2005

Schulz W., B. Lackenbauer, H. Pichler, G. Diendorfer:
LLS data and correlated continuous E-Field measurements

VIII International Symposium on Lightning Protection (SIPDA), Sao Paulo, Brazil, 2005

In 2003 we developed a PC based and GPS synchronized field measurement system which is able to measure and record electric field data continuously. This field measurement system is based on a 12 bit digitizing board operating with a sampling rate of 5 MS/s. The board allows to record a maximum of two channels at the same time. Once every second the field data are stored on the hard disc of the PC. Depending on the number of recorded channels (one or two) the size of the "one-second" file is 10MB or 20MB, respectively. Such a continuous and GPS synchronized field measurement system has some important advantages compared to a triggered system. There is no trigger threshold and no dead time and therefore we basically do not miss any events. In this paper we show some preliminary results of a first measurement campaign in summer 2004. We show results from the amplitude ratios between first and subsequent strokes [Diendorfer et al., 1998] and we give some examples of erroneously classified bipolar flashes [Schulz and Diendorfer, 2003].

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Schulz W., K. Cummins, G. Diendorfer, M. Dorninger:
Cloud-to-ground Lightning in Austria: A 10-year Study using Data from a Lightning Location System

Journal of Geophysical Research, Vol. 110, 2005

In this paper we present lightning statistics for more than three million cloud-to-ground (CG) flashes located during the 10 year operation period 1992-2001 of the Austrian lightning location system (LLS) called ALDIS (Austrian Lightning Detection and Information System). Like a majority of other lightning systems operated worldwide, ALDIS underwent configuration changes and continuous performance improvement. Since these changes can alter the lightning statistics, we also relate the variation of the individual lightning parameters during the period of operation to changes in ALDIS configuration and performance. This analysis should be useful to other network operators and data users. Flash densities in Austria are normally between 0.5 and 4 flashes km-2 yr-1 depending on terrain. Flash densities higher than 4 flashes km-2 yr-1 are typically related to mountain tops or high towers on elevated sites. Flashes are classified as negative, positive or bipolar (both negative and positive strokes comprising the flash). 17% of the flashes were classified as positive (90% single strokes and 10% multistrokes), and 2.3% of the total number of flashes were bipolar. 50% of the positive multiple-stroke flashes were bipolar flashes with positive first stroke -- this influences the positive flash multiplicity and interstroke interval statistics. Compared to many other networks, the ALDIS network reports much lower median negative peak currents. For 2001, the median first-stroke peak current for negative flashes was 10kA. We show that even when using the same configuration parameter as used in the U.S. National Lightning Detection Network (NLDN), the median first-stroke peak current in an NLDN region with similar climate is about 30% higher than in Austria. Some of this difference is likely due to better detection efficiency (DE) in the ALDIS network. Estimated multiplicity of negative flashes for the 10-year period is affected by the algorithm that groups strokes into flashes, as well as the improved DE of the network as a result of the integration of ALDIS into the European LLS (EUCLID). This performance improvement also resulted in a higher number of single stroke flashes. Interstroke interval and median first-stroke peak current show a clear correlation with multiplicity for negative flashes, irrespective of DE. Negative flashes with higher multiplicity show smaller average interstroke intervals and larger first stroke median peak currents. No correlation between interstroke interval and stroke order was found. On average, regions with higher flash density show slightly higher flash multiplicity.

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Miki M., V. A. Rakov, T. Shindo, G. Diendorfer, M. Mair, F. Heidler, W. Zischank, M. A. Uman, R. Thottappillil, D. Wang:
Initial stage in lightning initiated from tall objects and in rockettriggered lightning

Journal of Geophysical Research, Vol. 110, 2005

We examine the characteristics of the initial stage (IS) in object-initiated lightning derived from current measurements on the Gaisberg tower (100 m, Austria), the Peissenberg tower (160 m, Germany), and the Fukui chimney (200 m, Japan) and their counterparts in rocket-triggered lightning in Florida. All lightning events analyzed here effectively transported negative charge to ground. For rocket-triggered lightning the geometric mean (GM) values of the three overall characteristics of the initial stage, duration, charge transfer, and average current, are similar to their counterparts for the Gaisberg tower flashes and the Peissenberg tower flashes, while the Fukui chimney flashes are characterized by a shorter GM IS duration and a larger average current. The GM IS charge transfer for the Fukui chimney flashes is similar to that in the other three data sets. The GM values of the action integral differ considerably among the four data sets, with the Fukui action integral being the largest. The observed differences in the IS duration between the Fukui data set and all other data considered here are probably related to the differences in the lower current limits, while the differences in the action integral cannot be explained by the instrumental effects only. There appear to be two types of initial stage in upward lightning. The first type exhibits pulsations (ringing) during the initial portion of the IS, and the second type does not. The occurrence of these types of IS appears to depend on geographical location. The characteristics of pulses superimposed on the initial continuous current (ICC pulses) in object-initiated (Gaisberg, Peissenberg, and Fukui) lightning are similar within a factor of 2 but differ more significantly from their
counterparts in rocket-triggered lightning. Specifically, the ICC pulses in object-initiated lightning exhibit larger peaks, shorter risetimes, and shorter half-peak widths than do the ICC pulses in rocket-triggered lightning.

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Heidler F., G. Diendorfer, W. Zischank:
Examples of trees severely destructed by lightning

International Conference on Lightning and Static Electricity (ICOLSE), Seattle, Washington, 2005

When lightning strikes a tree, the lightning current commonly flows along the trunk to ground or it is diverted to the branches, from where it jumps over to ground. The current flow along the trunk normally damages the bark, which is a strong indication that most of the lightning current flows at the surface of the trunk. In the paper we present two examples where obviously the lightning currents entered the trunk. The currents flowing through the trunks had so high amplitudes and specific energies (? i2 dt), that the trunk was completely destroyed. In April 2000, a very strong destruction of a fir occurred in a forest in the South of Germany about 100 km away from Munich. The struck fir was about 32 m high and the diameter at the bottom was greater than 60 cm. The fir splintered into three major fragments, where each of them was estimated to have a weight in the order of half a ton. The explosion was so severe that the major parts of the tree were blasted away more than 10 m from the remnant stub. Further, lots of smaller fragments with weights up to more than 100 kg were found in the surrounding area up to about 80 m distance from the tree. Due to the extent of the destruction it is concluded that parts of the trunk really exploded. At more than 10 surrounding trees large areas of the bark were damaged obviously by fragments hitting them with high speed. The data from the German lightning detection system (Siemens, BLIDS) revealed, that the fir was probably struck by a positive cloud-toground lightning having a current peak value of roughly 50 kA. Similar destructions occurred in Austria, where also a tree was found which also obviously exploded. With the Austrian lightning detection system (ALDIS) the lightning strike could successfully be detected. Also in this case the tree was obviously struck by a positive cloud-to-ground lightning having a current peak value of about 100 kA.

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Schulz W., G. Diendorfer:
Qualitätsverbesserungen des deutschen Blitzortungssystems

Elektrotechnik und Automation (ETZ) 2, 2005

Jahres 2000 erkennbar. 1999 wurden zusätzlich sechs Sensoren in den Benelux-Ländern und drei Sensoren in Polen in das Netzwerk integriert. Wegen Problemen mit dem Ortungsalgorithmus, wenn große Bereiche ausschließlich mit LPATS-Sensoren abgedeckt werden, Das deutsche Blitzortungssystem BLIDS (Blitzinformationsdienst von Siemens) ist seit mehr als elf Jahren in Betrieb. Während dieser Zeit haben mehrere Änderungen im Bereich der Hard- und Software stattgefunden, die zu einer Qualitätsverbesserung des Ortungssystems geführt haben. In diesem Beitrag zeigen wir, welchen Effekt diese Leistungssteigerungen auf verschiedene Blitzparameter während der einzelnen Jahre haben.

siehe auch Jahrbuch der Elektrotechnik 2006, VDE Verlag, Band 25.

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Diendorfer G., H. Pichler, M. Mair:
Characteristics of positive upward lightning measured on an instrumented tower

Geophysical Research Abstracts, Vol. 7, 10175, 2005

Lightning to an instrumented tower (height 100 m) on Gaisberg, near to the city of Salzburg, is measured since 1998. From 2000-2003 we have recorded a total of 242 flashes to the instrumented tower. Lightning current is measured by digitizing 20MS/s) the output signal of a 0.25mOhm current viewing resistor (shunt) over a sampling time of 800 ms. The fast majority (236 out of 242) of the recorded flashes were upward initiated, as typical for elevated objects. 9 flashes lowered positive charge to ground and have therefore been initiated by upward negative leaders from the tower top. All these 9 positive flashes occurred during cold season or winter time (September - March). Total flash duration is in the range from 6 to 190 ms (mean 70.8 ms) and total charge transfer is in the range from 20 to 376 As (mean 130 As). Typically the observed overall current waveform exhibits a front section with significant pulsing structure lasting for about 2.1 ms (median).Recorded waveforms are very similar to measured currents of triggered winter lightning in Japan (Yoda et al., 1997, Nakamura et al., 1997). We have analyzed in detail the pulsing front section of the current waveforms. They show 25 to 89 (mean 60) current pulses with pulse duration of 27 to 44µs (mean 34 µs). D The pulses are superimposed on a steadily increasing continuous current. The pulse duration is comparable to the inter-step intervals of 30 to 50 µs determined optically for negative upward leaders observed at Mont San Salvatore (see Rakov and Uman, 2003). Mean values of the peak current of these leader pulses are in the range of 1.6 to 13.7 kA. For each of the 9 flashes we have determined for the distinct pulses a mean charge transfer in the range from 0.013 C to 0.321 C. Wada et al. (2002) measured for the same type of lighting to a 200 m high chimney in Japan a leader propagation speed of 6.106 m/s. Assuming a speed of 6.106 m/s a pulse-duration of 34 µs corresponds to a step length of 204 m, which is in the same range as the optically observed step lengths reported by Wada et al (2002). For three distinct steps Wada et al. (2002) determined a two dimensional length of 45m, 118m and 311m.

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