vladimir a. rakov university of florida, gainesville fl, usa · vladimir a. rakov university of...

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