ICAE International Commission on Atmospheric Electricity


ICAE 2003 Versailles

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Thursday 11th June

 


10:30

Session C2 Physics of Lightning II


   
11:00 V. Kodali, V. A. Rakov, M. A. Uman, K. J. Rambo, G. H. Schnetzer, J. Schoene, and D. E. Crawford
Lightning Properties Inferred from Measurements of Very Close Electric Fields
   
11:15

M. Miki, T. Shindo, V. A. Rakov, M. A. Uman, K. J. Rambo, G. H. Schnetzer, G. Diendorfer, M. Mair, F. Heidler, W. Zischank, and R. Thotappillil
Characterization of pulses superimposed on the initial continuous current of upward lightning

   
11:30 O. Pinto Jr., I. R. C. A. Pinto, and M. M. F.Saba
Lightning research in Brazil: recent results on Direct Measurements
   
11:45 M. A. Stanley, A. R. Jacobson, and X-M. Shao
The VHF Power Spectrum of Lightning

 


Lightning Properties Inferred from Measurements of Very Close Electric Fields
 

V. Kodali, V.A. Rakov, M.A. Uman, K.J. Rambo, G.H. Schnetzer, J. Schoene, D.E. Crawford
Department of Electrical and Computer Engineering, University of Florida, Gainesville

 

Close electric field and channel-base current measurements for rocket-triggered lightning (i.e., Rakov et al. 1998) are used to infer various properties of lightning discharges, including

  • leader and return-stroke charge densities;
  • leader and return-stroke propagation speeds;
  • leader potential;
  • leader charge near ground apparently left unneutralized by the return stroke.

Correlations between the inferred quantities are discussed. Although the analysis is based on simple models, the results are generally similar to those obtained from independent measurements and/or expected from theoretical considerations.

The measurements were made at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida. Triggered-lightning strokes are similar to subsequent strokes in natural lightning. Therefore, the results presented in this paper are likely to apply to subsequent strokes in natural lightning.

Additionally, electric and magnetic fields of the initial current variation occurring during the initial stage (e.g., Wang et al. 1999b) of rocket-triggered lightning are examined. It is inferred that the initial current variation might be produced by a mini leader/return stroke sequence bridging the gap of some hundreds of meters in length resulted from the explosion of the triggering wire. The wire explodes when the current of the upward positive leader extending from the upper end of grounded triggering wire exceeds some hundreds of amperes.

References:

Rakov, V.A., Uman, M.A., Rambo, K.J., Fernandez, M.I., Fisher, R.J., Schnetzer, G.H., Thottappillil, R., Eybert-Berard, A., Berlandis, J.P., Lalande, P., Bonamy, A., Laroche, P., and Bondiou-Clergerie, A. 1998. New Insights into Lightning Processes Gained from Triggered-Lightning Experiments in Florida and Alabama. J. Geophys. Res., 103, 14,117-14,130.
Wang, D., Rakov, V.A., Uman, M.A., Fernandez, M.I., Rambo, K.J., Schnetzer, G.H., and Fisher, R.J. 1999b. Characterization of the Initial Stage of Negative Rocket-Triggered Lightning. J. Geophys. Res., 104, 4213-4222.

 

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Characterization of pulses superimposed on the initial continuous current of upward lightning
 

M. Miki, T. Shindo, V. A. Rakov, M. A. Uman, K. J. Rambo, G. H. Schnetzer, G. Diendorfer, M. Mair, F. Heidler, W. Zischank, R. Thottappillil, D. Wang

 

We compare the characteristics of initial continuous current pulses (ICC pulses) in natural upward lightning as observed on (1) the Gaisberg tower (100 m, Austria)[1], (2) the Peissenberg tower (160 m, Germany)[2], and (3) the Fukui chimney (200 m, Japan)[3] with their counterparts in rocket-triggered lightning in Florida [4]. All lightning events analyzed here effectively transported negative charge to ground. The geometric mean values of the characteristics of the ICC pulses, magnitude (P), duration (T), risetime (R), and half-peak-width (H) for rocket-triggered lightning (P=113 A, T=2.59 ms, R=464 ms, H=943 ms) are different from their counterparts for Gaisberg tower flashes (P=>377 A, T=1.20 ms, R=<110 ms, H=276 ms), Peissenberg tower flashes (P=512 A, T=0.833 ms, R=60.9 ms, H=153 ms), and Fukui chimney flashes (P=781 A, T=0.514 ms, R=44.2 ms, H=141 ms). The characteristics of lightning initiated by the upward leader from the towers (Gaisberg, Peissenberg, Fukui) are similar within a factor of two. Further, we examine correlations between the characteristics of ICC pulses. The correlations between magnitude and time characteristics (duration, risetime, Half peak width) were very weak in all upward lightning data sets. However, the correlation (Coefficient=0.32) between risetime and continuous current level in rocket-triggered lightning was stronger than those of other upward lightning (Gaisberg =0.09, Peissenbeg =0.04, Fukui=0.08). From these comparisons, we conclude that ICC pulses of lightning initiated from the towers are different from those of the rocket-triggered lightning. Possible reasons for the disparity will be discussed.

References:

[1]Diendorfer G., et al., "Lightning Current Measurements in Austria -Experimental Setup and Results" 25th ICLP(Rhodes), 1.14, pp. 44-47, 2000

[2]Heidler F., et al., "Statistics of Lightning Current Parameters and Related Nearby Magnetic Field Measured at the Peissenberg Tower" 25th ICLP(Rhodes), 1.18, pp. 78-83, 2000

[3]Asakawa A., et al., "Two type of Lightning Discharge to a High Stack on the Coast of the Sea of Japan in Winter" IEEE Trans. on Power Delivery, 12, pp. 1222-1231, 1997

[4]Rakov V. A., et al., "New Insights into Lightning Processes Gained from Triggered Lightning Experiments in Florida" J. Geophys. Res., 103, pp. 14117-14130, 1998

 

TopFull program for C2 Session
 

Lightning Research in Brazil: recent results
1. Direct Measurements
 

O. Pinto Jr., I.R.C.A. Pinto, M.M.F. Saba, N.N. Solorzano and D. Guedes
Brazilian Institute of Space Research (INPE) - Brazil
(Phone: 55-12-39456777, Fax: 55-12-39456810, E-mail: osmar@dge.inpe.br)

 

The lightning research in Brazil is reviewed based on recent direct measurements of natural and triggered lightning captured in the Morro do Cachimbo field station, located near Belo Horizonte, state of Minas Gerais, and in the International Center for Triggering Lightning, located in Cachoeira Paulista, state of São Paulo, both in the Southeast part of the country. Their characteristics (multiplicity and peak current) are revised and compared with similar data obtained outside the tropics by other instrumented towers in Europe, Japan, and Canada and by a similar triggering lightning facility in Florida, United States. The influence of the different techniques used in these measurements on the results are also discussed. The comparison of the multiplicity and peak current measurements in the Morro do Cachimbo station with other similar measurements was done considering the different current threeshold adopted and the different location of the current sensor in the tower. The comparison of the triggered lightning characteristics, in turn, was done considering the different triggered methods used.

 

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The VHS Power Spectrum of Lightning
 

Mark A. Stanley, Abram R. Jacobson, and Xuan-Min Shao
Space and Atmospheric Sciences, NIS-1, MS D466
Los Alamos National Laboratory
Los Alamos, NM 87545
(505) 667-8353

 

VHF emissions from lightning have been used with great success to map lightning regionally with ground-based sensors as well as detect lightning globally from orbit. Several earlier studies have indicated that the VHF power from lightning falls off roughly as the inverse square of frequency. However, very little is known about how this statistical average spectral behavior varies among the different discharge processes and even less is known about the physical mechanisms responsible for the emissions.

The FORTE satellite was used to examine the VHF spectrum of lightning primarily in the 26-48 MHz region. Numerical Electromagnetics Code (NEC) software was used to theoretically model the antenna response of FORTE's log-periodic antenna as both a function of frequency and angle. The NEC model accurately predicted the locations in frequency of dropouts in sensitivity and also showed a relatively flat response outside of these regions. The frequencies with a predicted flat response were used to characterize the power spectral behavior of lightning. Some significant departures from the inverse square behavior were found, particularly for some cloud-to-ground attachment and narrow bipolar events (NBEs). Dart-leader attachment processes were characterized by a much softer spectrum (power falls off much faster with increasing frequency) than inverse squared while several NBEs were found which had a harder spectrum. These spectral characteristics will be compared with the latest theoretical models of leader advancement and attachment processes and some inferences will be drawn about VHF emission mechanisms.

 

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