2010

Pichler H., G. Diendorfer, M. Mair:
Some Parameters of Correlated Current and Radiated Field Pulses from Lightning to the Gaisberg Tower

IEEJ Transactions on Electrical and Electronic Engineering, 5: 8–13, Published online in Wiley InterScience ,  DOI:10.1002/tee.20486, 2010

Simultaneous measurements of lightning current and associated radiated electromagnetic field are of fundamental interest for various applications in lightning research. These data can be used for the evaluation of return stroke (RS) models or to investigate the so-called tower effect when lightning hits an elevated object. In this paper, we show the results of simultaneous measurements of current pulses from lightning strikes on the instrumented Gaisberg tower (Austria) and the correlated vertical E-field components at a distance of 78.8 and 108.7 km, respectively. We have analyzed some main lightning current parameters (peak current Ip, 30–90% rise time TI–30−90, and full width at half maximum TI–FWHM) and the time-correlated field waveform parameters (Ep, 30–90% rise time TE–30−90, TE–FWHM, and the peak-to-zero time TE–PTZ). With a geometric mean of TI–FWHM = 19 μs and Ip = 9.6 kA (N = 73) of the RS current pulses used in this study, those strokes are very similar to the strokes in triggered lightning in Florida and Alabama [1]. With a TE–PTZ of about 10 μs, the zero-crossing time of the radiated E-fields from the tower strokes are significantly shorter than the typical values of 30 − 40 μs (e.g. [2]). Correlation between the current and field parameters TI–FWHM versus TE–FWHM and TE–PTZ, respectively, is low (R2 = 0.29 and 0.14). We assume that the relatively short lightning channel in the case of the RSs in object-triggered upward flashes is the main reason for the observed short zero-crossing time. © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

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Zhou H., G. Diendorfer, R. Thottappillil, H. Pichler, M. Mair:
Simultaneous Current and Electric Field Observations of Upward Negative Leaders Initiated from the Gaisberg Tower

Asia-Pacific International Symposium on Electromagnetic Compatibility (APEMC), Beijing, China, 2010

In this paper, we present simultaneous current and electric field records of two upward negative leaders initiated from the Gaisberg Tower (GBT). It is shown that bipolar current pulses occur at the beginning of the upward negative leaders followed by regular unipolar leader pulse trains, and the corresponding electric field exhibits asymmetrical V-shaped pulses with a hump superimposed at the end of the pulse. The stepped leader characteristics in electric field waveforms at close range are similar to that of downward stepped leader pulses in altitude-triggered lightning flashes. Distinct electric field changes prior to the upward negative leader inception are indicative of nearby lightning discharges.

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Fiser J., J. Chum, G. Diendorfer, M. Parrot, O. Santolik:
Whistler intensities above thunderstorms

Annales Geophysicae, 28, 37–46, 2010

We report a study of penetration of the VLF electromagnetic waves induced by lightning to the ionosphere. We compare the fractional hop whistlers recorded by the ICE experiment onboard the DEMETER satellite with lightning detected by the EUCLID detection network. To identify the fractional hop whistlers, we have developed software for automatic detection of the fractional-hop whistlers in the VLF spectrograms. This software provides the detection times of the fractional hop whistlers and the average amplitudes of these whistlers. Matching the lightning and whistler data, we find the pairs of causative lightning and corresponding whistler. Processing data from ~200 DEMETER passes over the European region we obtain a map of mean amplitudes of whistler electric field as a function of latitudinal and longitudinal difference between the location of the causative lightning and satellite magnetic footprint. We find that mean whistler amplitude monotonically decreases with horizontal distance up to ~1000 km from the lightning source. At larger distances, the mean whistler amplitude usually merges into the background noise and the whistlers become undetectable. The maximum of whistler intensities is shifted from the satellite magnetic footprint ~1° owing to the oblique propagation. The average amplitude of whistlers increases with the lightning current. At nighttime (late evening), the average amplitude of whistlers is about three times higher than during the daytime (late morning) for the same lightning current.

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Diendorfer G.:
LLS Performance validation using lightning to Towers

21st International Lightning Detection Conference and 3rd International Lightning Meteorology Conference (ILDC/ILMC), Orlando, Florida, 2010

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Diendorfer G., W. Schulz, H. Umprecht, H. Pichler:
Effect of Tower initiated lightning on the ground stroke density in the vicinity of the Tower

21st International Lightning Detection Conference and 3rd International Lightning Meteorology Conference (ILDC/ILMC), Orlando, Florida, 2010

Detailed comparison of located lightning strokes in a 10 km radius area and directly measured lightning currents to the instrumented Gaisberg Tower (GBT) located in the centre of that area is presented. In 84% of the days, when lightning was measured at the GBT, no thunderstorm (TS) activity was observed in the surrounding area. On the other hand, no lightning events at the GBT were recorded in 77 % of the days, when TS activity was present in the area. Upward initiated lightning from the GBT occurs more or less independent of the general CG activity in the area and we conclude that elevated objects neither reduce nor increase the number of strokes to ground in the objects vicinity significantly. Any additional lightning initiated by the object hits directly the object.

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Saba M.M.F., W. Schulz, L.Z.S. Campos:
M components or cloud-to-ground subsequent strokes?

21st International Lightning Detection Conference and 3rd International Lightning Meteorology Conference (ILDC/ILMC), Orlando, Florida, 2010

From the analysis of digital high-speed videos and electric field records of two flashes, some relationships are presented between the channel luminosity preceding the occurrence of the luminosity pulse and the characteristics of the related electric field signature. Some M components may produce E-field signatures very similar to those produced by subsequent return strokes if the preceding luminosity of channel flash is very faint. These M components may be detected by LLS. If the channel luminosity is high, that is, if the continuing current flowing through it is high, then the E-field signature is different from the signature of a subsequent return stroke. The luminosity intensity preceding each M component along with its 10-90% risetime, estimated peak current and peak E-field are presented.

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Mosaddeghi A., A. Shoory, F. Rachidi, G. Diendorfer, H. Pichler, D. Pavanello, M. Rubinstein, P. Zweiacker, M. Nyffeler:
Lightning electromagnetic fields at very close distances associated with lightning strikes to the Gaisberg

Journal of Geophysical Research: Atmospheres, Vol. 115, D17101, doi:10.1029/2009JD013754, 2010

In this paper we present and discuss measurements of electric (vertical and radial) and magnetic fields from leaders and return strokes associated with lightning strikes to the 100 m tall Gaisberg tower in Austria obtained in 2007 and 2008. The fields were measured at a distance of about 20 m from the tower. Simultaneously, return stroke currents were also measured at the top of the tower. The data include, for the first time at such close distances, simultaneous records of vertical and horizontal electric fields. The vertical electric field waveforms appeared as asymmetrical V-shaped pulses. The initial, relatively slow, negative electric field change is due to the downward leader, and the following, fast, positive electric field change is due to the upward return stroke phase of the lightning discharge. The horizontal (radial) electric field due to the leader phase has a waveshape similar to that of the vertical electric field. However, the horizontal field due to the return stroke is characterized by a short negative pulse of the order of 1 ms or so, starting with a fast negative excursion followed by a positive one. The return stroke vertical electric field changes appear to be significantly smaller than similar measurements obtained using triggered lightning. This finding confirms the shadowing effect of the tower, which results in a significant decrease of the electric field at distances of about the height of the tower or less. The vertical and horizontal E field changes due to the return stroke were also found to be larger on average than the leader electric field changes. In a significant number of cases (33%), the vertical electric field waveforms due to the return stroke were characterized by a first peak exceeding the typical late-time flattening due to the electrostatic term. This is in contrast with similar measurements related to triggered lightning which do not exhibit such a first peak. About one quarter of the measured vertical electric field waveforms (18 pulses out of 76) featured an unusual waveform characterized by a positive leader field change followed by a bipolar return stroke field change with a zero crossing time of about 60 ms.

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Zhou H., N. Theethayi, G. Diendorfer, R. Thottappillil, V.A. Rakov:
On estimation of the effective height of towers on mountaintops in lightning incidence studies

Journal of Electrostatics 68, 415e418, 2010

Towers on mountaintops have more incidence of lightning than towers on the flat ground. Therefore towers on mountaintops are ascribed an effective height that is often considerably larger than the physical height of the tower.

In this paper, we review and evaluate the definitions and methods that could be used to estimate the effective height of a given tower on mountaintop and propose a new definition based on an engineering model of lightning attachment. The results can be useful in designing lightning protection of communication/transmission lines and masts on mountaintops.

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Zhou H., G. Diendorfer, R. Thottappillil, H. Pichler, M. Mair:
Continuing current in Tower-initiated lightning

30th International Conference on Lightning Protection (ICLP), Cagliari, Italy 2010

We investigate 172 upward-initiated negative lightning flashes containing at least one leader-return stroke sequence observed to the Gaisberg Tower (GBT) in Austria from 2000 to 2009. A geometric mean value of 8.75 kA of the return stroke peak current is determined, followed by a continuing current of 1.48 ms with a charge transfer of 0.786 C. We find that in case of the continuing current duration larger than 40 ms, usually defined as long continuing current, or when the continuing current charge transfer is greater than 5 C, the initiating peak return stroke current did not exceed 20 kA. Moreover, continuing currents with durations of less than 20 ms or with a charge transfer smaller than 5 C, those continuing currents were initiated by return strokes with peaks of any range.

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Zhou H., G. Diendorfer, R. Thottappillil1, H. Pichler, M. Mair:
Upward bipolar lightning flashes observed at the Gaisberg Tower

30th International Conference on Lightning Protection (ICLP), Cagliari, Italy 2010

We analyze current records for 21 natural upward-initiated bipolar lightning flashes observed to the Gaisberg Tower (GBT) in Austria from 2000 to 2009. Thirteen (62%) of 21 bipolar flashes occurred in non-convective season (September- March) and twelve (57%) of them occurred in seasonal transmission periods of March, August, and November in Austria. Thirteen (62%) of them belong to Type 1 associated with a polarity reversal during the initial stage current, based on the classification as suggested by Rakov and Uman [1]. We also find that the initial polarity reversal from negative to positive occurs more often (16 of 21) than that from positive to negative within a bipolar flash, in agreement with observations in other studies. The geometric mean total absolute charge transfer is 99.5 C with a relatively short total duration of 320 ms.

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Manoochehrnia P., F. Rachidi, M. Rubinstein, W. Schulz, G. Diendorfer:
Benford´s law and lightning data

30th International Conference on Lightning Protection (ICLP), Cagliari, Italy, 2010

Lightning data in Switzerland obtained using the European Cooperation for Lightning Detection (EUCLID) network are used to investigate the applicability of the Benford’s law to lightning data. The considered data set consists of the peak current estimates and interstroke intervals. It is shown that the obtained distributions are in good agreement with Benford’s law.

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Schulz W., H. Pichler, G. Diendorfer:
Evaluation of 45 negative flashes based on E-field measurements, video data and lightning location data in Austria

30th International Conference on Lightning Protection (ICLP), Cagliari, Italy 2010

In this paper we present an analysis of 45 negative flashes based on video and field measurement data. The analysis based on video and E-field measurement data is an ideal method to check lightning location data in terms of cloud-to-cloud or cloud-to-ground classification. We will show that the flash and stroke detection efficiency determined by this analysis is quite similar to the result from measurements at the Gaisberg Tower. We further present some lightning parameters for negative flashes and compare them to values available in the literature.

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Mosaddeghi A., A. Shoory, F. Rachidi, G. Diendorfer, H. Pichler, D. Pavanello, M. Rubinstein, P. Zweiacker, M. Nyffeler:
Vertical and radial electric fields from leaders and return strokes associated with lightning strikes to the Gaisberg Tower

30th International Conference on Lightning Protection (ICLP), Cagliari, Italy 2010

We present and discuss measurements of electric fields (vertical and radial) from leaders and return strokes associated with lightning strikes to the Austrian Gaisberg Tower (GBT) obtained in 2008. The fields were measured at a distance of about 20 m from the tower. Simultaneously with the fields, return-stroke currents were also measured at the top of the tower. The vertical electric field waveforms appeared as asymmetrical V-shaped pulses. The initial, relatively slow, negative electric field change is due to the downward leader and the ensuing fast positive field change is due to the upward return stroke phase of the lightning discharge. The horizontal (radial) electric field due to the leader phase has a similar waveshape to the vertical electric field. However, the radial field due to the return stroke is characterized by a short negative pulse of the order of 1 microsecond or so, starting with a fast negative excursion followed by a positive one.

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Saba M.M. F., W. Schulz, T.A. Warner, L.Z.S. Campos, R. Orville, E.P. Krider, K.L. Cummins, C. Schumann:
High-speed video observations of positive lightning flashes

30th International Conference on Lightning Protection (ICLP), Cagliari, Italy 2010

Although positive lightning flashes to ground are not as frequent as negative flashes, their large amplitudes and destructive characteristics make understanding their parameters an important issue. This study summarizes the characteristics of 103 positive cloud-to-ground (+CG) flashes that have been recorded using high-speed video cameras (up to 8000 frames per second) in three countries together with time-correlated data provided by lightning location systems (LLS). A large fraction of the +CG flashes (81%) produced just a single-stroke, and the average multiplicity was 1.2 strokes per flash. All the subsequent strokes in multiple-stroke +CG flashes created a new ground termination except one. 75% of the +CG flashes contained at least one long continuing current (LCC) ³ 40 ms, and this percentage is significantly larger than in the negative flashes that produce LCCs (approximately 30%). The median estimated peak current, (Ip) for 116 positive strokes that created new ground terminations was 39.4 kA. Positive strokes with a large Ip were usually followed by a LCC, and both of these parameters are threats in lightning protection. The characteristics presented here include the multiplicities of strokes and ground contacts, the percentage of single-stroke flashes, the durations of the continuing current, and the distributions of Ip.

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Mosaddeghi A., A. Shoory, F. Rachidi, M. Rubinstein, G. Diendorfer, H. Pichler, D. Pavanello, M. Nyffeler:
Close-Range Electric Fields Associated with Lightning Strikes to the Austrian Gaisberg Tower

International Journal of Plasma Environmental Science & Technology: I.J.PEST, 2010

We present measurements of very close vertical and horizontal electric fields from leaders and return strokes associated with lightning strikes to the 100-m tall Gaisberg tower in Austria obtained in 2007 and 2008. Simultaneously with the fields, return-stroke currents were also measured at the top of the tower. The vertical and horizontal electric field waveforms appeared as asymmetrical V-shaped pulses, the leading edge being slower than the trailing edge. The width of the V for the horizontal electric field is much smaller than that of the vertical electric field. Due to the shadowing effect of the tower, the return-stroke vertical electric field changes appear to be significantly smaller than similar measurements obtained using triggered lightning.

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Manoochehrnia P., F. Rachidi, M. Rubinstein, W. Schulz, G. Diendorfer:
Benford’s Law and Its Application to Lightning Data

IEEE Trans. Electromagn. Compat., DOI 10.1109/TEMC.2010.2067218, 2010

Benford’s law applies to a wide variety of natural and man-made datasets and it has been successfully applied to test the integrity of data and to detect possible fraud and anomalous results in economy, politics, and management studies. In this paper, we investigate the applicability of Benford’s law to lightning data. To do this, we use lightning data in Switzerland obtained using the European Cooperation for Lightning Detection (EUCLID) network. The considered dataset consists of the cloud-to-ground flashes in Switzerland for the period from 1999 till 2007. First the total number of negative and positive flashes per day is considered in the analysis. It is shown that the obtained distribution is in very good agreement with Benford’s law. The same analysis is repeated considering in the dataset only the flashes containing return strokes with absolute peak currents lower than 5 kA, for which the detection efficiency of the lightning location network is expected to be lower. The resulting distribution shows less agreement with Benford’s law. The obtained results suggest that Benford’s law may find an interesting application in the evaluation of the detection efficiency of a given lightning location network.

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Diendorfer G., H. Pichler, M. Mair:
Cumulative charge transfer by upward lightning to the Gaisberg Tower

International Conference on Grounding and Earthing and 4th International Conference on Lightning Physics and Effects (GROUND/LPE), Salvador, Brazil, 2010

Tall structures such as towers or wind turbines are able to initiate upward lightning. This type of discharges typically starts with an initial stage (IS) that may or may not be followed by one or more downward leader/upward return stroke sequences. At the instrumented Gaisberg Tower (GBT) we have measured significant amounts of charge up to 546 As per flash. This values clearly exceeds the 300 As specified in the IEC 62305-1 standard for Lightning Protection Level I (LPL I). Up to 3 735 As were transferred to ground by 22 flashes during a single storm within 25 minutes. During a 10 years period we determined at the GBT an annual average charge transfer of 4 100 As.

Highest charge transfer is observed in the months March and November, respectively, at the beginning and end of the winter season in Austria indicating certain similarities with so-called winter lightning typically observed in Japan.

At the GBT the maximum accumulated charge transfer in one year was 8 888 As corresponding to a total melted volume of 35 cm3, 48 cm3 and 100 cm3 for Steel, Copper and Aluminum, respectively at the lightning channel attachment point.

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Diendorfer G., W. Schulz, H. Pichler:
Zero-crossing time and pulse width of radiated fields from lightning to elevated objects

International Conference on Grounding and Earthing and 4th International Conference on Lightning Physics and Effects (GROUND/LPE), Salvador, Brazil, 2010

In this paper we present the analysis of the width values reported by lightning location system (LLS) sensor for three different subsets of lightning events. The three
data sub-sets are (1) lightning to the Gaisberg Tower (GBT), (2) lightning located near the GBT and (3) lightning located near Vienna where correlated video images are available. Median width values for these three data sets are 11 μs, 20 μs and 27 μs, respectively. The sensor reported width of the field pulses from lightning to the GBT is significantly smaller then the sensor reported field pulse width from lightning to ground near the GBT and near Vienna, respectively. This is in agreement with the observations of Pichler et al. [1] reporting peak-to-zero values of electric field pulses radiated by GBT strokes being significantly shorter than typically zero crossing times observed in natural cloud to ground lightning.

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Saba, M. M. F., W. Schulz, T. A. Warner, L. Z. S. Campos, C. Schumann, E. P. Krider, K. L. Cummins, and R. E. Orville:
High-speed video observations of positive lightning flashes to ground

Journal of Geophysical Research: Atmospheres, Vol. 115, D24201, doi:10.1029/2010JD014330, 2010

Although positive lightning flashes to ground are not as frequent as negative flashes, their large amplitudes and destructive characteristics make understanding their parameters an important issue. This study summarizes the characteristics of 103 positive cloud-to-ground (+CG) flashes that have been recorded using high-speed video cameras (up to 11,800 frames per second) in three countries together with time-correlated data provided by lightning location systems (LLS). A large fraction of the +CG flashes (81%) produced just a single stroke, and the average multiplicity was 1.2 strokes per flash. All the subsequent strokes in multiple-stroke +CG flashes created a new ground termination except one. The geometric mean of 21 interstroke time intervals was 94 ms, which is about 1.5 times larger than the average interstroke interval in negative CG flashes (∼60 ms); 75% of the +CG flashes contained at least one long continuing current (LCC) ≥ 40 ms, and this percentage is significantly larger than in the negative flashes that produce LCCs (approximately 30%). The median estimated peak current (Ip) for 116 positive strokes that created new ground terminations was 39.4 kA. Positive strokes with a large Ip were usually followed by a LCC, and both of these parameters are threats in lightning protection. The characteristics presented here include the multiplicities of strokes and ground contacts, the percentage of single-stroke flashes, the average interstroke time interval, the durations of the continuing current, and the distributions of Ip, the total flash durations, and the 2-D leader speeds.

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