the European Lightning Detection Network EUCLID in Case of Various Types of Current Pulses From Upward Lightning Measured at the Peissenberg Tower

In this paper, we present current pulses from upward lightning, which have been measured since 2011 at the new top structure of the Peissenberg Tower, Germany. The study comprises 38 negative and two positive flashes, which contained 199 current pulses. About 49 of them were return stroke current pulses, 133 of them were current pulses, which superimposed the initial continuous current (ICC-pulses), and 17 of them were M-component current pulses, which superimposed the continuing current of a preceding return stroke. The current pulses are used to evaluate the performance of the European lightning location system EUCLID. Fifty one (25.6%) out of the 199 current pulses were detected by EUCLID, 40 (81.6%) return stroke current pulses, and 11 (8.5%) ICC-pulses or M-component current pulses. The peak currents ranged from 0.1 to 40.8 kA. Two groups of current pulses could be identified. The first group is related to branches of nearby downward lightning which got in contact with the tower. Therefore, EUCLID reported much higher peak currents (more than 100%) compared to the peak currents measured at the Peissenberg Tower. The first group comprises the total of nine current pulses (six ICC-pulses, three return stroke current pulses). The second group of current pulses is related to upward lightning initiated from the top of the tower. The peak current inferred from EUCLID deviates much less from peak current measured at the Peissenberg Tower. The peak current was overestimated by about 20% by EUCLID. The second group comprises the total of 42 current pulses (4 ICC-pulses, 1 M-component current pulses, and 37 return stroke current pulses). The peak currents ranged from 3.1 to 40.8 kA, the geometric mean (GM) was 9.4 kA. About 30% of these events were misclassified as intra-cloud pulses by EUCLID. The GM of the location error was 161 m for all events, and 132 m considering only the return stroke current pulses.

Properties of Three Types of M-Components and ICC-Pulses From Currents of Negative Upward Lightning Measured at the Peissenberg Tower

Channel base currents from natural lightning have been measured on the new top structure of the Peissenberg Tower, Germany, since 2008. Here, an analysis is given of the impulsive currents, called initial continuous current (ICC)-pulses, that occurred during the ICC, and of the impulsive currents, called M-component currents, that occurred during the continuing current following return strokes. It was found that the M-component currents and the ICC-pulses closely resemble each other. The 45 flashes analyzed were exclusively negative upward lightning containing 60 return strokes and 264 impulsive currents (79 M-components and 185 ICC-pulses). A total of 246 (93.2%) impulsive currents were negative ones, and 18 (6.8%) impulsive currents were positive ones. The majority of 83.7% were pure impulsive currents and the minority of 16.3% were combined impulsive currents composed by two or more pure impulsive currents. For the pure impulsive currents, the analysis revealed three different types of waveforms for both the M-component currents and the ICC-pulses. The currents of the first type have a more or less symmetrical wave shape. For the 27 M-component currents and the 103 ICC-pulses (values in parentheses) of the first type, the geometric mean values are 0.7 (0.5) kA for the peak value, 23.9 (24.7) μs for the 10%-to-90% risetime, 101.0 (96.5) μs for the full width at half-maximum (FWHM), and 94.3 (57.1) mC for the transferred charge. The impulsive currents of the second type have a bipolar wave shape with current reversal. For the 31 M-component currents and the 37 ICC-pulses of the second type, the geometric mean values are 0.9 (0.6) kA for the peak value, 11.8 (16.9) μs for the 10%-to-90% risetime, 60.6 (74.7) μs for the FWHM, and −42.4/58.5 (−34.1/26.5) mC for the negative/positive charge of the bipolar pulses. The impulsive currents of the third type have a wave shape, which exhibits a fast rise to peak and a much longer decay to low current values. For the 5 M-component currents and the 18 ICC-pulses of the third type, the geometric mean values are 1.0 (1.2) kA for the current peak, 1.2 (2.9) μs for the 10%-to-90% risetime, 56.8 (29.0) μs for the FWHM, and 44.8 (24.03) mC for the transferred charge.

Observation Results and Discussion on an Upward Leader Followed by a Long Continuing Current After a Return Stroke

AbstractAn abnormal discharge process after a return stroke (RS) in a negative cloud‐to‐ground flash was studied in detail. Correlating high‐speed video images and electric field data, it was found that the abnormal discharge process was initiated at ground and transported positive charge from ground toward cloud. Moreover, there was a long continuing current (CC) initiated by the abnormal upward discharge process. Compared with the characteristics of RSs, CCs and M components, we conclude that the upward discharge process is a kind of upward positive leader. The 3‐D speeds of the positive leader range from 3.72 × 106 m/s to 14.48 × 106 m/s with average value of 6.5 × 106 m/s. As far as we know, it is the first report that a long CC follows the upward positive leader after RS, which is obviously different from traditional CCs. The discovery is helpful to gain a deeper understanding of the mechanism and physical process of negative cloud‐to‐ground flashes.

Measurement of continuing charge transfer in rocket-triggered lightning with low-frequency magnetic sensor at close range

Based on the magnetic fields recorded with a compact low-frequency (LF) magnetic sensor deployed at 78 m distance from the channel base, we reconstruct the time-resolved current waveform for the continuously discharging processes in classical rocket-and-wire triggered lightning flashes, including the initial continuous current (ICC) and long continuing current. Both the overall feature and the millisecond-scale slow variations (e.g., initial current variation, ICC pulses and M-components) embedded in the channel-base current as measured with the conventional methods (such as the shunt or Pearson coil) can be retrieved through the numerical integral of close LF magnetic signals. Despite the artifact caused by the magnetic fields radiated by the fast in-cloud processes, the new approach has the advantage of significantly reduced noise in comparison with the measurements of conventional methods, and it is likely applicable to remotely measure the initial continuous current in upward lightning from high objects and altitude-triggered lightning, as well as long continuing current in natural cloud-to-ground (CG) lightning strokes that occur at sufficiently close range (e.g., within 100 m).

Characteristics and correlation of return stroke, M component and continuing current for triggered lightning

Based on the channel-base current acquired from Guangdong Comprehensive Observation Experiment on Lightning Discharge (GCOELD), the characteristics and correlation of return stroke (RS), M component and continuing current (CC) were analyzed. As for RS, the geometric average values of peak current (PI), half-peak-width (HPW), rise time (t10–90%) and charge transfer within 1ms after the beginning of the RS (Q1ms) are 16.41kA, 17.03μs, 0.43μs and 1.62C, respectively. As for M component, the geometric average values of PI, duration, t10–90%, HPW and charge transfer from the beginning to the end (Q) are 185.75A, 1.68ms, 0.42ms, 0.70ms and 0.11C, respectively. As for CC, the duration, average current and charge transfer are 19.01ms, 202.58A and 3.85C. 66% RSs in triggered lightning are followed by CC processes. And the percentages of long CC (duration≥40ms), short CC (10ms<duration<40ms) and “questionable” CC (duration≤10ms) are 34%, 27%, 39%, respectively. Also, the effects of RS and M component on CC duration have been investigated. An interesting phenomenon of “restricted zone” which indicates that M components with small mean amplitude (<0.5kA) is a necessary factor for the existence of long CC, has been found. It is possible that there are two types of M components which can exert different effect on CC duration. In addtion, we also found three “restricted zone” phenomena which exist in the correlation between peak current, charge transfer, action integral of RS and CC duration. The phenomena indicate that the peak current, transferred charge in 1ms and action integral of RS are inherently correlative to CC duration. Especially for action integral of RS, it plays a more key role in the duration of CC. If the value of action integral is larger than 6300A2s, the long CC is highly unlikely to occur.

Correlation between the channel‐bottom light intensity and channel‐base current of a rocket‐triggered lightning flash

AbstractThe correlations between channel‐bottom light intensity and channel‐base current of all discharge processes of a rocket‐and‐wire‐triggered lightning flash, including initial continuous current (ICC) pulses, ICC pulse background continuing current (IBCC), return strokes, M components, and M component background continuing currents (MBCC), have been investigated. A rough linear correlation has been found between the current squared and the light intensity for ICC pulses (including peaks of different ICC pulses), IBCC, the initial rising stage (IRS) of return strokes (including current peaks of different strokes), and MBCC. The slopes of the correlation regression lines for the current squared versus light intensity of ICC pulses and IBCC are similar, but they are about 2–3 times smaller than the slopes of MBCC and 5–7 times smaller than the slopes of the IRS of return strokes. In contrast, a rough linear correlation has been found between the current and the light intensity for the later slow decay stage of return strokes and for the M components. The slopes of the correlation regression lines of the current versus the light intensity for these latter two processes are found to be similar. No simple correlation has been found between the current and the light intensity for the initial fast decay stage (IFDS) of return strokes. The duration of the IFDS of return strokes generally lasts from several microseconds to several tens of microseconds and is more or less directly proportional to the corresponding peak return stroke current squared. A time delay ranging from 12 µs to 300 µs has been found between the current and the light intensity of all ICC pulses and M components. The time delay decreases as the corresponding peak current increases.

On the relationship between continuing current and positive leader growth

AbstractIt has long been speculated that the source of continuing current (CC) for a negative cloud‐to‐ground flash is provided by the growth of its positive leader into negative charge regions. In this study, data from the Langmuir Electric Field Array (LEFA) and Lightning Mapping Array (LMA) are used to investigate these speculations. LEFA and LMA data provide a way to estimate the occurrence and duration of CC and channel growth throughout a flash, respectively. By connecting LMA VHF sources onto contiguous channels, the growth of the positive leader associated with each return stroke is inferred. A linear correlation between positive‐channel growth and CC duration is found, providing evidence that the positive leader grows with a constant velocity, but no obvious correlation of this velocity with CC occurrence is found. Each return stroke is then sorted by its channel growth rate and further identified by its CC type. This analysis also provides no identifiable correlation linking the positive‐channel growth rate to CC occurrence or duration. Finally, the positive‐channel growth rate for the whole flash is calculated in 10 ms windows so that any trends occurring before, during, or after the CC can be observed. This analysis too shows no correlation, which implies that positive‐channel growth is not the primary mechanism that determines CC occurrence and duration.

Characteristics of current pulses in rocket-triggered lightning

The waveform parameters of current pulses in negative rocket-triggered lightning are analyzed statistically using recorded channel-base current during Shandong Artificially Triggered Lightning Experiment (SHATLE) from 2005 to 2011. The current pulses are divided into 3 categories, including return strokes, ICC pulses in initial continuous current (ICC) stage and M-components superimposed on the continuing current following the return stroke. The geometric mean values (GM) of peak current, risetime from 10% to 90% peak, half peak width and charge transfer for return strokes are 12.1kA, 1.0μs, 14.8μs, and 0.86C, respectively. The corresponding parameters for ICC pulses are 0.09kA, 437μs, 712μs, and 0.10C, respectively, while they are 0.28kA, 251μs, 242μs and 0.10C for M-components, respectively. There is significant fraction of larger M-components (about 10% of 63 samples) demonstrating peak current of several kilo-amperes, comparable to weak return strokes. The ICC pulses show somewhat lower current peak and slower risetime than the M-components with a difference of roughly 2–3 times, resulting from the lower charge source of ICC pulses. In general, the ICC pulses and M-components show smaller peak current and charge transfer while longer risetime and half peak width than return strokes, differing with 1–2 orders of magnitude. The charge neutralized by an individual triggered lightning flash ranged from 6.3C to 68.1C, while the initial stage (IS), lasted about 245ms (GM) and lowered a GM charge of 21.2C to the ground. The average IS current in an individual lightning discharge varies from 45.8A to 140.6A with a GM value of 86.7A.

Correlation analysis between the channel current and luminosity of initial continuous and continuing current processes in an artificially triggered lightning flash

Using simultaneous high-speed camera records and channel-base current records in an artificially triggered negative lightning event, the correlation between the channel-base current and the integrated luminosity (IL) of the air-ionized part of the lightning channel is analyzed during the periods of the initial continuous current (ICC) process and eight continuing current (CC) processes. Depending on the current's changing trend (ascending or descending) and the luminosity property of the pixels used to calculate the IL from the high-speed camera records (including saturated pixels or not), the ICC and eight CC processes are divided into the saturated ascending stage (Stage-A), the saturated descending stage (Stage-B), the unsaturated ascending stage (Stage-C) and the unsaturated descending stage (Stage-D), including the descending tail stage (Stage-T, in which the channel-base current falls to zero). The analysis shows the following: (1) the IL is linearly correlated with the logarithmic value of the current in both Stage-A and Stage-B of two long CC processes, the ICC process and the CC process after the 7th return stroke, although the regression parameters (intercept and slope) in Stage-B are higher than those in Stage-A. This rule can also be found in most pulses of the long CC processes, where the IL in the descending stage is higher than that in the ascending stage at the same current value, regardless of which threshold index or height range used to calculate the IL are selected and regardless of whether the IL includes saturated pixels or not. (2) In the unsaturated stage of long CC processes, the channel current shows a significant linear correlation with the square root of the IL, and the fit of this relationship is much better than that in the saturated stage. Additionally, in each Stage-T of the eight CC processes following return strokes, the square root of the IL is significantly and linearly correlated with the current, and the regression slope is negatively correlated with the corresponding return stroke peak current. This result means that for the same channel current variation, the lower the return stroke peak current associated with the Stage-T of the CC process, the greater the luminosity variation. (3) For each of the above stages, the statistical model has a better fit when a higher threshold index, a more perpendicular channel or a greater height range is selected in the calculation of the IL.

Transient luminous events above two mesoscale convective systems: Charge moment change analysis

[1] Charge moment change (ΔMQ) data were examined for 41 positive cloud-to-ground (+CG) lightning discharges that were parents of transient luminous events (TLEs; mainly sprites) over two different storms: 9 May (20 parents) and 20 June 2007 (21). Data were broken down by contributions from the impulse ΔMQ (iΔMQ), within the first 2 ms of the return stroke, and the ΔMQ from the continuing current (CC), which can last tens of ms afterward. Three-dimensional lightning mapping data provided positions for the in-cloud components of the parent +CGs. Charge and charge density neutralized by the strokes were estimated. The 20 June parents were more impulsive than 9 May, with increased iΔMQ and CC amplitude but reduced CC duration. Total ΔMQ values between the two storms were very similar, averaging ∼1800 C km. Estimated charge density on 20 June was nearly twice that on 9 May, consistent with the 20 June storm being more intense with a stronger electrical generator. Lightning metrics were analyzed for 9 high- iΔMQ (>300 C km) +CGs that did not produce an observable TLE on 20 June, and compared to that day's TLE parents. Non-TLE +CGs had reduced CC magnitudes and duration, with less total ΔMQ. Photogrammetric estimates of TLE azimuthal swaths were positively correlated with similar metrics of the in-cloud portions of the parent +CGs, as well with total ΔMQ. The implications of all these results for the ΔMQ theory of sprite initiation, and for the relationship between sprite development and in-cloud discharging, are discussed.

Computer simulations on sprite initiation for realistic lightning models with higher‐frequency surges

Computer simulations on transient luminous emissions in the mesosphere and lower ionosphere have been performed for realistic lightning modelings with fast‐varying current surges (M components) superimposed on the lightning continuing current (CC). The algorithm used here is an electromagnetic (EM) code, which enables us to estimate self‐consistently the reduced electric field, electron density, conductivity, and luminosity as a function of space and time by solving the Maxwell equations. It is found that M components in the CC with small amplitudes, but with a fast‐varying EM effect, can initiate or enhance the occurrence of sprites. Even for a return stroke (RS) without CC, subsequent high‐frequency current variations (like M components) are found to lead to dramatic changes in the sprite occurrence. The physics underlying these changes is studied by means of, e.g., temporal and spatial variations of luminosity, electron density, and conductivity. As the conclusion, the RS is a fundamental agency for spites, but high‐frequency variations as EM effects exhibit an additional essential influence on sprite occurrence. These computational results are used to offer some useful ideas concerning the unsolved problems of sprites and halos, including polarity asymmetry, long‐delay characteristics, and morphological shapes of sprites.

Continuing current in multiple channel cloud-to-ground lightning

In this study we analyze the effects of continuing current initiated by strokes following a new channel to ground in multiple stroke flashes using high-speed video records, electric field measurements from a fast antenna and lightning detection network data. We observed that the long continuing current initiated by a stroke that follows a new channel also obeys the pattern in the initiation of long continuing current suggested by Rakov and Uman [Rakov, V.A., Uman, M.A., 2003. Lightning: Physics and Effects, 687pp., Cambridge Univ. Press, New York.]. We also verify that the statement of Rakov and Uman [Rakov, V.A. and Uman, M.A., 1990. Some properties of negative cloud-to-ground lightning flashes versus stroke order, Journal of Geophysical Research. 95, 5447–5453.] reporting that: “...strokes initiating long continuing currents tend to have lower initial electric field peak than regular strokes” is valid for strokes that create a new channel to ground and are followed by long continuing current (CC). Apparently the reduction of peak current value ( I p) when the stroke is followed by a long CC is stronger than the I p increase that is commonly observed when strokes follow a new channel. We also find that the “exclusion zone” proposed by Saba et al. [Saba, M.M.F., Pinto, O. Jr., Ballarotti, M.G., 2006a. Relation between lightning return stroke peak current and following continuing current, Geophysical Research Letters 33, L23807, doi:10.1029/2006GL027455.] is valid for new channels initiating CC, and finally we verify that a number of strokes in the same channel larger than four or the existence of a long CC current do not always consolidate the channel in a multiple stroke flash.

Relation between lightning return stroke peak current and following continuing current

The magnitude of the return stroke peak current preceding continuing current (CC) in ground flashes was investigated. This study was performed using a high‐speed camera (1,000 frames/s), an electric field flat‐plate antenna and data provided by the Brazilian Lightning Detection Network (RINDAT). The observation of 454 negative strokes followed by CC with durations from 4 ms to 542 ms revealed that negative strokes combining both peak current greater than 20 kA and CC greater than 40 ms are highly unlikely to occur. However, this was found to be possible for positive strokes. In addition, we found that on average the longer the CC, the lower the return stroke peak current preceding it. Therefore, the average detection efficiency of RINDAT was found to decrease from 62% for negative strokes followed by very‐short CC (less than 10 ms) to 36% for strokes followed by long CC, with an intermediate value of 57% for strokes followed by short (from 10 to 40 ms) CC.

Acute disseminated lupus erythematosus, without cutaneous manifestations and with heretofore undescribed pulmonary lesions: Rakov, H. L., and Taylor, J. S.: Arch. Int. Med. 70: 88, 1942

In this study we analyze the effects of continuing current initiated by strokes following a new channel to ground in multiple stroke flashes using high-speed video records, electric field measurements from a fast antenna and lightning detection network data. We observed that the long continuing current initiated by a stroke that follows a new channel also obeys the pattern in the initiation of long continuing current suggested by Rakov and Uman [Rakov, V.A., Uman, M.A., 2003. Lightning: Physics and Effects, 687pp., Cambridge Univ. Press, New York.]. We also verify that the statement of Rakov and Uman [Rakov, V.A. and Uman, M.A., 1990. Some properties of negative cloud-to-ground lightning flashes versus stroke order, Journal of Geophysical Research. 95, 5447–5453.] reporting that: “...strokes initiating long continuing currents tend to have lower initial electric field peak than regular strokes” is valid for strokes that create a new channel to ground and are followed by long continuing current (CC). Apparently the reduction of peak current value (Ip) when the stroke is followed by a long CC is stronger than the Ip increase that is commonly observed when strokes follow a new channel. We also find that the “exclusion zone” proposed by Saba et al. [Saba, M.M.F., Pinto, O. Jr., Ballarotti, M.G., 2006a. Relation between lightning return stroke peak current and following continuing current, Geophysical Research Letters 33, L23807, doi:10.1029/2006GL027455.] is valid for new channels initiating CC, and finally we verify that a number of strokes in the same channel larger than four or the existence of a long CC current do not always consolidate the channel in a multiple stroke flash.