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International Symposium on Lightning Protection, Kathmandu, Nepal, October 12-14, 2011
Fundamentals of Lightning
Vladimir A. RakovUniversity of Florida, Gainesville FL, USA
1
Outline
1. Introduction
2. Types of Lightning Discharges and Lightning Terminology
3. Downward Negative Lightning Discharges to Ground
4. Upward Lightning Initiated by Ground-Based Objects
Fundamentals of Lightning
4. Upward Lightning Initiated by Ground-Based Objects
5. Positive and Bipolar Lightning Discharges to Ground
6. Rocket-Triggered Lightning
7. Summary
2
Lightning Incidence – Global
A global map of total lightning flash density (per square kilometer per
year) based on data from two satellite detectors, Optical Transient
Detector (5 years) and Lightning Imaging Sensor (3 years)
3
2. Types of Lightning Discharges
4
Cloud-to-
Cloud discharges (75%)
2. Types of Lightning Discharges
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25%) Cloud-to-air
Intracloud
Cloud-to-
cloud
5
5
Types of Cloud-to-Ground Lightning Discharges
6
Four types of lightning effectively lowering cloud charge to ground. Only the initial leader is
shown for each type. In each lightning-type name given below the sketch, the direction of
propagation of the leader and the polarity of the cloud charge effectively lowered to
ground are indicated.
3. Downward Negative Lightning
Discharges to Ground
7
3. Downward Negative Lightning Discharges to Ground
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current
at the channel base: (a) still-camera image, (b) streak-camera image, and (c) channel-base
current.
8
Histograms of number of
strokes per flash from
correlated electric-field
and optical records: (a)
76 flashes in Florida
(Rakov and Uman 1990a)
and (b) 83 flashes in New
Mexico (Kitagawa et al.
Number of Strokes per Flash – Florida and New Mexico
(a)
9
Mexico (Kitagawa et al.
1962). The percentage of
single-stroke flashes is
17% in (a) and 13% in
(b). Adapted from Rakov
and Uman (1990d).
(b)
Number of Strokes per Flash
Location
(Reference)
Average Number
of Strokes per
Flash
Percentage of
Single-Stroke
Flashes
Sample Size
New Mexico
(Kitagawa et al., 1962) 6.4 13% 83
Florida
(Rakov and Uman, 1990a) 4.6 17% 76
Sweden
10
Sweden
(Cooray and Perez, 1994) 3.4 18% 137
Sri Lanka
(Cooray and Jayaratne, 1994) 4.5 21% 81
Brazil
(Saraiva et al., 2010) 3.9 20% 223
Arizona
(Saraiva et al., 2010) 3.9 19% 209
Multiple Channel Terminations on Ground
11
Number of Channel Terminations per Flash
Location
(Reference)
Average Number
of Channels per
Flash
Percentage of
Multigrounded
Flashes
Sample
Size
New Mexico
(Kitagawa et al., 1962)
1.7
1.6
49%
42%
72*
83**
Florida
(Rakov and Uman, 1990) 1.7 50% 76
Arizona
(Valine and Krider, 2002) 1.4 35% 386
12
(Valine and Krider, 2002) 1.4 35% 386
France
(Berger et al., 1996; Hermant, 2000) 1.5 34% 2995
Brazil
(Saraiva et al., 2010) 1.7 51% 138
Arizona
(Saraiva et al., 2010) 1.7 48% 206
* multiple-stroke flashes only
** including 11 single-stroke flashes assumed to have single channel per flash
Multiple Channel Terminations on Ground
Min = 0.3 km
Max = 7.3 km
GM = 1.7 km
13
Histogram of the distances between the multiple terminations of 22 individual ground
flashes in Florida. The distances were determined using optical triangulation and
thunder ranging. Adapted from Thottappillil et al. (1992).
GM = 1.7 km
4. Upward Lightning Initiated by Ground-
Based Objects
14
Based Objects
Lightning Initiated by Ground-Based Objects
15
Diagram showing the luminosity of an upward negative flash and the corresponding current at
the channel base: (a) Still-camera image, (b) streak-camera image, and (c) channel-base
current.
UPL = Upward Positive Leader; ICC = Initial Continuous Current; UPL + ICC = Initial Stage (IS) Current; DL = Dart Leader; RS = Return Stroke
25 to 50 %
contain return
strokes
03.8.2001 06:58:24
100 ms
Imax = 20 kA
Q tot = 129 As
14 Pulses
Courtesy of Dr. G. Diendorfer
16
Upward lightning initiated from the
Upward Lightning Initiated by Ground-Based Objects
17
initiated from the
818 m tall Dubai Tower.
Upward Lightning Initiated by Ground-Based Objects
818 mOstankino TV Tower, Moscow, Russia 540 m
Guangzhou New TV Tower, China 610 m
Tokyo Sky Tree (to open in 2012), Japan 634 m
18
Canary Wharf
(London)
Empire State
(New York)
Petronas Towers
(Kuala Lumpur)
Sears Tower
(Chicago)
Taipei 101
(Taipei)
CN Tower
(Toronto)
KVLY-TV Mast
(North Dakota)
Dubai Tower (Dubai)
5. Positive and Bipolar Lightning
Discharges to Ground
19
Positive lightning discharges have recently attracted
considerable attention for the following reasons:
• The highest recorded lightning currents (near 300 kA) and the largest charge transfers to ground (hundreds of coulombs or even more) are thought to be associated with positive lightning.
5. Positive and Bipolar Lightning Discharges to Ground
20
to be associated with positive lightning.
• Positive lightning can be dominant type of cloud-to- ground lightning during the cold season, during the dissipating stage of a thunderstorm, and in some other situations.
5. Positive and Bipolar Lightning Discharges to Ground
Directly measured currents in three positive lightning discharges in Japan. The insets in the
middle and bottom diagrams show the current on an expanded scale. The transferred
charges, from top to bottom, are 330,180, and 400 C. Adapted from Goto and Narita (1995).
21
Lightning Damage to an Optical Fiber Ground Wire (OPGW)
Courtesy of Prof. Dr. Silverio Visacro Filho
22
Although the overall percentage of positive lightning discharges isrelatively low, there are five situations, listed below that appear to be conducive to the more frequent occurrence of such discharges.
1. The dissipating stage of an individual thunderstorm
2. Winter thunderstorms
Conditions conducive to the occurrence of positive lightning
3. Shallow clouds such as the trailing stratiform regions of mesoscale convective systems (MCSs)
4. Severe storms
5. Thunderclouds formed over forest fires or contaminated by smoke
23
Figure 5.2Figure 5.2
The percentage of positive flashes over the contiguous United States as a function of month
for each of the years 1995 through 1997. The minimum occurs in late summer and the
maximum is in January-February. Adapted from Orville and Huffines (1999).
24
Observed polarity of currents in winter lightning in Japan (6 to 14% in summer)
Bipolar Flashes - Statistics
Source Strike Object Observation
Period
Number
of Positive
(percent)
Number
of
Negative
(percent)
Number
of Bipolar
(percent)
Total
(percent)
Miyake et
al. (1992)
88-m weather
observation tower at
Kashiwazaki and 200-m
stack at Fukui
1978-1986 41
(33)
78
(62)
6a
(5)
125
(100)
Goto and
Narita
150-m meteorological
tower at Maki
1982-1993 25
(17)
91
(63)
29
(20)
145
(100)
a Five changes from negative to positive and one change from positive to negative.b Changes from negative to positive (Wada et al. , 1996a).
Narita
(1995)
tower at Maki (17) (63) (20) (100)
Wada et al.
(1996a, b)
200-m stack at Fukui 1989-1994 4
(9)
36
(80)
5b
(11)
45
(100)
Nagai et al.
(1996)
500-kV Genden-Tsuruga
transmission line tower
1986-1992 1
(4)
15
(63)
8
(33)
24
(100)
Wang et al.
(2010,
ICLP)
100-m windmill and its
105-m protection tower
at Uchinada
2005-2009 8
(15)
36
(70)
8
(15)
52
(100)
Bipolar Flashes – Types 1 and 2
Sketches of overall-flash current records to illustrate different types of bipolar lightning
discharges. RS=Return Stroke.
26
Bipolar Flashes – Types 3a and 3b
Sketches of overall-flash current records to illustrate different types of bipolar lightning
discharges (cont’d).
27
Bipolar Flash – Type 2
28
(a) Concurrent upward bipolar flash (on the right) and upward negative flash (on the left) from
towers 1 and 2, respectively, on Monte San Salvatore (event 6439). (b) The currents
measured at tower 1 (top trace) and at tower 2 (bottom trace). The time scale (which is in
seconds) on the bottom trace also applies to the top trace. Adapted from Berger and
Vogelsanger (1966).
Bipolar Flash - Type 3a (Upward Flash)
29
Portion of four-stroke bipolar flash #312 initiated from the 100-m Gaisberg tower,
Austria. Adapted from Schulz and Diendorfer (2003).
6. Rocket-Triggered Lightning
30
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
6. Rocket-Triggered Lightning
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
31
31
Leader/Return Stroke SequenceInitial Stage
6. Rocket-Triggered Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov, 1999]
32
Rocket-triggered lightning vs. natural lightning
Natural
~ 5 C ~ 1 C ~ 10 C ~ 1 C
Triggered
Initial Stage
(50 – 500 A)
~ 30 C ~ 10 C ~ 1 C ~ 1 C
33
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)Melbourne, Florida in 1983) 1991 (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
34
The International Center for Lightning Research and Testing (ICLRT) at
Camp Blanding, Florida
Overview of the ICLRT, 2000 - 2007
35
1993 - 2011 Triggered-Lightning Experiments at the ICLRT at Camp Blanding, Florida
Year(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. 52001 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 - Sept. 27
2011 1 16 12 1 Jan. 25 - present
1993-2011
(18* years)
383 273
(71%)
7
(1.8%)
* There was no lightning triggering
in 2006
The International Center for Lightning Research and Testing (ICLRT) at
Camp Blanding, Florida (http://www.lightning.ece.ufl.edu)
Australia: M. Darveniza
Austria: G. Diendorfer,
M. Mair
Canada: H. Mercure,
S. Cyr
France: A. Eybert-Berard,
J. P. Berlandis,
B. Bador,
P. Lalande,
P. Laroche,
Japan: D. Wang,
M. Miki,
S. Yoshida
Norway: H. Hoidalen
Poland: K. Chrzan,
G. Maslowski
Russia: V. Lebedev
Sri Lanka: P. Liyanage
37
P. Laroche,
S. Chauzy,
S. Soula
Germany: J. Kallweit,
J. Schoene
Iran: R. Moini
Italy: C. A. Nucci,
S. Guerrieri,
M. Paolone
Sweden: V. Cooray,
M. Rahman
Switzerland: F. Rachidi,
M. Rubinstein,
E. Petrache
USA: R. Fisher,
(partial) G. Schnetzer,
C. Weidman,
V. Idone,
W. Beasley,
H. Christian,
E.P. Krider
ICLRT
1-mRocket
38
Fiberglass rocket with a spool of Kevlar-coated copper wire.
Wire spool
Photographs of lightning
flashes triggered in 1997 at
the ICLRT at Camp
Blanding, Florida. Top, a
distant view of a strike to
the test runway; bottom, a
ICLRT
39
close-up view of a strike to
the test power system
initiated from the 11-m
high tower launcher.
ICLRT
40
A lightning strike initiated in 1999 from the underground launcher at the center of a 70 × 70 m2 buried metallic grid
ICLRT
A lightning strike initiated in 2003 from the mobile launcher
41
ICLRT
42
Still picture of a multiple-stroke flash triggered at Camp Blanding, Florida.
This flash started a grass fire.43
ICLRT
Anomalous Triggered Lightning Flash
44
ICLRT
Lightning channel branch terminating on the lightning protective
system of the Launch Control Trailer.
45
“Faraday cage” effect
Lightning strike to a car with a live rabbit inside. Courtesy of S. Sumi.
46
0401_LC_Tower_Normal
47
0401_LC_Tower_Slow
48
F0312-LC-NORMAL
49
F0321-OFFICE-WIDE
50
7. Summary
51
Summary
• About 80% or more of cloud-to-ground lightning flashes are composed of two or more strokes. This percentage is appreciably higher than 55% previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5.
• Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers. When only one location per flash is recorded, the correction factor for only one location per flash is recorded, the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 1.5-1.7, which is considerably higher than 1.1 estimated by Anderson and Eriksson (1980).
• In upward (object-initiated) and rocket-triggered flashes, the first stroke, in effect, is replaced by the initial-stage current, while subsequent strokes are similar to those in downward flashes.
Summary (continued)
• Although positive lightning discharges account for 10% or less of global cloud-to-ground lightning activity, there are several situations, including winter storms, that appear to be conducive to the more frequent occurrence of positive lightning.
• The highest directly measured lightning currents (near 300 kA) and the largest charge transfers (hundreds of coulombs or more) are thought to be associated with positive lightning. to be associated with positive lightning.
• Bipolar lightning is a poorly understood and often unrecognized phenomenon. Bipolar discharges are usually initiated by upward leaders from tall objects. However, natural downward flashes also can be bipolar.
Monte San Salvatore Tower (70 m), Lugano, Switzerland
54
Courtesy of Prof. R.E. Orville, Texas A&M
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
The International Center for Lightning Research and Testing (ICLRT) at
Camp Blanding, Florida (http://www.lightning.ece.ufl.edu)
55
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).
Effects of lightning on underground power cables
Barker (1993)
C
B
A
56
Effects of lightning on underground power cables
Lightning damage to underground power cables
57
Effects of lightning on underground power cables
Lightning damage to underground power cables
58
World’s longest excavated fulgurite (about 5 m), made by triggered lightning at
Camp Blanding in 1996
59
Dart leaderStepped leader
Characterization of negative cloud-to-ground lightning
Dart-stepped leader
10. Summary of Salient Lightning Properties
Dart-stepped leader
Subsequent return strokeьFirst return strokeь
60
Continuing current (longer than
~40 ms)c
Overall flash
Characterization of negative cloud-to-ground lightning
10. Summary of Salient Lightning Properties
M-component ь
61