ICAE International Commission on Atmospheric Electricity


ICAE 2003 Versailles

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Benjamin Franklin
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Thursday 11th June

 


16:00

Session C4 Physics of Lightning IV (poster)


   
  G. Baffou, E. P. Krider, N. D. Murray and J. C. Willett
dE/dt and E waveforms radiated by leader steps just before the onset of first return strokes striking seawater
   
 

W. H. Beasley, C. M. M. Noble, T. E. Light, D. M. Suszcynsky and B. C. Edgar
Coincident Observations of lightning by Ground-Based and Satellite-Borne Location and Mapping Systems: inferences for Lightning Physics

   
  A-L.Brasseur, P.Laroche, C.Thèry
A New Lightning NOx Production Parameterization
   
  E. Defer, P. Laroche , J. E. Dye and W. Skamarock
Use of total lightning lengths to estimate NOx Production in a Colorado Storm
   
A. K. Erickson, P. R. Krehbiel and W. K. Hocking
Three-Dimensional Imaging of Lightning Channels using a 35 MHz Interferometric Radar: Preliminary Results
   
  T. Fehr and N. Dotzek
Lightning Activity and Bulk Microphysical Properties
   
  L. Grcev, F. Rachidi and V. Rakov
Comparison of Electromagnetic Models of the Lightning Return Stroke Using Current and Voltage Sources
   
  J. Harlin, T. Hamlin, P. Krehbiel, R. Thomas, and W. Rison
Using the NMIMT LMA to Determine Which Model of Lightning Initiation Fits Best with Measured Results
   
  M. J. Heavner, D. M. Suszcynsky, and D. A Smith
LF/VLF Intracloud Waveform Classification
   
  D. I. Iudin, V. Y. Trakhtengerts, A. Grigoryev, and M. Hayakawa
Electric charge fractal transport and electromagnetic high frequency radiation on the lightning discharge preliminary stage
   
  J. Jerauld, M. A. Uman, V. A. Rakov, K. J. Rambo, D. M. Jordan, and G. H. Schnetzer
Multiple-Station Measurements of Close Electric and Magnetic Fields and Field Derivatives from Natural Lightning
   
 

W. J. Koshak, R. J. Solakiewicz, R. J. Blakeslee, S. J. Goodman, H. J. Christian, J. M. Hall, J. C. Bailey, E. P. Krider, M. G. Bateman, D. J. Boccippio, D. M. Mach, E. W. McCaul, M. F. Stewart, D. E. Buechler, W. A. Petersen
Error Analyses of the North Alabama Lightning Mapping Array (LMA)

   
  A. K. Kamra and S. D. Pawar
Recovery curves of the lightning discharges initiated from the lower positive charge pocket in thunderstorm
   
  P. Lalande, P. Blanchet, P. Laroche, S. Laik, S. Luque, J.-A. Rouquette, H. Poirot, P.-N. Gineste, F. Hoeppe, A. Ulmann, and P. Dimnet
ALISDAR: an Automatic Lightning System Detection and Recording
   
  O. Mendes Jr., M. O. Domingues, E. E. N. Macau and A. P. dos Santos
Studies on lightning flashes by using fractal analyses and methods of geometrical statistics
   
  O. Mendes Jr., M. O. Domingues, J. C. Thomaz and D. F. da Silva
Analysis of some lightning features based on the numerical stepped leader path simulation
   
  F. J. de Miranda, O. Pinto Jr. and M. M. F. Saba
Advances in electric field and light measurements of lightning in Brazil
   
  J. Montanyà, J. Bergas, and B. Hermoso
Ceptrum application to electrostatic field on lightning prediction
   
  N. D. Murray, E. P. Krider, and J. C. Willett
Multiple Pulses in the Electric Field Derivative, dE/dt, During the Onset of First Return Strokes in Lightning Striking
   
W. Rison, W. P. Winn, and S. J. Hunyady
Initial Results from a Compact, High Time Resolution, Lightning Mapping System
   
M. A. Stanley and M. J. Heavner
Tall structure lightning induced by sprite-producing discharges
   
T. Suzuki, T. Shimura, and K. Michimoto
Design of Lightning Flash Observation and Ranging System
   
R. Thomas, P. Krehbiel, W. Rison, T. Harlin, J. Hamlin and N. Campbell
The LMA Flash Algorithm
   
T. J. Tuomi
IMPACT-SAFIR comparisons in Finland
   
Y. Zhang, P. Krehbiel, T. Hamlin, J. Harlin, R. Thomas and W. Rison
Observations of radiations from airplane during STEPS

 


dE/dt and E Waveforms Radiated by Leader Steps Just Before the Onset of First Return Strokes Striking Seawater
 

Guillaume Baffou,
Department of Physics, Ecole Normale Supérieure de Cachan, Cachan, FRANCE

E. Philip Krider, Natalie D. Murray,
Institute of Atmospheric Physics, University of Arizona, Tucson, AZ 85721, USA

John C. Willett
P.O. Box 41, Garrett Park, MD 20896, USA

 

We have recently re-analyzed the electric field, E, and dE/dt waveforms that are radiated by leader steps just before the onset of the first return stroke in cloud-to-ground lightning striking sea water. The E and dE/dt signatures were digitized using 10 MHz and 100 MHz sampling, respectively, under conditions where the lightning locations were known and there was minimal distortion in the fields due to the effects of ground-wave propagation. The detailed fine-structure of E has been obtained by integrating dE/dt and comparing with E to eliminate offsets. The dE/dt waveforms of steps fall into three broad categories:

1) simple an isolated negative peak that is immediately followed by a positive overshoot [see Figure 1 below],
2) double two simple impulses that occur at almost the same time, and
3) burst a complex cluster of pulses that typically lasts about one microsecond.

In this report, we will show examples of these waveforms, and we will summarize the measured characteristics of both dE/dt and E. An approximate width of the fast-varying portion of the E impulses has been obtained by measuring the times between the negative peak in dE/dt and the peak of the positive overshoot that follows. Among our initial findings are that the widths of 419 steps averaged 94 ns with a standard deviation of 65 ns; the widths of 265 simple waveforms averaged 62 ns with a standard deviation of 15 ns. 51 return strokes were preceded by a clear step impulse in the 12 56;s interval before the onset of the stroke, and in these cases, the interval between the last leader step and the dominant peak of the return stroke averaged 5.8 56;s with a standard deviation of 1.7 56;s.



Figure 1.
Example of the dE/dt and Eint signatures radiated by the last leader step and the first return stroke in a cloud-to-ground flash striking sea water. The leader step preceeds the return stroke by about 5 56;s.

 

TopFull program for C4 Session
 

Coincident Observations of Lightning by Ground-Based and Satellite-Borne Location and Mapping Systems:
Inferences for Lightning Physics
 

William H. Beasley, Cynthia M. M. Noble,
School of Meteorology, University of Oklahoma, Norman, OK 73019

Tess E. Light, David M. Suszcynsky,
Los Alamos National Laboratory, Los Alamos, NM

Bruce C. Edgar
Edgarhorn, Torrance, CA

 

 

During the past 30 years there have been a few opportunities for simultaneous observations of lightning by ground-based and satellite-borne observing systems. For example, in August, 1977, the DMSP/PBE recorded optical emissions from several lightning flashes for which the ground strike points were located by magnetic direction finding within the field of view of the satellite optical detector at the time. More recently, the PhotoDiode Detector (PDD) aboard the FORTE satellite has recorded many waveforms of transient optical signals which have been found to emanate from storms that produced lightning flashes observed by the US National Lightning Detection System, and, on occasion, by VHF lightning-mapping systems such as the LDAR at the NASA Kennedy Space Center and the Lightning Mapping Array operated by New Mexico Institute of Mining and Technology in STEPS 2000. However, there are significant numbers of cases in which either optical emissions or radio-frequency electromagnetic emissions are observed but not both at the same time. We have compared the characteristics of optical emissions recorded onboard satellites with the characteristics of lightning flashes as determined from ground-based observations in order to begin to address questions about similarities and differences in the physical processes that produce the optical and radio frequency signals. We have found that in some cases, VHF radiation source distributions for flashes detected optically from orbit appear to reach a greater maximum altitude, have greater horizontal extent, and last longer than for flashes that are not detected by a satellite optical detector. We investigate factors such as flash characteristics, storm characteristics, and viewing angle which may govern the detectability of visible and vhf radiation to the end of understanding the physical processes responsible for the different emissions.

 

TopFull program for C4 Session
 

Use of total lightning lengths to estimate NOx Production in a Colorado Storm
 

E. Defer, J. E. Dye and W. Skamarock
National Center for Atmospheric Research, MMM, Boulder, Colorado, USA

P. Laroche
Office National d'Etudes et de Recherches Aérospatiales, DMPH, Châtillon, France

E. Defer
now at Institute for Environment Research, National Observatory of Athens, Athens, Greece

 

We derive total components lengths based on the characteristics and angular locations of the VHF radiation detected by an interferometer. The method differentiates between negative leaders and fast negative processes and applies simple relationships from the physics of lightning to deduce the channel lengths of these components for both intra-cloud and cloud-to-ground lightning flashes. The studied storm produced over 5000 flashes with only 83 connecting to ground. The total component length of individual flashes retrieved varied from 0.02 to 474 km with an average value of 19 km. The sum of total channel lengths for all flash components for the 4 1/2 hour storm was estimated at 102,000 km. For flashes with duration >10 ms the length per flash was found to be related to the flash duration but with a lot of variation. The lightning channel lengths deduced from this work are used by Skamarock et al. [2002] to estimate NOx (= NO + NO2) produced by lightning in the 10 July 1996 storm.

 

TopFull program for C4 Session
 

Three-Dimensional Imaging of Lightning Channels using a 35 MHz Interferometric Radar:
Preliminary Results
 

Alan K. Erickson
New Mexico Tech

Paul R. Krehbiel
New Mexico Tech

Wayne K. Hocking
University of Western Ontario

 

Preliminary observations of radar echoes from lightning have been obtained with a low-frequency all-sky radar. The radar, a commercially available SKiYMET interferometric system designed for meteor studies, operates at 35.24 MHz (8.5 m wavelength) and transmits an adjustable-length pulse into a low gain, semi-omnidirectional antenna. The radar echoes are received using a five-element interferometric antenna array having 2.0-lambda and 2.5-lambda baselines along both north-south and east-west axes. The lightning data were obtained using uncoded 6 kW pulses at a PRF of 2 kHz, and were recorded to 20 km range. The receiving system detects and locates both the passive lightning emissions as well as the active radar echoes. The active returns are differentiated from the passive emissions by calculating a running coherent average for each range gate and from observed persistence of the lightning echoes. Volumetric images of the lightning echoes are obtained by combining the interferometric direction vectors of the echoes with the echo range. The lightning echoes are observed to last from several milliseconds to 200 ms and are typically preceded by several tens of milliseconds of high-power, non-range-correlated RF noise, presumed to be emission from stepped leaders of cloud-to-ground discharges. In many instances, echoes from the same location fade and then reintensify, consistent with channel re-excitation.

 

TopFull program for C4 Session
 

Lightning Activity and Bulk Microphysical Properties
 
Thorsten Fehr and Nikolai Dotzek
Institut für Physik der Atmosphäre, DLR, Oberpfaffenhofen, Germany
 

Parameterization of lightning activity in numerical models using bulk microphysical properties is a cost-efficient alternative to the explicit simulation of charge distribution and lightning initiation in thunderstorms. The retrieval of the microphysical structure in a storm by polarimetric radar analysis combined with observations from lightning detection networks are used to correlate the electrical activity with bulk properties of precipitation particles. The method is applied to three different thunderstorms observed during the EULINOX campaign in 1998. The analysis indicates that both the total and CG activity can be parameterized by bulk microphysical properties a thunderstorm.

 
TopFull program for C4 Session
 

Comparison of Electromagnetic Models of the Lightning Return Stroke Using Current and Voltage Sources
 

Leonid Grcev,
Eindhoven University of Technology, Eindhoven, The Netherlands

Farhad Rachidi,
Swiss Federal Institute of Technology in Lausanne, Lausanne, Switzerland

Vladimir Rakov,
University of Florida, Gainesville, Florida, USA

 

One of the classes of models employed in lightning studies are the so-called electromagnetic models. They are usually based on thin-wire antenna approximation and involve a numerical solution of Maxwell's equations using the Method of Moments to find the current distribution from which electromagnetic fields can be computed. For practical computations existing numerical codes for antenna analysis are typically used. Since such codes are optimized for antenna analysis their application to lightning studies may introduce some problems. One potential problem is related to the use of localized voltage sources in antenna theory models. In fact, the natural choice in lightning return stroke modeling would be a current instead of a voltage source. Indeed, it is the channel-base current that can be measured directly and for which experimental data are available. However, current sources are usually not provided in the existing antenna codes. Further, in antenna theory such voltage sources are usually applied between two closely spaced terminals. On the other hand, in lightning studies there are situations when terminals of the source can be viewed as separated by an infinitely large distance (when the current is injected at a point and/or when potential reference point is at infinity). This paper describes the use of current sources in antenna theory and their implementation in an available thin-wire moment method code. Models using current and voltage sources are compared in terms of the computed channel current as a function of time at different heights above ground and in terms of remote electromagnetic fields.

 

TopFull program for C4 Session
 

Using the NMIMT LMA to Determine Which Model of Lightning Initiation Fits Best with Measured Results
 

J. Harlin, T. Hamlin, P. Krehbiel, R. Thomas, W. Rison
New Mexico Institute of Mining and Technology, Socorro, New Mexico USA

 

The Lightning Mapping Array is a time of arrival system that records the peak RF radiation every 10 to 100 microseconds. The data is then processed and inverted into three dimensional locations, source times and approximate radiated powers. This gives a high resolution image of all lightning within a region, allowing the analysis of individual flashes. Differences in altitude, location and power of the initial points within a flash may indicate which model better describes the initial breakdown. Two of the more popular initiation models are; conventional breakdown from hydrometers, and runaway breakdown from high energy free electrons. The basic concept of conventional breakdown is that water drops deform and the charge on the bottom of the drop enhances the local electric field enough for corona. If enough corona streamers in a given area overlap they can produce a hot plasma channel, a leader. The other model that has been proposed is high energy electrons, mostly cosmic rays, start an electron avalanche which increases the electric field at the head of the avalanche. If the process continues a leader is formed.

A small sub-set of the LMA data have very high radiated source powers, from 100 kW up to 50 MW in the 60-66 MHz passband. This is well above the average LMA event power of 1 W to 10 kW. These energetic events are usually very short, about 10 microseconds, therefore only a single LMA point is recorded. Some of these events have been identified as narrow bi-polar's. These events have been found isolated in time and space as well as being the initial point of a flash.

Overlaying LMA events on duel-polarization radar scans can determine the physical characteristics of the storm as well as where the flash is initiating within the storm. Comparing the LMA sources to measured electric fields can confirm polarity of the breakdown as well as help identify the type of discharge.

 

TopFull program for C4 Session
 

LF/VLF Intracloud Waveform Classification
 

Matthew J Heavner, David M. Suszcynsky, and David A Smith
Space and Atmospheric Sciences, NIS-1, MS D466 Los Alamos National Laboratory Los Alamos, NM 87545 (505) 665-4619

Matt Heavner,
Space and Atmospheric Sciences, TSPA
NIS-1, MS D466
Los Alamos National Laboratory
SM-30, Bikini Atoll Road
Los Alamos, NM 87545
(505) 665-4619
(505) 665-7395
heavner@lanl.gov

 

The Los Alamos Sferic Array network of fast electric-field-change meters has geolocated over seven million lightning events in the United States (primarily near New Mexico and Florida) from 1998 to the present. Previous work has included the automated identification of cloud-to-ground lightning and a specific type of intracloud lightning (narrow bipolar events). We have extended this work to include the identification of general intracloud lightning activity and leader activity preceeding cloud-to-ground discharges.

 

TopFull program for C4 Session
 

Electric charge fractal transport and electromagnetic high frequency radiation on the lightning discharge preliminary stage
 

D.I. Iudin, V.Y. Trakhtengerts,
Institute of Applied Physics, Russian Academy of Science, 46 Ulyanov st., Nizhny Novgorod, 603950, Russia.

A. Grigoryev
Radiophysical Research Institute, 14/25 B. Pecherscaya st., Nizhny Novgorod, 603950, Russia.

M. Hayakawa
The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu Tokyo 182 - 8585, Japan

 

Many systems in nature such as physics, chemistry, biology and even social sciences reveal some common features in their spatial-temporal dynamics, which are now characterized by a common definition as fractal dynamics [1,2]. The thunderstorm cloud (TC) seems to be a bright example of such systems. The source of free energy in a TC is updraft convective flow, which forms multi-flow streams consisting of air molecules, light droplets, ice crystals and heavy hail stones. Interaction of these streams with each other leads to the electrical charging of cloud particles and generation of an electric field [3,4]. A Lightning flash that includes leader progression, return strokes and microdischarges inside of the small-scale cells supply dissipation and sink of free energy in a TC. Two-scale model is developed for electric field in a TC, which includes a large-scale electric field and small-scale electric cells with . Physical basis for these cells can be local corona discharges or dissipative beam-plasma discharge. On the developed stage of thunderstorm short-scale discharges form transport system for large-scale electric charge and supply transition to leader formation. Electric currents of short-scale discharges generate electromagnetic radiation that can be identified with high frequency radiation on the lightning preliminary stage. We find quantitative characteristics of this system: number and duration of short-scale discharges, temporal and spectral characteristics of high frequency radio-emission from this discharges and apply these results to explanation of a lightning preliminary stage. A fractal cellular automaton model of such a scenario is constructed, which considers short-scale discharges as a self-maintaining chain reaction. In this approach an electric charge's transport system is formed as a percolation-like critical phenomenon.

References:

  • P. Bak, How Nature Works (The Science of Self-organized Criticality), Springer-Verlag, New York (1996).
  • E. Feder, Fractals, Plenum Press, New York (1988).
  • D. R. MacGorman and W. D. Rust, The Electrical Nature of Storms, Oxford Univ. Press, Oxford (1998).
  • M. A. Uman, The Lightning Discharge,Int. Geophys. Ser., 39 (1987).

 

TopFull program for C4 Session
 

Multiple-Station Measurements of Close Electric and Magnetic Fields and Field Derivatives from Natural Lightning
 

J. Jerauld, M. A. Uman, V. A. Rakov, K. J. Rambo, D. M. Jordan, and G. H. Schnetzer
Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611

 

We describe an automated multiple-station network for measuring natural-lightning properties. That network began operation during Summer 2002 at the International Center for Lightning Research and Testing at Camp Blanding, Florida, and covers about 1 km2 with 20 time-domain measurements distributed among 11 locations. Measured quantities are the electric field (1 Hz to 5 MHz) at 6 locations, the magnetic field (10 Hz to 4 MHz) at 2 locations, the electric field derivative (a few kHz to 20 MHz) at 4 locations, the magnetic field derivative at 4 locations (a few kHz to 20 MHz), the optical output of the bottom 100 m or so of the channel observed from two locations, and current induced in a 12 m grounded vertical wire on two amplitude levels (DC to 5 MHz). The system is turned on and off by sensing the ambient electric field and is triggered by the signals from the two optical sensors viewing the network from its opposite corners. Video coverage from 4 sites is employed to help determine the location of the lightning within the network and the geometry of the lightning channel. Five to eight ground flashes per year are expected to occur within the network. We present data from one two-stroke positive cloud-to-ground flash and two multiple-stroke negative cloud-to-ground flashes that occurred within the network during Summer 2002.

 

TopFull program for C4 Session
 

Error Analyses of the North Alabama Lightning Mapping Array
(LMA)
 

W. J. Koshak, R. J. Blakeslee, S. J. Goodman, H. J. Christian, J. M. Hall, J. C. Bailey, M. G. Bateman, D. J. Boccippio, D. M. Mach, E. W. McCaul, M. F. Stewart, D. E. Buechler, W. A. Petersen
Global Hydrology & Climate Center, National Space Science & Technology Center, Huntsville, AL 35805

R. J. Solakiewicz
Department of Mathematics & Computer Science, Chicago State University, Chicago, IL 60628

E. P. Krider
Institute of Atmospheric Physics, University of Arizona, Tucson, AZ, 85721

 

Two approaches are used to characterize how accurately the North Alabama Lightning Mapping Array (LMA) is able to locate lightning VHF sources in space and in time. The first method uses a Monte Carlo computer simulation to estimate source retrieval errors. The simulation applies a VHF source retrieval algorithm that was recently developed at the NASA-MSFC and that is similar, but not identical to, the standard New Mexico Tech retrieval algorithm. The second method uses a purely theoretical technique (i.e., chi-squared Curvature Matrix theory) to estimate retrieval errors. Both methods assume that the LMA system has an overall rms timing error of 50ns, but all other possible errors (e.g., multiple sources per retrieval attempt) are neglected. The detailed spatial distributions of retrieval errors are provided. Given that the two methods are completely independent of one another, it is shown that they provide remarkably similar results, except that the chi-squared theory produces larger altitude error estimates than the (more realistic) Monte Carlo simulation.

 

TopFull program for C4 Session
 

Recovery curves of the lightning discharges initiated from the lower positive charge pocket in thunderstorm
 

A K Kamra and S D Pawar
Indian Institute of Tropical Meteorology, Pune, India
kamra@tropmet.res.in

 

Behavior of the recovery curves of the cloud-to-cloud (CC) and cloud-to-ground (CG) discharges initiated from the lower positive charge pocket in a thunderstorm is examined from the measurements of the electric field and Maxwell current made at the ground surface below the thunderstorm. The CC discharges are distinguished from the CG discharges from the Maxwell current measurements. In case of CC discharges, it is observed that the recovery curves are almost linear when the pre-discharge and after-discharge values of the electric field are not strong enough to produce corona at the ground. The recovery curves become exponential if the pre-discharge field is strong enough to produce corona at the ground. However, a step of much slower rate of change of electric field appears in the exponential recovery curve of discharges if both pre- and after- discharge values of electric field can produce corona at the ground. This step is of 4 to 10 s time-duration and always appears when the value of the after-discharge electric field becomes equal to 5-6 kV cm-1. Our observations show that some CG discharges from the lower positive charge pocket trigger a discharge between the main positive and negative charge centers of thunderstorms. From the field recovery curves after such triggered discharges, it is possible to conclude that the rate of charge build-up in the main negative charge center is greater than in the lower positive charge pocket. Charging currents for the lower positive charge pocket and for the negative charge center of main dipole are computed at the point of inflection on recovery curves. Behavior of the recovery curves is interpreted in terms of corona charge released from the ground and the relative rates of charge generation of the main electric dipole and the lower positive charge pocket.

 

TopFull program for C4 Session
 

ALISDAR:
an Automatic Lightning System Detection And Recording
 

P. Lalande, P. Blanchet, P. Laroche,
Onera, France

S. Laik, S. Luque, J.-A. Rouquette, H. Poirot,
EADS-Airbus, France

P.-N. Gineste, F. Hoeppe,
EADS-CCR, France

Ulmann, P. Dimnet,
CEAT, France

 

The EC project FULMEN, achieved in 1999, provides a synthetic study of external and internal threat on aircraft due to lightning. One of the results of the FULMEN program is a database on natural lightning strike to aircraft. During the building of this database, several problems have been pointed out. (1) Most of the lightning scenario and waveforms used in the regulatory document and aircraft certification are based on data coming from natural cloud to ground flashes. Even if this approach is satisfactory from a safety standpoint, it would be very beneficial that the most common in-flight strike scenario be characterized more accurately. Indeed, in-flight experiments have shown that strikes occur at about 3 km and generally result from intra/inter cloud flashes. (2) The data, collected by the company, on lightning strike to airliner do not contain information on the severity of the strike excepted through the damages. (3) The data from in-flight lightning experiment are not enough numerous to provide a representative statistical distribution of the lightning strike to aircraft. This lack of knowledge prevents the regulatory document from improvement (adequacy of laboratory test, lightning pulse sequences, ...) and the lightning protection from optimization.

In the framework of the EC project EM-HAZ (Electromagnetic Hazard), a system is developed to realize in flight lightning detection and characterize the lightning strike to aircraft. ALISDAR (Automatic Lightning Strike Detector And Recorder) is based on electric and magnetic measurements. A prototype has been onboard an Airbus A340 during spring 2001. Two lightning strike to aircraft have been recorded during this in-flight campaign. The electric field variation shows in both of cases that it is the aircraft which triggered the lightning as observed during the Transall in-flight campaign. From the E-field variation, the chronological event involved during a lightning development can be inferred.

Figure 1 : Location of the ALISDAR sensor on the A340-600

 

TopFull program for C4 Session
 

 Studies on lightning flashes by using fractal analyses and methods of geometrical statistics
 

Odim Mendes Jr., Margarete O. Domingues, Elbert E. N. Macau and Ana Paula dos Santos Novaes
Instituto Nacional de Pesquisas Espaciais, P. O. Box 515, 12245-970 São José dos Campos, SP, Brazil

 

Several objects in the Nature present non-regular random shapes, irregular trajectories, complex dynamics, or are randomly scattered in space. Lightning flashes are considered in this category. In this work some fractal analysis techniques and geometrical statistic methods were chosen and presented to be applied in specific features of lightning. The results were interpreted trying to relate them to the electrodynamics properties of the lightning or the atmosphere.

 
TopFull program for C4 Session
 

Analysis of some lightning features based on the numerical stepped leader path simulation
 

Odim Mendes Jr.,
CEA/INPE
Odim@dge.inpe.br

Margarete O. Domingues, José Celso Thomaz,
CPTEC/INPE

Denise Fernandes da Silva
PIBIC-INPE/CNPq

 

A numerical simulation for the stepped leader path in the earth atmosphere has been developed to study the influence of atmospheric parameters on the lightning behavior. This model has been based on the assumption that the leader path follows approximately the gradient of the electric potential (Takagi et al., 1986; Mendes et al., 1996). A perfectly conductor ground surface and a curl-free electric field assumption has been considered (Anderson and Freier, 1969). The influence of the charge configuration (amount of charge and locations, obeying either the dipole model or the continuity current model) and the variations of the atmospheric conductivity (considered according to isotropic model and non-isotropic model, under some adopted profile functions) were studied. The results of simulations showed that different behaviors in the lightning path were reached. In consequence, for instance, different percentages of positive cloud-to-ground flashes in comparison to the total CG flashes were obtained and the occurrence of the long length lightning with safety risk implication was also confirmed. The importance of atmospheric conductivity and space charge in the troposphere on the lightning path were also investigated and discussed.

References:

Anderson, F. J.; Freier, G. D. (1969) Interactions of the thunderstorm with a conducting atmosphere. J. Geophys. Res., 74:53,90-5,396.
Mendes, O. Jr.; Pinto, O. Jr.; Pinto, I. R. C. A.; Chryssafidis (1996) Lightning simulation: the stepped leader paths in the Earth's atmosphere. Proceedings. In "VI Brazilian Plasma Astrophysics Workshop". Rio de Janeiro, Brazil, Brazilian Geophysical Society, 1:150-153.
Takagi, N.; Takeuti, T.; Nakai, T. (1986) On the occurrence of positive ground flashes. J. Geophys. Res., 91:9,0905-9,909.

 

TopFull program for C4 Session
 

Advances in electric field and light measurements of lightning in Brazil
 

F. J. de Miranda*, O. Pinto Jr. and M. M. F. Saba
Instituto Nacional de Pesquisas Espaciais (INPE), Divisão de Geofísica Espacial (DGE),
Av. dos Astronautas, 1758, São José dos Campos, SP, Brazil. CEP 12.227-010

*Corresponding author:
Tel. 00-55-12-3945-6785; fax: 00-55-12-3945-6810; miranda@dge.inpe.br

 

In this paper the first results of interstrokes and inter-K time intervals observations in Brazil by Miranda et al. (2002) in a 37 µs time resolution are presented. They found geometric mean values of 49.6 ms and 12.0 ms for the interstrokes time intervals and the inter-K time intervals respectively. They also found that the interstrokes and inter-K time intervals have no dependence on the return stroke order. The interstrokes time intervals and inter-K time intervals were found to obey a log normal distribution. These results are in agreement with those presented in the literature [Rakov and Uman (1990), Rakov et al. (1990), Thottappillil et al. (1990) and Rakov et al. (1994)]. In addition, a description of a new GPS (Global Positioning System) synchronized apparatus to measure the electric field waveform with a 1.25 µ s time resolution and the light waveform of the lightning discharge with a 4 ns response time light sensor also is done. This apparatus will enable a faithful reproduction and observation of the electric field and light waveforms of lightning discharges. A comparison between future results provided by this apparatus and results provided by SLT (Thunderstorm Location System) also will be possible. It will also enable to investigate the relationship between the electric field and light waveforms. Preliminary data and results will be presented.

References:

Miranda, F. J. de; . Pinto Jr, O.; Saba, M. M. F., 2002. A study of the time interval between return strokes and K-changes of negative cloud-to-ground lightning flashes in Brazil. JATP (in press).
Rakov, V. A; Uman, M. A., 1990. Some properties of negative cloud-to-ground lightning flashes versus stroke order. J. Geophys. Res. 95, 5447-5453.
Rakov, V. A.; Uman, M. A.; Jordan, D. M.; Priore III, C. A., 1990. Ratio of leader to return stroke electric field change for first and subsequent lightning strokes. J. Geophys. Res. 95, 16,579-16,587.
Rakov, V. A.; Uman, M. A.; Thottappillil, R., 1994. Review of lightning properties from electric field and TV observations. J. Geophys. Res. 99, 10,745-10,750.
Thottappillil, R., Rakov, V. A., Uman, M. A. 1990. K and M changes in close lightning ground flashes in Florida. J. Geophys. Res. 95, 18,631-18,640.

 

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Ceptrum application to electrostatic field on lightning prediction
 

J. Montanyà
Electrical Engineering Department, Universitat Politècnica deCatalunya, Barcelona, SPAIN
montanya@ee.upc.es

J. Bergas
Electrical Engineering Department, Universitat Politècnica deCatalunya, Barcelona, SPAIN
bergas@ee.upc.es

B. Hermoso
Electrical and Electronic Engineering Department, Universidad Pública de Navarra, Pamplona, SPAIN
hermoso@si.unavarra.es

 

Electrostatic field can be treated as an output of a complex system. Output of this system can be obtained as the convolution of several inputs.

Fig. 3. Representation of a system.

Where xi(n) corresponds to i-nth input, represented in discrete n times, are convoluted,

(1)

by superposition the output is,

(2)

Where, for each input,

(3)

The electrostatic field signal is very closed to speech signal and problems are very closed, too. One assumption, is that the electric field can be represented as the output of a linear time-varying system whose properties vary slowly with time. Then, considering short segments of the electrostatic field signal, each segment can be modeled by a linear time-invariant system, either by a quasi-periodic impulse train or a random noise signal. Since the impulse response of a linear time-invariant system and the excitation of this system are convoluted, the separation of this components can be made by a homomorphic deconvolution. Then the complex cepstrum is a homomorphic deconvolution method, Rabiner and Shafer (1978).

If the input is a convolution as showed in (1), then the z-transform of the input becomes the product of z-transforms,

(4)

The product logarithm property lets make an approach of the z-transform by,

(5)

Then,

(6)

Schafer, (1978) describes the considerations in determine logarithm so the z-transform is in general a complex quantities.

Computation will be easy by calculation the discrete fourier transformer instead of z-transformer if the input signal have a region of convergence that includes de unit circle.

An interesting case is, in a input composed by a train of impulses, the complex cepstrum will be non zero at integer multiples. So there will be easy identify inputs of this nature.

Under fine weather conditions a frame of electric field and the cepstrum obtained is showed in fig. 1.

Fig.1. Frame of electric field and cepstrum result in fine wheater.

Under storm situations, the cepstrum shows pulses before a quick change on the electric field. Fig. 2 shows one of this situation.

Fig.2. Frame of electric field and cepstrum result under storm conditions.

In storms without discharges, only rain, the cepstrum not present situations as fig. 2. Then the peaks that appears in the cepstrum are an input of the "system" that have the electrostatic field as an output. One assumption is that these inputs can concern to electromagnetic impulse so the peaks appears before the polarity inversion of the field. This is a preliminary assumption, at the moment the important result is the apparition of these inputs.

CONCLUSIONS

Cepstral analysis have been recovered form speech signal processing and applied in an electrical field processing, at the moment preliminary results have been present and seems that an input is identified and acts before the field polarity inversion. More data is need, to identify this input, comparison with lightning location data will be important for this job.

 

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Multiple Pulses in the Electric Field Derivative, dE/dt, During the Onset of First Return Strokes in Lightning Striking
 

Natalie D. Murray and E. Philip Krider
Institute of Atmospheric Physics, The University of Arizona, Tucson, AZ 85721-0081

John C. Willett
P.O. Box 41, Garrett Park, MD, 20896

 

The electric field impulse, E, that is radiated by the first return stroke in cloud-to-ground lightning typically begins with a slow front that lasts for several microseconds, and then there is a fast transition to peak in tens to hundreds of nanoseconds. We have recently re-analyzed 131 dE/dt signatures (digitized using 100 MHz sampling) and the corresponding E waveforms (10 MHz sampling) that were radiated by first strokes striking sea water, under conditions where the lightning locations were known and there was minimal distortion in these fields due to the effects of propagation. Many (37%) of the dE/dt signatures contain multiple peaks in the interval from 1 m s before to 1 m s after (-1 m s to +1 m s) the largest (dominant) peak, and 28% contain one or more peaks in the interval from 4 m s before to 1 m s before the dominant peak (-4 m s to -1 m s) and no additional peaks in the interval from -1 m s to +1 m s. When the integral of dE/dt is computed and compared with E, the integrated waveform, Eint, often has considerable fine-structure that is not resolved by the 10 MHz digitizer. This structure includes fast pulses near the beginning of the slow front, large peaks and shoulders within the slow front and during the fast transition, and very narrow peaks in Eint. Our overall conclusion is that the electromagnetic environment near the point(s) where lightning leaders attach to ground, and perhaps even the physics of the attachment process, is more complicated than is commonly assumed in the lightning literature.

 

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Initial Results from a Compact, High Time Resolution, Lightning Mapping
 

System William Rison, William P. Winn and Stephen J. Hunyady
Langmuir Laboratory New Mexico Institute of Mining and Technology Socorro, New Mexico 87801

 

During the summer of 2002 we deployed a compact lighting mapping system around Langmuir Laboratory in central New Mexico. In previous field programs the New Mexico Tech Lightning Mapping Array (LMA) has been deployed as an array of about twelve time-of-arrival (TOA) stations over an area with a diameter of about 60 km. In its compact form we put eight TOA stations over a 3 km area around Langmuir laboratory, with an addition four TOA stations over a surrounding 30 km area. The compact deployment has two advantages for lightning over the center of the array:

1) The system can locate impulsive events with with powers lower than can be located with a more spread out array. The minimum detectable power of the LMA in its normal deployment is about 1~W. For the compact deployment the LMA can detect events over the array with powers down to about 0.1~W.

2) The time resolution of a normally-deployed LMA is 100 µs --- i.e., each station detects the time of the highest peak in each 100 µs interval. In the compact deployment we reduce the time resolution to 10 µs.

With the higher time resolution and higher sensitivity the LMA produces much more detailed images of fast processes such as stepped leaders, dart leaders and K changes. For example, in a cloud-to-ground discharge we follow a branching stepped leader all the way to its ground strike point, and can resolve five distinct branches. In an intracloud discharge we locate about 100 sources in a K change with a duration of 7 ms. (When the data for this K-change is decimated to 100 µs windows, only 20 sources are located.)

 

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Tall structure lightning induced by sprite-producing discharges
 

Mark A. Stanley and Matthew J. Heavner
Space and Atmospheric Sciences, NIS-1, MS D466 Los Alamos National Laboratory Los Alamos, NM 87545 (505) 667-8353

 

It is well known that sprite-producing lightning discharges lower unusually large amounts of charge to earth. Experimental data suggests that the amount of charge removal is sufficiently large for the electric field below the base of the ionosphere (the upper electrode) to reach the conventional breakdown threshold. It will be shown in this paper that sprite-producing discharges will occassionally also induce breakdown from the other electrode; the ground.

On June 21, 1997, several sprites were documented on video over a small mesoscale convective system (MCS) near the Kennedy Space Center (KSC), Florida. All of the sprites were associated with horizontally-extensive positive cloud-to-ground (+CG) discharges. National Lightning Detection Network (NLDN) data indicated that a couple of the sprite-producing discharges also spawned one or more -CGs immediately following the +CGs. Curiously, these -CGs appeared to strike in the same location away from the convective cores where all the other -CGs were occurring. A comparison of the strike locations with those of tall structures revealed that a 460 meter tall tower was at the same location as the strikes. It will be shown that several of the sprite-producing discharges likely produced an electric field at the top of the tower which exceeded the breakdown strength of air, resulting in an upward positive leader.

Much like triggered lightning from wire-trailing rockets, the initial continuing current phases of upward positive leaders launched from towers can be, but are not necessarily, followed by relatively normal negative-polarity subsequent return strokes which can be detected and located with VLF sensors. The Los Alamos Sferic Array in Florida provides an ideal means by which potentially sprite-producing +CGs can be detected and the subsequent negative-polarity return stroke locations will be compared with those of tall structures.

 

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Design of Lightning Flash Observation and Ranging System
 

Tomoyuki Suzuki, Takatsugu Shimura and Koichiro Michimoto
(Japan Defense Agency)

 

We have operated summer thunderstorm observation project by X-band Doppler radar and LPATS since 1997 in Kanto plain, Japan. We expressed characteristics of generation and evolution of summer thunderstorms by Doppler radar, 2-D distribution of Cloud to ground (CG) flash by LPATS and relation between radar reflectivity and CG flash near the mountain area in Kanto plain on the 11th ICAE. We can observe a lot of interesting thunderstorms and analyze the detail of them (3-D). For example some of them were with rotation. But we couldn't get the details of lightning flash by LPATS because the only data that we can get is 2-D CG flash point and there is no 3-D lightning mapping system in Kanto plain. Thus, we designed the lightning flash data acquisition system and 3-D mapping system in order to investigate the detail of lightning flash event.

Followings are outline of our system.

(1) Long time data acquisition: (sampling rate 1M - 10M, acquisition time 1-2 s)

(2) Broadband: ELF - MF (300Hz-500KHz) and HF-UHF (20MHz - 500MHz)

(3) Maximum range: ELF-MF band is 400 `500km and HF-UHF band is 100`200km

We will observe the waveform of ELF-MF and the RF power of HF-UHF.

Presently, ELF-MF system was nearly finished and an experimental system has operated since this summer. HF-UHF system is under development. We hope to get many useful comments for our new observing system.

 

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The LMA Flash Algorithm
 

Ron Thomas, Paul Krehbiel, William Rison, Jeremiah Hamlin, Tim Harlin, Nathan Campbell
New Mexico Institute of Mining and Technology
Socorro, New Mexico, USA 87801

Ron Thomas, Professor and Chair of Electrical Engineering
(505)-835-5683
fax (505)-835-5332
http://www.ee.nmt.edu/~thomas/

 

We have developed a set of algorithms to divide and group data from the Lightning Mapping Array, LMA into flashes and classify them. Typical flashes observed by the LMA have hundreds to thousands of located RF sources. It is usually easy for a human to group the sources into flashes especially if the time development is recreated in an animation. We have used this manual flash grouping as our standard to test the algorithms. We assume that all the LMA sources that are in a group in both space and time belong to the same lightning flash. We require that the largest gap in the group be less than N Km and M ms (3 km and 150 ms work well). These parameters need to be adjusted depending on the array sensitivity, resolution and other factors. If they are too big separate flashes are joined together and if too small large flashes are broken into pieces. Spatially we normally use only the plan position and not altitude. We have also addressed the problem of decreasing resolution with distance from the array.

When the flash rates are not too large (less than about 20 flashes per minute) flashes are easily separated, but there are many "single point flashes" with 1 or a few points. Most of these are noise or poorly-located events that are labeled as noise or are joined to the proper flash. We have attempted to identify the true isolated discharge events that are important to understanding the storm and lightning processes.

When the flash rate is very large the noise and poorly located points can seem to link separate flashes together. We have added algorithms to correctly separate some of these.

After the sources have been grouped into flashes, the algorithms identify a number of parameters associated with each flash such as the number of points, area, duration, and initial velocity. These parameters along with associated NLDN locations are then used to classify the flashes (e.g. negative-CG, normal IC, low flash). At this point the flashes can be viewed and interactively reclassified if necessary.

 

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IMPACT-SAFIR Comparisons in Finland
 

Tapio J. Tuomi
Finnish Meteorological Institute P.O. Box 503 FIN-00101 Helsinki Finland

 

Finland has been covered by a five-sensor Impact/LP2000 ground lightning location system since 1997. In 2002, several Norwegian and Swedish sensors were also connected to improve the efficiency and accuracy. In 2001, a three-sensor Safir cloud/ground lightning location system was installed to cover a limited area in SW Finland. Due to incomplete sensor alignment and noisiness in one of the sites, the Safir locations are inaccurate. However, the accurate timing, about 0.1 millisecond, allows comparison of the two systems in the Safir detection area. In particular, Safir locates its observations at the VHF frequency range, and interprets some of the locations as ground strokes on the basis of the output from an LF antenna. Impact attempts to restrict its observations to ground strokes only. It turns out that the ratio of the numbers of ground strokes of Safir/Impact is 1.6 and the ratio of flashes is 1.5. It is suspected that discharge processes in the cloud contain LF components which may be misinterpreted as ground strokes. A case study from one day looks more closely at these differences. Another study considers cases where Impact detects weak positive strokes (below 5 kA), which in some situations can be very abundant. A general view is that they are mostly cloud lightning. In one third of the cases, Safir does interpret them as cloud lightning (not associated temporally with ground lightning); in one third, it identifies them with positive or negative ground strokes; and in one third, it identifies them as cloud processes associated with ground strokes (prestroke, interstroke or poststroke activity). Two more features are worth mentioning: Safir has a tendency to report very short interstroke intervals (below 10 ms); and the two systems often give opposing stroke polarities, sometimes associated with a small but significant time difference.

 

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Observations of radiations from airplane during STEPS
 

Yijun Zhang
Cold and Arid Regions Environmental & Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, P. R. China

P. Krehbiel, T. Hamlin, J. Harlin, R. Thomas, and W. Rison,
New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA

 

The electrical noise from airplane flying in clouds has been analyzed based on the data measured by three-dimensional lightning mapping array (LMA) system with high space and time resolution on the ground. The results indicated that the maximum powers vary from minimum locatable values of about 1W typically up to 10kW or more in the 60-66MHz passband of the receivers and the source powers of the radiations follow an approximate P-1distribution. This is a kind of electromagnetic radiation produced by point discharges on the airplane. The strongest radiations occurred when airplane flew at 10-12km altitude. The powers of radiation are different for different kind of cloud in which airplane flew through. The radiation sources were strongest when airplane flew through clouds in which lightning flashes were occurring in convection region and weakest in stratus.

 

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