A Review of Triggered-Lightning Experiments
University of Florida, Gainesville, Florida, USA
30th International Conference on Lightning ProtectionCagliari, Italy, September 13-17, 2010
Vladimir A. RakovDepartment of Electrical and Computer Engineering
Outline
1. Artificial Initiation (Triggering) of Lightning from Natural Thunderclouds
2. Overview of Triggered-Lightning Programs
3. The International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida
4. Close Lightning Electromagnetic Environment
5. Return-Stroke Current Peaks and Risetimes
6. Continuing Currents and M-Components
7. Evaluation of the Performance Characteristics of the US National Lightning Detection Network (NLDN)
8. Lightning Attachment Process
9. Interaction of Lightning with Man-Made Systems
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A Review of Triggered-Lightning Experiments
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a “classical” rocket.
The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kV/m, and near the tip of the rocket, where they are concentrated geometrically. They are further apart near the ground, where the field is greatly reduced by corona space charge.
Instrumentedtriggering facility
wire
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1. Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov, 1999]
Leader/Return Stroke SequenceInitial Stage
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1. Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs. natural lightning (current as a function of time)
Natural
Triggered
Initial Stage (50 – 500 A)
~ 5 C ~ 1 C ~ 10 C ~ 1 C
~ 30 C ~ 10 C ~ 1 C ~ 1 C
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I
I
t
t
1. Artificial Initiation (Triggering) of Lightning
Altitude Triggering
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Overview of major triggered-lightning programs (also experiments in Germany, Indonesia, and Russia)
Experimental site Height abovesea
level, m
Years of operation
Wire material
Location of
wire spool
Selectedreferences
Saint Privat d’Allier, France 1100 1973-1996
Steel or copper
Ground or rocket
Fieux et al. (1978), SPARG (1982)
Kahokugata, Hokuriku coast, Japan
0 1977-1985
Steel Ground Horii (1982), Kito et al. (1985)
Langmuir Laboratory, New Mexico
3230 1979-present
Steel Ground Hubert et al. (1984), Idone et al. (1984)
KSC, Florida (south of Melbourne, Florida in 1983)
0 1983-1991
Copper Rocket Eybert-Berard et al. (1986,1988),Willett(1992)
Okushishiku, Japan 930 1986-1998
Steel Ground or rocket
Nakamura et al. (1991, 1992)
Different sites in China Various 1989-present
Steel or copper
Ground or rocket
Liu et al. (1994),Qie et al. (2007)
Fort McClellan, Alabama 190 1991-1995
Copper Rocket Fisher et al. (1993), Morris et al. (1994)
20-25 1993-present
Copper Rocket Uman et al. (1997),
570 1999-2007 Copper Rocket Saba et al. (2000, 2003),Solorzano et al. (2002)
Rakov et al. (1998, 2004)Camp Blanding, Florida
Cachoeira Paulista, Brazil
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Currents in New Mexico triggered-lightning: (A) classical, (B) slow, (C) anomalous, and (D) pseudo-classical. The vertical bars above the curves indicate the time and the peak intensity of the main current pulses. Adapted from Hubert et al. (1984).
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New Mexico, 1981
The overall current record, including the initial continuous current (ICC), of a flash triggered at Fort McClellan, Alabama, in 1991. Return strokes are numbered 1 through 9. The recording saturation level occurs at 2 kA. Adapted from Fisher et al. (1993).
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Alabama, 1991
Current record of a flash triggered at the Kennedy Space Center (KSC), Florida, in 1990. (a) Overall current record excluding the ICC with upper saturation level at about 1 kA and a noise floor of about 4 A. The return strokes are numbered 1 through 10. Examples of interstroke interval (II), total stroke duration (TSD), and no-current interstroke interval (NII) are marked. (b) Same as (a), but with upper saturation level of about 75 A and a noise floor less than 2 A. Adapted from Fisher et al. (1993).
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Florida, 1990
Triggered-Lightning Experiments in Japan
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K. Horii, K. Nakamura, and S. Sumi, Review of the experiment of triggered lightning by rocket in Japan, ICLP 2006, Kanazawa, Japan
“Faraday cage” effect
Lightning strike to a car with a live rabbit inside. Courtesy of S. Sumi.
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Lightning Triggering Sites in China
The first successful rocket-and-wire lightning triggering in China was conducted in 1977 by the Chinese Academy of Sciences (CAS).More than 80 flashes were triggered in 7 different areas since then.Two sites are presently operated by CAS and CMA (Chinese Meterological Administration).
Conghua,1998-2000
Binzou2005-, CAS
Triggering Sites
Shanghai1995
Nanchang,1993-94
Beijing,1992-93Gansu1977,1989-92; 2001
Tibet, 2004
Binzhou2005-, CAS
Conghua,2006-, CMA
Courtesy: Dr. Xiushu Qie, Chinese Academy of Sciences
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Photograph of a lightningflash triggered in CachoeraPaulista, Brazil on November23, 2000. Courtesy Dr. OsmarPinto Junior, INPE.
Altitude-triggered lightning, Brazil
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ICLRT at Camp Blanding, Florida 2009
Overview of the ICLRT
The International Center for Lightning Research and Testing (ICLRT) atCamp Blanding, Florida
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The lightning-triggering facility at Camp Blanding, Florida, was established in 1993 by the Electric Power Research Institute (EPRI) and Power Technologies, Inc. (PTI). Since September 1994, the facility has been operated by the University of Florida (UF). Over 40 researchers (excluding UF faculty, students, and staff) from 15 countries representing 4 continents have performed experiments at Camp Blanding concerned with various aspects of atmospheric electricity, lightning, and lightning protection. Since 1995, the Camp Blanding facility has been referred to as the International Center for Lightning Research and Testing (ICLRT). Presently it is jointly operated by UF and Florida Institute of Technology (FIT) and additionally includes the Lightning Observatory in Gainesville (LOG).
The International Center for Lightning Research and Testing (ICLRT) atCamp Blanding, Florida (http://www.lightning.ece.ufl.edu)
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The International Center for Lightning Research and Testing (ICLRT) atCamp Blanding, Florida (http://www.lightning.ece.ufl.edu)
Australia: M. Darveniza
Austria: G. Diendorfer,M. Mair
Canada: H. MercureS. Cyr
France: A. Eybert-Berard,J. P. Berlandis,B. Bador,P. Lalande,P. Laroche, S. Chauzy,S. SoulaA. Rousseau
Germany: J. Kallweit,J. Schoene
Iran: R. Moini
Italy: C. A. Nucci,S. Guerrieri,M. Paolone
Japan: D. Wang,M. Miki,S. Yoshida
Norway: H. Hoildalen
Poland: K. Chrzan,G. Maslowski
Russia: V. Lebedev
Sri Lanka: P. Liyanage
Sweden: V. Cooray,M. Rahman
Switzerland: F. Rachidi,M. Rubinstein,E. Petrache
USA: R. Fisher,(partial) G. Schnetzer,
C. Weidman,V. IdoneM. Guthrie
1993 - 2010 Triggered-Lightning Experiments at the ICLRT at Camp Blanding, FloridaYear(s) Rocket
Launchers Used
Total Flashes Triggered
Flashes With Return Strokes
Positive orBipolarFlashes
Time Period
1993 1 32 22 - June 7 – Sept. 21
1994 2 15 11 - August 4 – Sept.
1995 2 14 13 - June 25 – August 19
1996 2 30 25 - June 20 – Sept. 11
1997 4 48 28 1 May 24 - Sept. 26
1998 3 34 27 - May 15, July 24 – Sept. 30
1999 2 30 22 1 Jan 23, June 26 – Sept. 27
2000 2 30 27 - June 12 – Sept. 6
2001 2 23 11 - July 13 – Sept. 5
2002 2 19 14 - July 9 – Sept. 13
2003 2 24 12 1 June 30 – Aug. 15
2004 1 5 3 - June 23 – July 24
2005 2 11 8 - July 2 – August 5
2007 1 2 1 - July 13 – July 31
2008 1 11 7 1 May 16 – Oct. 9
2009 1 26 18 2 Febr. 19 – August 18
2010 2 13 12 - June 5 - present
1993-2010(17* years)
367 261(71%)
6(1.6%)
* There was no lightning triggering in 2006
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Fiberglass rocket with a spool of Kevlar-coated copper wire.
ICLRT
Wire spool
1-mRocket
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Photographs of lightningflashes triggered in 1997 atthe ICLRT at CampBlanding, Florida. Top, adistant view of a strike tothe test runway; bottom, aclose-up view of a strike tothe test power systeminitiated from the 11-mhigh tower launcher.
ICLRT
Camp Blanding, June 5, 2010, 3 strokes
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Camp Blanding, June 17, 2010, 8 strokes
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Close Lightning Electromagnetic Environment
Electric field and electric field derivative (dE/dt) waveforms for stroke 2 in rocket-triggered flash S9918 measured at 15 and 30 m from the lightning channel at Camp Blanding, Florida.
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Close Lightning Electric Fields: Variation with Distance
Electric field waveforms of the first leader/return-stroke sequence of flash S9721 as recorded in 1997 at distances (a) 10, 20, and 30 m and (b) 50, 110, and 500 m at Camp Blanding, Florida. The initial downward-going portion of the waveform is due to the dart leader, and the upward-going portion is due to the return stroke. Adapted from Crawford et al. (1999).
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Return-stroke current peak
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes, Camp Blanding, Florida, 1999 – 2004, power line experiments. An adjustment factor of 0.75 has been applied to the current peaks from the 2000 experiment. Adapted from Schoene et al. (2009).
Direct strikes (n = 144) : GM = 12 kA
Nearby strikes (n = 21): GM = 11 kA
Total (n = 165): GM = 12 kA
Direct strikes are to an overheadpower line conductor (initial inputimpedance of about 200 Ω).
Nearby strikes are to a 8-m longvertical conductor connected to aconcentrated grounding system.
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Direct and nearby strikes (n = 81)GM = 0.9 µsAM = 1.2 µs
Direct strikes (n=63)GM = 1.2 µsAM = 1.4 µs
Nearby strikes (n = 18)GM = 0.4 µsAM = 0.5 µs
Histograms of return stroke current 10-90%risetimes for 81 return strokes in rocket-triggeredflashes, Camp Blanding, Florida, 1999-2004,power-line experiments. a) Direct and nearbystrikes, b) only direct strikes, and c) only nearbystrikes. The horizontal scale in a) and b) isinterrupted between 2.8 and 5.6 μs. The verticaland horizontal scales in c) are different from thescales in a) and b). Adapted from Schoene et al.(2009).
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Current risetime
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Examples of continuing-current waveshapes in triggered lightning. In each figure, the arrow indicates the assumed beginning of the continuing current. The number in the upper left corner indicates the order of the return stroke in the flash. (a) Type I, more or less exponential decay with superimposed M-current pulses; (b) type II, a hump with superimposed M-current pulses followed by relatively smooth decay; (c) type III, a slow increase and decrease in current, with superimposed M-current pulses throughout; (d) type IV, a hump with superimposed M-current pulses followed by a steady plateau without pronounced pulse activity. Adapted from Fisher et al. (1993).
Continuing Currents and M-Components
Examples of typical current pulses. (a) A typical return stroke pulse with a fast wave front and slower tail. (b) A typical M-component pulse with a more or less symmetrical wave shape. Note the more than 3 orders of magnitude difference in rise time. Adapted from Fisher et al. (1993).
Portion of current record showing return stroke and two M-component pulses with a 1 kA saturation level. Adapted from Fisher et al. (1993).
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Return Strokes vs. M-components
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Three Modes of Charge Transfer to Ground
Current profiles for threemodes of chargetransfer to ground insubsequent lightningstrokes:
(a) dart leader/return stroke sequence,
(b) continuing current, and
(c) M-component.
Map showing the locations of NLDN sensors in the Florida region. Also shown is the location of lightning triggering site, labeled “Camp Blanding”. The nearest NLDN sensor is located in Ocala, at a distance of 89 km. Adapted from Jerauld et al. (2005).
Evaluation of performance characteristics of the NLDN
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Flash and Stroke Detection Efficiencies
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Location Accuracy
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Histogram of the NLDN absolute location errors. Corresponding statistics are given for both 2004-2009 (present study) and 2001-2003 [Jerauld et al. 2005].
Peak Current Estimates
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NLDN-reported peak current versus peak current directly measured at Camp Blanding for (a) 2004-2009 (present study) and (b) 2001-2003 [Jerauld et al. 2005].
Absolute current estimation errors range from 0 to 129% (Median = 13%, n = 96)
Absolute current estimation errors range from 0 to 50% (Median = 20%, n = 70)
Adapted from Howard (2009)39
Lightning Attachment Process
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Optical Images of Leader and Attachment Process – Triggered Lightning
Dart-stepped leader and attachement process in rocket-triggered lightning (Sept. 17, 2008) at Camp Blanding, Florida; Photron FASTCAM SA1.1, 50000 fps (20 µs per frame)
Biagi et al. (2009, GRL)2 frames before return stroke 8 1 frame before return stroke 8
56 m
16 m
25 m
The International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida, 2005
N
2004-2005 Test House experiments
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The primary objective was to examine current division between local (at the Test House) and remote (at IS1) grounding systems.
The test house at the ICLRT whose LPS was subjected to direct lightning strikes in 2004 and 2005. Approximate dimensions of the house are 10 x 7 x 6.5 m3. Photo from 2005.
2004-2005 Test House experiments
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(a) Injected current versus the difference between the sum of the four downlead currents and current D, labeled (Sum – D). The (Sum – D) waveform is scaled so that its peak is equal to that of the injected current and represents the current going to the grounding system (local) of the test house. (b) Current D versus current G.
Current division results (2005)
(a)
(b)
0 20 40 60 80 100-10
-5
0
Time, μs
Cur
rent
, kA
0521-1Injected Current(Sum - D), scaled
0 20 40 60 80 100-6
-4
-2
0
Time, μs
Cur
rent
, kA
0521-1Current DCurrent G
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(Sum-D) is the current dissipated by the grounding system of the Test House.
D is the current entering the electrical circuit neutral (59% of the injected current, on average).
G is the current dissipated by the remote ground.
Damage to the system (2005)
Damage to the insulation of the 600-V cable, (a) puncture of the insulation of one conductor of the 600-V cable, (b) damage to all three conductors of the cable.
y
4 mm Adjacent damage
(b)(a)
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Summary
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Triggered-lightning experiments have provided considerable insight into natural lightning processes. Among such findings are:
• Observation of an upward connecting leader in a dart leader/return stroke sequence• Identification of the M-component mode of charge transfer to ground• Observation of a lack of dependence of return stroke current peak on grounding conditions• Discovery of X-rays produced by dart and dart-stepped leaders• Direct measurements of NOx production by an isolated lightning channel section• Characterization of the electromagnetic environment within tens to hundreds of meters of the lightning channel
Triggered-lightning experiments have contributed significantly to testing the validity of various lightning models and to providing ground-truth data for the U.S. National Lightning Detection Network (NLDN).
Triggered lightning is a very useful tool to study the interaction of lightning with various objects and systems.
