2015

Diendorfer G.:
On the Risk of Upward Lightning Initiated from Wind Turbines

International Conference on Environment and Electrical Engineering (EEEIC), 2015

In recent years the number of wind turbines installed in Europe and other continents has increase dramatically. Appropriate lightning protection is required in order to avoid costly replacements of lightning damaged turbine blades, components of the electronic control system, and/or temporary loss of energy production. Depending on local site conditions elevated objects with heights of 100 m and more can frequently initiate upward lightning. From the 100 m high and instrumented radio tower on Gaisberg in Austria more than 50 flashes per year are initiated and measured. Also lightning location systems or video studies in Japan [1], [2] or in the US [3] show frequent occurrence of lightning initiated from wind turbines, especially during cold season. Up to now no reliable method exists to estimate the expected frequency of upward lightning for a given structure and location. About half of the flashes observed at the GBT are of ICCOnly type. Unfortunately this type of discharge is not detected by lightning location systems as its current waveform does not show any fast rising and high peak current pulses as typical for first or subsequent return strokes in downward lightning (cloud-toground). Nevertheless some of this ICCOnly type discharges transferred the highest amount of charge, exceeding the 300 C specified in IEC 62305 for lightning protection level LPL I.

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Defer E., J.-P. Pinty, S. Coquillat, J.M. Martin, S. Prieur, S. Soula, E. Richard, W. Rison, P.R. Krehbiel, R.J. Thomas, D. Rodeheffer, C. Vergeiner, F. Malaterre, S. Pedeboy, W. Schulz, T. Farges, L.J. Gallin, P. Ortéga, J.-F. Ribaud, G. Anderson, H.-D.

Atmospheric Measurement Techniques, 8, 649-669, doi:10.5194/amt-8-649-2015, 2015

The PEACH project (Projet en Electricité Atmosphérique pour la Campagne HyMeX – the Atmospheric Electricity Project of the HyMeX Program) is the atmospheric electricity component of the Hydrology cycle in the Mediterranean Experiment (HyMeX) experiment and is dedicated to the observation of both lightning activity and electrical state of continental and maritime thunderstorms in the area of the Mediterranean Sea. During the HyMeX SOP1(Special Observation Period) from 5 September to 6 November 2012, four European operational lightning locating systems (ATDnet, EUCLID, LINET, ZEUS) and the HyMeX lightning mapping array network (HyLMA) were used to locate and characterize the lightning activity over the northwestern Mediterranean at flash, storm and regional scales. Additional research instruments like slow antennas, video cameras, microbarometer and microphone arrays were also operated. All these observations in conjunction with

operational/research ground-based and airborne radars, rain gauges and in situ microphysical records are aimed at characterizing and understanding electrically active and highly precipitating events over southeastern France that often lead to severe flash floods. Simulations performed with cloud resolving models like Meso-NH and Weather Research and Forecasting are used to interpret the results and to investigate further the links between dynamics, microphysics, electrification and lightning occurrence. Herein we present an overview of the PEACH project and its different instruments.

Examples are discussed to illustrate the comprehensive and unique lightning data set, from radio frequency to acoustics, collected during the SOP1 for lightning phenomenology understanding, instrumentation validation, storm characterization and modeling.

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Nag A., M.J. Murphy, W. Schulz, K.L. Cummins:
Lightning Locating Systems: Insights on Characteristics and Validation Techniques

Earth and Space Science, 2, 65–93. doi: 10.1002/2014EA000051, 2015

Ground-based and satellite-based lightning locating systems are the most common ways to detect and geolocate lightning. Depending upon the frequency range of operation, LLSs may report a variety of processes and characteristics associated with lightning flashes including channel formation, leader pulses, cloud-to-ground return strokes, M-components, ICC pulses, cloud lightning pulses, location, duration, peak current, peak radiated power and energy, and full spatial extent of channels. Lightning data from different types of LLSs often provide complementary information about thunderstorms. For all the applications of lightning data, it is critical to understand the information that is provided by various lightning locating systems in order to interpret it correctly and make the best use of it. In this study, we summarize the various methods to geolocate lightning, both ground-based and satellite-based, and discuss the characteristics of lightning data available from various sources. The performance characteristics of lightning locating systems are determined by their ability to geolocate lightning events accurately with high detection efficiency and with low false detections and report various features of lightning correctly. Different methods or a combination of methods may be used to validate the performance characteristics of different types of lightning locating systems. We examine these methods and their applicability in validating the performance characteristics of different LLS types.

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Zhou H., V.A. Rakov, G. Diendorfer, R. Thottappillil, H. Pichler, M. Mair:
A study of different modes of charge transfer to ground in upward lightning

Journal of Atmospheric and Solar-Terrestrial Physics (JASP), 2015

We examine properties of pulses superimposed on the slowly varying initial-stage current in upward flashes initiated from the Gaisberg Tower (GBT), Austria, based on simultaneous measurements of currents, electric field changes, and high-speed video images. These pulses, often referred to as initial continuous current (ICC) pulses, are associated with the M-component mode of charge transfer to ground, if only one branch of the upward lightning channel is active. However, due to multiple branches formed by an upward leader from the tall tower, ICC pulses are often associated with a downward leader/return-stroke process in a decayed (new) channel branch that is connected to another, continuous current carrying channel, with the connection point being some tens to a few hundreds of meters of the tower top. We call this scenario mixed mode of charge transfer to ground, which optically appears as a re-illuminated (previously luminous) or newly illuminated branch connecting to the already luminous channel attached to the tower. If the connection point were a kilometer or more above the tower top (inside the cloud), the resultant ICC pulse measured at the tower top would appear as a “classical” M component, and if it were very close to the tower top (say, within a few meters), the ICC pulse would be characteristic of a return stroke. In contrast to tower-initiated lightning, ICC pulses in rocket-triggered lightning (at least in Florida and China), usually involve only one channel below the cloud base and hence are associated predominantly with the M-component mode of charge transfer to ground. In our data set, ICC pulses associated with the mixed mode of charge transfer to ground exhibit shorter risetimes, larger peaks, and shorter half-peak widths than “classical” M-components, as previously reported for lightning initiated from tall objects by Miki et al. [2005]. We found that the mixed mode of charge transfer to ground can also occur in M-components following return strokes in upward lightning.

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Diendorfer G., H. Pichler, W. Schulz:
LLS Detection of Upward Initiated Lightning Flashes

9th Asia-Pacific International Conference on Lightning (APL), Nagoya, Japan, 2015

Upward initiated lightning from tall structures has become a major topic in lightning research and lightning protection. Wind turbines of heights of 150 m and more are frequently initiating upward lightning and these discharges may cause severe damage. Upward initiated lightning shows a wide variety of waveform characteristics and does often not contain any return strokes. Lightning location systems (LLS), such as the EUCLID network, are typically detecting return strokes and therefore performance of LLS in detecting upward lightning is very different from the performance to detect downward lightning. Analyzing the lightning data collected at the Gaisberg Tower (GBT) in Austria from 2000 – 2013 we determine a flash detection efficiency (DE) of 43 %. Different from natural CG, lightning where it is mostly the small peak current events that are not located, the low DE of upward lightning is determined by the occurrence of ICCOnly type discharges which are not detected at all. Some of these not located ICCOnly discharges showed a total charge transfer exceeding 300 As and in case of wind turbines those flashes have certainly the potential for severed blade damage. As a result of the significantly shorter peak-to-zero times of the radiated fields from return strokes to the GBT 31% of these return strokes were classified as IC discharges by the LLS.

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Schulz W.:
Location Accuracy Improvements of the Austrian Lightning Location System During the Last 10 Years

9th Asia-Pacific International Conference on Lightning (APL), Nagoya, Japan, 2015

The Austrian lightning location system ALDIS (Austrian Lightning Detection and Information System) has been in operation for more than 20 years. During this time the system has almost continuously been upgraded and improved. This paper gives an overview of the used methods to evaluate the location accuracy, the main improvements in the network during the last 10 years and their resulting impact on the location accuracy of the network.

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Kohlmann H., W. Schulz, H. Pichler:
Compensation of Integrator Time Constants for Electric Field Measurements

International Symposium on Lightning Protection (XIII SIPDA), Balneário Camboriú, Brazil, 2015

Rubinstein et al. [1] presented the measurement of the electric field strength during lightning discharge with analogue integrators as amplifiers and their numerical correction of the time constant that is needed by means of stability of the integrator. We have extended his work by incorporating the antenna characteristic into the system equations. In this paper we focus on the compensation of the integrator time constant (Eq. (13), [1]). We also defined the parameter ka which was introduced in Eq. (6) of [1]. Further, we analyzed and present results of that compensation method for time synchronized E-field measurements with two different integrators, so called E-slow and E-fast, recorded in Sao Paulo City on March 1st, 2014. In this context we discovered the importance of offset errors that exist. It will be discussed, why the offset of the system has a large influence while using the method of compensation and a simple approach for handling the offset will be presented. Additionally we show that this compensation method can be used to determine continuing currents by applying this method to fast E-fields. To verify this we used a sample of recorded current and fast E-field at Gaisberg Tower in Salzburg, Austria. The advantage of the compensation method for E-fast in comparison to an almost ideal integrator (E-slow) regarding the gain and quantization noise will be mentioned in the conclusion. The Appendix A contains the description of the system in the Laplace domain with useful simplifications, and shows the Bode plots.

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Schumann C., M.M.F. Saba, F.M.A. Da Silva , G. Diendorfer, W. Schulz,
T.A. Warner:
Analysis of terrain and atmospheric conditions for upward flashes in Sao Paulo-Brazil

International Symposium on Lightning Protection (XIII SIPDA), Balneário Camboriú, Brazil, 2015

Since 2012 upward flashes have been observed in two locations in Sao Paulo City: Jaraguá Peak and Paulista Avenue. TV and Radio towers are located on the top of a steep hill called Jaraguá Peak. Paulista Avenue is a very busy complex of several buildings with tall towers on top. Upward flashes were registered from towers for both locations. For one of the events we observed upward leaders from both locations even though they are 11 kilometers apart. In order to understand which meteorological and terrain conditions are propitious for upward leader initiation, 83 flashes were analyzed and the results are presented in this paper. An analysis of the mountain profile and a comparison between Jaraguá Peak and other towers around the world used in lightning incidence studies is shown in this paper. The analysis is done by using 3 methods to calculate the effective height of the towers proposed by the literature.

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