Preliminary Breakdown Pulses Research Articles

Transform of Lightning Electromagnetic Pulses Based on Laplace Wavelet

In this study, the fine structures of lightning electromagnetic pulse associated with 19 preliminary breakdown pulses, 37 stepped leaders, 8 dart leaders, 73 first and 52 subsequent return strokes were analyzed by using Laplace wavelet. The main characteristics of field waveforms such as, the correlation coefficient, the time of arrival and the dominant frequency of the initial peak field, the energy and the frequency of the power spectrum peak are presented. The instantaneous initial peak field pulse can be precisely located by the value of the correlation coefficient. The dominant frequencies of the initial peak field of PB pulses and leaders range from 100 kHz to 1 MHz, and that of the first and subsequent return strokes below 100 and 50 kHz, respectively. The statistical results show that the Laplace wavelet is an effective tool and can be used to determine time and frequency of the lightning events with greater accuracy. DOI: http://dx.doi.org/10.11591/telkomnika.v11i9.2867

Preliminary breakdown pulses of cloud-to-ground lightning in winter thunderstorms in Japan

Preliminary breakdown pulses (PBP) of 26 positive and 104 negative cloud-to-ground (CG) lightning flashes observed in winter thunderstorms in Hokuriku region of Japan are analyzed. Pulses in PBP train are mainly bipolar. Zero-crossing time of each pulse is about 7us and total duration of each pulse train is about 1ms. PBPs in negative CG lightning are classified as “BIL type” (59 cases) and “BL type” (45 cases). “BIL type” PBP contains an intermediate stage with little electric field changes. The time interval between PBP and the first return stroke (PBP–RS interval) is on average 5.4ms for “BIL type” PBP, while that for “BL type” PBP is only 1.3ms. Ratio of peak amplitude of PBP to the first return stroke (PBP–RS ratio) is on average 0.47 and 0.44, respectively, for “BIL type” and “BL type” PBPs, but the ratio for “BIL type” PBP has a much wider distribution. It is speculated that the intermediate stage in “BIL type” PBP is caused by horizontal propagation of leader channel. PBPs in positive CG lightning are classified as +PBP (11 cases) and −PBP (15 cases) according to their initial polarities. +PBP and −PBP have similar distributions of both PBP–RS interval and PBP–RS ratio, but their value of PBP–RS interval is much larger and their value of PBP–RS ratio is much smaller than corresponding values of PBPs in negative CG lightning. It is speculated that different initial polarities of +PBP and −PBP in positive CG lightning are caused by different directions of channel propagation.

Reconstruction of lightning channel geometry by localizing thunder sources

Thunder is generated as a result of a shock wave created by sudden expansion of air in the lightning channel due to high temperature variations. Even though the highest amplitudes of thunder signatures are generated at the return stroke stage, thunder signals generated at other events such as preliminary breakdown pulses also can be of amplitudes which are large enough to record using a sensitive system. In this study, it was attempted to reconstruct the lightning channel geometry of cloud and ground flashes by locating the temporal and spatial variations of thunder sources. Six lightning flashes were reconstructed using the recorded thunder signatures. Possible effects due to atmospheric conditions were neglected. Numerical calculations suggest that the time resolution of the recorded signal and 10ms−1error in speed of sound leads to 2% and 3% errors, respectively, in the calculated coordinates. Reconstructed channel geometries for cloud and ground flashes agreed with the visual observations. Results suggest that the lightning channel can be successfully reconstructed using this technique.

Electric fields changes produced by positives cloud-to-ground lightning flashes

Positive flashes correspond to approximately only 10% of the total number of flashes produced by a thunderstorm. However, strokes with high peak currents and long continuing currents are usually present in positive flashes. Therefore, positive flashes are responsible for more intense damage than the negative ones. Positive flashes often are preceded by significant and long duration intracloud (IC) discharge activity. We observe in detail the electric field variations produced by 80 cloud-to-ground lightning flashes in 9 different storms in S. Paulo, Brazil during the summers of 2009–2011. Intracloud discharges preceding the positive cloud-to-ground flashes and some characteristics of the electric field changes produced by the return stroke that occurred at ranges of 3–80km from the site of the electric field measurements were analyzed. All flashes presented breakdown pulses prior to the return stroke. The mean time interval between the preliminary breakdown pulse (PBP) and return stroke was 157ms. The pulse train duration have a mean value of 3.1ms. Only 6 out of 80 cases analyzed did not present pulse trains but only one single bipolar breakdown pulse before the return stroke. In 95% of cases the initial breakdown pulse presented the same initial polarity of the succeeding return stroke. Time interval between pulses in a pulse train had a mean value of 280μs. The mean values of pulse width is 25.2μs. The mean values of zero-to-peak risetimes and of the 10–90% risetimes for 72 return strokes electric field waveforms are 9.5 and 5.7μs respectively. The AM value of peak amplitudes of the positive return strokes fields normalized to 100km is 17.0V/m.

Electric field changes generated by the preliminary breakdown for the negative cloud-to-ground lightning flashes in Malaysia and Sweden

We present the study of the electric field changes generated by the preliminary breakdown for negative cloud-to-ground lightning flashes in Malaysia and Sweden concerning the association of slow field changes associated in preliminary breakdown process. We examined the total of 1685 negative cloud-to-ground lightning flashes from the total of 39 thunderstorms by recording the slow electric field, fast electric field and narrowband radiation field at 3 and 30MHz signals simultaneously. Our results show that there is a pre-starting time, i.e. the duration between the first preliminary breakdown pulse and slow field changes starting point, which is found to be after the first preliminary breakdown pulse. The pre-starting time has the arithmetic and geometric mean range from 1.4–6.47 and 1–3.36ms, respectively. The mean values of pre-starting time in Malaysia are greater than the values observed in Sweden by more than a factor of 3. From the two data sets it shows that the slow field changes never start before the preliminary breakdown. Furthermore, the use of single-station electric fields measurement with high resolutions of 12 bits transient recorder with several nanosecond accuracy allow one to distinguish the slow field changes generated by preliminary breakdown, which preceded the negative first return stroke, between tens to hundreds of milliseconds of pre-return stroke duration.

Positive lightning: An overview, new observations, and inferences

We examine the various conceptual cloud charge configurations and scenarios leading to production of positive lightning with a view toward an explanation of its observed properties. Data for 52 positive cloud‐to‐ground flashes containing 63 strokes recorded in Gainesville, Florida, in 2007–2008 are presented and discussed. The U.S. National Lightning Detection Network (NLDN) located 51 (96%) of the positive strokes at distances of 7.8 to 157 km from the field‐measuring station. In 42 (81%) of the 52 flashes, the first (or the only) leader‐return stroke sequence was not preceded by in‐cloud discharge activity. The average number of strokes per flash is 1.2. Single‐stroke flashes constitute 81%. In three (38%) of eight two‐stroke flashes, the second stroke likely followed the channel of the first stroke, and in five (62%) flashes it likely created a new termination on ground. Eight (15%) of the 52 positive flashes had detectable preliminary breakdown pulse trains in their electric field records. Electric field waveforms of 14 (27%) first strokes (also of one third stroke) are preceded by pronounced pulses, apparently indicative of leader stepping. NLDN‐reported peak currents for 48 positive strokes in 40 flashes ranged from 20 to 234 kA with a geometric mean value of 75 kA. The median charge transfers in 1, 2, and 40 ms after the beginning of return stroke electric field change for an assumed height of 12 km were estimated to be 13, 18, and 34 C, respectively. Two bipolar lightning discharges are additionally examined.

Comparative study on preliminary breakdown pulse trains observed in Johor, Malaysia and Florida, USA

In this paper, the preliminary breakdown (PB) pulse train preceding the negative first return stroke (RS) is recorded using a broad band antenna system. These analyses were carried out in Johor Bahru, Malaysia and Florida, United States. This is a novel initiative at examining and identifying the characteristics of the PB pulse trains in the negative cloud-to-ground flashes observed in Malaysia. The arithmetic mean of the total pulse train duration is 12.3ms and the weighted arithmetic mean of the pulse durations and interpulse intervals are 11μs and 152μs, respectively. The arithmetic mean ratio between the maximum peak amplitude of the PB pulse and the peak RS electric field was 27.8%, and the corresponding value in Florida was 29.4%. The arithmetic mean of the time duration between the most active part of the pulse train, and the RS was 57.6ms in Malaysia and 22ms in Florida. A qualitative comparison of our results with those obtained earlier in Sri Lanka, Sweden and Finland supports the hypothesis that the PBP/RS ratio is higher in the northern regions compared to the tropical regions.

Some inferences on the role of lower positive charge region in facilitating different types of lightning

It is generally thought that the lower positive charge region serves to enhance the electric field at the bottom of the main negative charge region and thereby facilitate the launching of a negatively‐charged leader toward ground. On the other hand, the presence of excessive lower positive charge region may prevent the occurrence of negative cloud‐to‐ground discharges by “blocking” the progression of descending negative leader from reaching ground and thus “converting” the potential cloud‐to‐ground flash to an intracloud (or cloud‐to‐air) one. Assuming that the preliminary breakdown pulse train is a manifestation of interaction of a downward‐extending negative leader channel with the lower positive charge region, we qualitatively examine the inferred dependence of lightning type on the magnitude of this charge region.

Electric Field Pulse Trains Occurring Prior to the First Stroke in Negative Cloud-to-Ground Lightning

In this study, we examine the characteristics of electric field pulse trains that are attributed to preliminary breakdown in negative cloud-to-ground lightning discharges and compare them to those of similar pulse trains associated with attempted cloud-to-ground leaders. The data were acquired in 2006 in Gainesville, Florida. The largest pulses in the train can exceed in magnitude the following first return-stroke pulse. The arithmetic mean pulse duration and interpulse interval for pulse trains in negative cloud-to-ground discharges are 4.8 and 65 mus, respectively. The arithmetic mean pulse duration and interpulse interval for pulse trains in attempted cloud-to-ground leaders are 17 and 73 mus, respectively. This implies that pulse trains in ground discharges contain a larger fraction of ldquonarrowrdquo pulses (apparently disregarded in previous studies), defined here as those with durations equal to or less than 4 mus, than the pulse trains in attempted cloud-to-ground leaders. Submicrosecond-scale pulses are observed as part of pulse trains associated with cloud-to-ground discharges, but not with attempted leaders. We also examine the occurrence of pulses of different duration and amplitude in different parts of the preliminary breakdown pulse train of ground discharges. Pulses with larger durations (>4 mus) tend to occur in the initial part of pulse train.

Analysis of microsecond- and submicrosecond-scale electric field pulses produced by cloud and ground lightning discharges

We examined microsecond- and submicrosecond-scale pulses in electric field records of cloud and cloud-to-ground lightning discharges acquired in summer 2006, in Gainesville, Florida. A total of 12 cloud and 12 ground flashes were analyzed in detail, with the electric field record length being 96 or 200 ms and sampling interval being 4 or 10 ns. The majority of pulses in both cloud and ground discharges analyzed in this study were associated with the initial breakdown process and were relatively small in amplitude and duration. The typical durations were an order of magnitude smaller than tens of microseconds characteristic of “classical” preliminary breakdown pulses. We estimated that 26% of the pulses in the 12 cloud discharges and 22% of the pulses in the 12 cloud-to-ground discharges had total durations less that 1 µs.

Pulse trains that are characteristic of preliminary breakdown in cloud‐to‐ground lightning but are not followed by return stroke pulses

In this study, we identify and examine electric field pulse trains that are characteristic of preliminary breakdown in negative cloud‐to‐ground discharges but are not followed by return stroke waveforms. We assume that such trains are manifestations of the initiation of downward negative stepped leaders that fail to propagate all the way to the ground and refer to these events as “attempted first cloud‐to‐ground leaders,” although some of them were followed by full‐fledged cloud discharges. We examined a total of 2475 electric field records of lightning events acquired in Gainesville, Florida, in 2006, and waveforms in 33 of them were found to satisfy criteria set for attempted cloud‐to‐ground leaders. In addition to pronounced bipolar pulses with positive (atmospheric electricity sign convention) initial half cycle, negative unipolar and negative (initial half cycle) bipolar pulses were sometimes seen toward the end of the train. We also observed that at the beginning and at the end of the pulse train, there were narrower pulses, often having durations in the range of 1–2 μs, which are more than an order of magnitude shorter than for “classical” preliminary breakdown pulses. The arithmetic mean of total pulse train durations is 2.7 ms, and the weighted arithmetic means of individual pulse durations and interpulse intervals are 17 and 73 μs, respectively. Some of the attempted cloud‐to‐ground leaders, which should belong to the cloud discharge category, can be misclassified as negative cloud‐to‐ground discharges by lightning locating systems such as the U.S. National Lightning Detection Network.

Radiation field pulses associated with the initiation of positive cloud to ground lightning flashes

Seventy one electric field pulse trains that occurred during millisecond-scale time intervals before positive cloud to ground lightning flashes were analysed. These pulses are bipolar in nature and somewhat similar in pulse characteristics to the breakdown pulses preceding negative cloud to ground lightning. However, in the case of these positive flashes, the pulse characteristics of the pulse trains are confined in a much wider range of values than those of the pulse trains associated with negative return strokes. The leading edge of the pulses of the most commonly observed pulse trains that precede positive return strokes are relatively smooth, thus, different from their counterparts associated with negative flashes, in which case a few narrow pulses are superimposed on the rising edge of the bipolar pulses. Considering the initial polarity of pulses, four types of bipolar pulse trains preceding positive return strokes were identified. For each type of pulse trains, statistics of pulse characteristics were given. In contrast, in the case of negative ground flashes, the bipolar pulse trains were almost always composed of pulses of the same polarity as that of the succeeding return stroke. The possible causes of the observation of several types of pulse trains and the significantly diversified pulse characteristics of the breakdown pulse trains of positive flashes were discussed. The frequency spectrum of the electric fields of the most common type of pulse trains was compared with the spectrum of the breakdown pulses of negative flashes and those of negative return strokes. This spectrum of the preliminary breakdown pulse trains of positive ground flashes is comparable with that of the preliminary breakdown pulse trains of negative ground flashes.

Electromagnetic pulse environment of cloud-to-ground lightning for EMC studies

The characteristics of lightning electromagnetic pulse (LEMP) from individual processes in lightning such as return strokes, preliminary breakdown pulses, pulses associated with the leader process, K-changes and M-changes, the isolated narrow bipolar pulses, and the pulse bursts have been known. However, there is a need for a combined characterization of the total LEMP environment created during the entire duration of lightning. An attempt is made to provide such a description that gives the distribution of the LEMP characteristics, which is important in its ability to interfere with electronic systems, such as peak amplitude, peak time derivative, pulse duration, number of pulses, and time interval between pulses, during the entire duration of a cloud-to-ground lightning. Separate electromagnetic environment characterizations for negative cloud-to-ground lightning and positive cloud-to-ground lightning are proposed, including all the significant LEMP sources. Based on the LEMP characterization, models for negative and positive cloud-to-ground lightning flashes, that could be used in electromagnetic compatibility (EMC) studies are proposed. The electromagnetic environment models for cloud-to-ground lightning can be coupled to the locations of lightning given by the lightning location system to give comprehensive information about the electromagnetic environment at a desired geographical location.

Comparison of preliminary breakdown pulses observed in Sweden and in Sri Lanka

In this paper we have analysed breakdown pulse trains preceding the first return stroke in 47 negative cloud-to-ground (CG) lightning flashes observed in Sri Lanka (tropics) and that in 41 negative CG flashes recorded in Sweden (temperate regions). In the data obtained in Sri Lanka, breakdown pulses could be detected only in nine flashes. In other flashes either these pulses are absent or, if they are present, their amplitudes should be below the background noise level. From the nine flashes with breakdown pulse trains, we obtained the following results. The ratio between the maximum breakdown pulse amplitude and the return stroke amplitude (BP\RS ratio), as a percentage, is 16.5%. The time duration between the most active part of the pulse train and the return stroke (BP\RS separation), is 11.9 ms and the ratio between the noise amplitude and the return stroke amplitude (N\RS ratio), as a percentage, for all 47 flashes, is 5.0%. In the flashes observed in Sweden, breakdown pulses are detectable in all records. In this data, the BP\RS ratio, as a percentage, is 101.4%, the BP\RS separation is 13.8 ms and the N\RS ratio, as a percentage, is 3.7%. All the above values are arithmetic means. Most of the pulses of breakdown pulse trains observed in both countries are bipolar in nature with the initial polarity the same as that of the succeeding return stroke.