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Principles of Lightning Physics

Principles of Lightning Physics

Vladislav MazurNational Severe Storms Laboratory, Norman, Oklahoma, USA

IOP Publishing, Bristol, UK

ª IOP Publishing Ltd 2016

All rights reserved. No part of this publication may be reproduced, stored in a retrieval systemor transmitted in any form or by any means, electronic, mechanical, photocopying, recordingor otherwise, without the prior permission of the publisher, or as expressly permitted by law orunder terms agreed with the appropriate rights organization. Multiple copying is permitted inaccordance with the terms of licences issued by the Copyright Licensing Agency, the CopyrightClearance Centre and other reproduction rights organisations.

Permission to make use of IOP Publishing content other than as set out above may be soughtat permissions@iop.org.

Vladislav Mazur has asserted his right to be identified as the author of this work in accordancewith sections 77 and 78 of the Copyright, Designs and Patents Act 1988.

Video content is available from the book information online: https://doi.org/10.1088/978-0-7503-1152-6.

ISBN 978-0-7503-1152-6 (ebook)ISBN 978-0-7503-1153-3 (print)ISBN 978-0-7503-1154-0 (mobi)

DOI 10.1088/978-0-7503-1152-6

Version: 20161201

IOP Expanding PhysicsISSN 2053-2563 (online)ISSN 2054-7315 (print)

British Library Cataloguing-in-Publication Data: A catalogue record for this book is availablefrom the British Library.

Published by IOP Publishing, wholly owned by The Institute of Physics, London

IOP Publishing, Temple Circus, Temple Way, Bristol, BS1 6HG, UK

US Office: IOP Publishing, Inc., 190 North Independence Mall West, Suite 601, Philadelphia,PA 19106, USA

Cover image: Summer lightning storm near Tucson, Arizona, USA. Credit: Keith Kent/SciencePhoto Library

To Marijo, my beloved wife,without whose encouragement and supportthis book would not have been possible

Contents

Preface xi

Acknowledgements xiv

Author biography xv

1 The components of lightning 1-1

1.1 Features of lightning plasma 1-1

1.2 Lightning is more than a spark 1-2

1.2.1 Corona glow 1-2

1.2.2 Corona streamers 1-3

1.2.3 Transition from corona streamers to a positive leader 1-5

1.2.4 Transition from corona streamers to a negative leader 1-6

1.3 Conditions for leader propagation 1-8

1.4 Lightning leaders in nature 1-12

References 1-15

2 Lightning leaders versus free-burning arcs 2-1

2.1 Similarities and differences 2-1

2.2 The E–I relationship, from the results of laboratory measurements andthe modeling of free-burning arcs

2-2

2.3 The E–I relationship and the luminosity of leader channels 2-7

References 2-9

3 Physical concepts of a lightning leader model 3-1

3.1 The space charge leader concept based on cloud charge collection 3-1

3.2 The bi-directional, uncharged leader concept based on induced charges 3-3

3.3 Comparing the outputs of the two leader models 3-5

References 3-8

4 Verifying the concept of the bidirectional leader 4-1

4.1 How studying lightning strikes to aircraft has helped to solvethe puzzle of lightning development

4-1

4.1.1 Lightning radar echo 4-2

4.2 How does an aircraft trigger lightning? 4-5

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4.3 Environmental conditions that lead to aircraft-triggered lightning 4-9

4.3.1 Hypothesis of a natural lightning-triggering mechanism inthunderstorms

4-11

References 4-13

5 Defining the types of lightning 5-1

5.1 The visible features of lightning flashes 5-1

5.2 Defining the types of lightning using the bidirectional, bipolarleader concept

5-7

5.2.1 Intra-cloud flashes 5-7

5.2.2 Cloud-to-ground flashes 5-11

References 5-14

6 The electrostatic theory of lightning discharges 6-1

6.1 Cloud potential and induced charges of lightning 6-1

6.2 The relationship between the electric fields produced by leadersand return strokes

6-2

6.3 The relationship between lightning processes and space charges inthunderstorms

6-4

6.3.1 Thunderstorm model 6-4

6.3.2 Development of the cloud-to-ground leader 6-6

6.3.3 Return stroke 6-11

6.3.4 Electric field changes produced by CG flashes 6-12

6.3.5 Development of the intra-cloud leader 6-13

6.4 Applications and limitations of the electrostatic model 6-14

References 6-17

7 Lightning triggered by rockets with wire and by tall structures 7-1

7.1 The idea of artificially triggered lightning 7-1

7.2 Concept and features of the classic rocket-triggered lightning technique 7-2

7.2.1 Processes related to melting of the trailing wire 7-3

7.3 Concept and features of the altitude-triggered lightning technique 7-6

7.4 Conditions required for triggering lightning with rocket-and-wiretechniques

7-7

7.5 On leaders and return strokes in rocket-triggered lightning 7-8

7.6 Upward lightning triggered by tall ground structures 7-9

7.6.1 Conditions for upward lightning initiation 7-9

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7.6.2 Understanding luminosity variations in the upward-lightningchannel

7-12

7.7 Features of positive and negative leaders determined from studies oftriggered lightning

7-15

References 7-18

8 Understanding current cutoff in lightning 8-1

8.1 Definition and manifestation of current cutoff in differentlightning events

8-1

8.2 The death of the leader in unbranched lightning channels 8-2

8.3 Current cutoff in branched leaders 8-3

8.3.1 The screening effect in single and branched channels 8-3

8.3.2 The role of branch-screening in current cutoff 8-4

8.4 Arc instability and current cutoff 8-8

References 8-9

9 The phenomenon of recoil leaders 9-1

9.1 The nature of recoil and dart leaders 9-1

9.2 The relationship between recoil leaders and M-events: causeand effect

9-5

9.3 The electrostatic model of an M-event that produces anM-component

9-9

9.3.1 The electrostatic model of a dart leader–return strokesequence in CG flashes

9-10

9.3.2 The electrostatic model of an M-event 9-12

9.4 The universal nature of M-events in lightning 9-14

References 9-15

10 The physical concept of recoil leader formation 10-1

10.1 The relationship between the internal electric field and current inlightning leaders

10-1

10.2 Current cutoff prior to the occurrence of recoil leaders 10-2

10.3 The development of recoil leaders 10-3

10.4 A proposed conceptual model of recoil leader formation 10-5

10.4.1 Recoil leader formation and polarity asymmetry inbranched leaders

10-8

10.5 Conclusion 10-10

References 10-10

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11 Some lightning protection issues viewed through the lens oflightning physics

11-1

11.1 Striking distance versus the parameters of downward leaders inlightning protection of ground installations

11-1

11.2 A physical model of leader interaction with a ground structure 11-4

11.3 On the hazardous effects of upward lightning to tall structures 11-8

11.4 Sharp-tipped versus blunt-tipped lightning rods 11-8

11.5 Lightning protection of aircraft 11-9

References 11-11

12 Lightning initiation—the most difficult issue oflightning physics

12-1

12.1 Hydrometeor theory of lightning initiation 12-1

12.2 The runaway theory of lightning initiation 12-4

12.3 Evidence supporting the hydrometeor theory of lightning initiation 12-5

References 12-8

Appendix A-1

Principles of Lightning Physics

x

Preface

Lightning, for the average person, remains a puzzling mystery and, to some degree,this is also true for the scientists who study it. For a long time, researchers observedand described some of the physical characteristics of lightning as they weremanifested in the behavior of its luminous channels and the changes in theelectromagnetic field that lightning produces. However, these efforts were able toextract from this information only a few pieces of the giant jigsaw puzzle that we callthe ‘lightning phenomenon’. The literature available on lightning has reflectedalmost exclusively this predominantly ‘descriptive’ approach to lightning studies,focusing either on individual, sometimes anomalous, lightning cases, or on compar-ing the various characteristics of lightning flashes that occur in different geographicregions.

The field of lightning research is a rather narrow one in comparison, for example,with that of meteorology. The lightning research community, similarly, is relativelysmall. The horizon of unexplored issues and unanswered questions, on the otherhand, is still very broad—as are the possibilities of making some major discoveries.In my adopted country, the United States of America, and in several other countries,the past 30 years have proven to be among the most exciting and productive ever inthe field of lightning studies. Aided by newly developed observational tools,significant progress has been made in our understanding of lightning’s essentialprocesses. I have been fortunate to be an active participant in, and contributor to,many of the major advances achieved during this period. The search for the physicalfeatures common to all kinds of lightning discharges has been the strongestmotivation in my long career as a lightning researcher. Most of my publishedpapers, as well as those written together with my long-term collaborator, Dr LotharH Ruhnke, have been devoted to uncovering the key physical processes that governthe different aspects of the lightning phenomenon.

Until now, there has been no book available in the literature on lightning thatsought to present the newest discoveries in lightning research, based on validphysical concepts. A recent book on lightning by Rakov and Uman1 serves as anexcellent reference, presenting data obtained through the last three decades from theentire field of lightning research. However, that book does not include any of thenewer physical concepts of lightning development. An advanced-level book writtenby two world-famous experts in the field of gas discharges in long gaps, EduardBazelyan and Yuri Raizer2, is aimed at readers with strong physics backgrounds.Long-gap gas discharges and lightning leaders share a common feature: thestreamer–leader process. This commonality has allowed the book by Bazelyanand Raizer to become a valuable contribution to the lightning literature.

1Rakov V A and Uman M A 2003 Lightning: Physics and Effects (Cambridge: Cambridge University Press)2 Bazelyan E M and Raizer Yu P 2000 Lightning Physics and Lightning Protection (Bristol: Institute of PhysicsPublishing)

xi

Unfortunately, the ambiguities and fallacies in the interpretations of lightningprocesses that have held sway and been unchallenged throughout the past severaldecades have continued to mislead lightning researchers. Historically, most of theterminology found in the lightning literature was created with little consideration(and perhaps a poor understanding) of the physical nature of the events thisterminology identified. A dramatic change occurred with the acceptance, finally,of the concept of the bidirectional, bipolar and uncharged leader, put forward since1950 by the brilliant German physicist, Heinz-Wolfram Kasemir (1910–2007). Thistheory had been considered controversial, and ignored, for many years. As oftenhappens in science and nature, however, the solutions to some difficult problemsfrequently turn out to be beautifully simple and elegant; this is the case withKasemir’s theory of the bidirectional and uncharged leader, as it is applied tolightning physics.

This book seeks to correct the glaring deficiency that exists in lightning research,specifically, the lack of an accessible presentation of the basic physics of lightningdischarges, with a focus on leaders as the key components. The challenge forresearch scientists, as I see it, is to assemble the pieces of the lightning puzzle, so thatnot only do they fit, but they also produce a coherent picture of the features presentin other manifestations of the lightning phenomenon. As a product of the electricalenvironment in thunderstorms, lightning processes are interpreted in this book, firstand foremost, by using the laws of electrostatics. This approach works well for thedevelopment of the majority of lightning processes in intra-cloud and cloud-to-ground flashes, and is supported by a multitude of convincing observations andmeasurements. The exception is the mechanism of recoil-leader formation, whichhas been interpreted by using electrodynamics and an analogy to a free burning arc.In addition, the relevance of some of the results of lightning research to the practiceof lightning protection is discussed in chapter 11.

With the recent advances in lightning physics, the need has become apparent forcorrect terminology to implement the interpretation of lightning processes.Accordingly, the terminology, used widely until just recently in the lightningliterature, and still influenced by Schonland’s outdated 1947 concept, has beencorrected in this book to agree with Kasemir’s concept.

Publications concerned with atmospheric electricity have typically been requiredto declare which of the two sign conventions is being used—that of ‘physics’ or‘atmospheric electricity’— to represent the electric field. The difference between thetwo is that they assign opposite polarities to ground-based electric field measure-ments, a practice always confusing to the reader. At the 2014 InternationalConference on Atmospheric Electricity in Norman, Oklahoma, the lightningresearch community decided unanimously to standardize usage of the so-called‘physics’ sign convention in the lightning literature. That convention is used in thisbook. When records from other, earlier publications made using the atmosphericelectricity sign convention are included in the book, a comment will be added to thefigure caption.

What is not in this book? In order to avoid redundancy with the literature thatcurrently exists, this book does not present all the published data about lightning;

Principles of Lightning Physics

xii

that information may be readily found in Uman3, and in Rakov and Uman1.Neither does this book address the separate topic of thunder; for this, interestedreaders can refer to chapter 12 in Uman4, where this subject is well, andexhaustively, described. Nor does this book cover the topics of such high-energyatmospheric phenomena as blue jets, red sprites, etc, at high altitudes abovethunderstorms, because these often appear subsequent to the occurrence of lightningin thunderstorms, not as part of it. These topics are thoroughly covered by Dwyerand Uman5. Furthermore, because my book is a monograph, presenting primarilymy own research, rather than a reference book, I have been selective in referring toonly those publications essential to the material I have intended to cover.

Although, admittedly, this book is somewhat specialized, one may find it useful assupplementary reading in a university course on atmospheric electricity and light-ning. It is intended to introduce lightning physics to readers of different back-grounds, levels of experience, and knowledge, including graduate students, lightningenthusiasts, and researchers in the field of atmospheric electricity.

3Uman M A 1987 The Lightning Discharge (New York: Academic)4Uman M A 1986 All About Lightning (New York: Dover)5Dwyer J R and Uman M A 2014 The physics of lightning Phys. Rep. 534 147–241

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Acknowledgements

Writing this book has been an enormous undertaking for which I have received greatsupport and encouragement from the National Severe Storms Laboratory inNorman, Oklahoma, and its Director, Dr Steve Koch, who have made the writingof this book possible. I would also like to acknowledge the many helpful colleagues,too numerous to mention, from the lightning research community who havegraciously contributed their results to this book. Many thanks to T A Warner forhis generous permission to use his exceptional video images of lightning events forthis book. I am also extremely grateful for the more than 25 years of friendship andscientific collaboration with Dr Lothar H Ruhnke.

Finally, special gratitude goes to my dear wife, Marijo Hennagin-Mazur, the besteditor anyone could hope for, who has spent countless hours tirelessly improvingthis manuscript.

xiv

Author biography

Vladislav Mazur

Vladislav Mazur was born in 1941 in Leningrad (nowSt Petersburg), Russia, in the former USSR, during theSecond World War. His higher education includes anMS degree in Mechanical Engineering from theLeningrad Shipbuilding Institute in 1964, and an MSdegree in Electrical Engineering from the LeningradInstitute of Precise Mechanics and Optics in 1967.

Dr Mazur began his career as a lightning researcherin 1969, in the Department of ExperimentalAtmospheric Physics at the LeningradHydrometeorological Institute, where he joined a verysmall group of enthusiasts who intended to studylightning features using long-wave radars. He laterentered the PhD program in Geophysics at the sameinstitute. By 1977, Dr Mazur had completed hisdissertation on the subject of lightning studies using

long-wave radars, but was not allowed to defend it because of his plans to emigratefrom the USSR.

In 1978 Dr Mazur immigrated to the United States. In the same year, he beganhis long association with the Storm Electricity Group at the National Severe StormsLaboratory (NSSL) in Norman, Oklahoma, and worked as a Graduate ResearchAssistant at the University of Oklahoma. He received his PhD from the Universityof Oklahoma, this time in Electrical Engineering, in 1981.

From 1981 until 1984 he was a Fellow at the Cooperative Institute for MesoscaleMeteorological Studies (CIMMS) at the University of Oklahoma. In 1984 he joinedthe permanent staff at NSSL, where he still works. The experience and knowledgethat Dr Mazur had gained from studying lightning with radars led to hisparticipation in the NASA Storm Hazards Program (1982–6). This program wasinvestigating lightning interaction with aircraft. The use of UHF radar for guidingthe NASA research aircraft into thunderstorms was an approach that proved to beextremely successful in achieving the program’s objectives. During the 1980s, withthe goal of confirming the conclusions obtained in the NASA program, Dr Mazuralso collaborated closely with two other programs that were studying lightning–aircraft interaction: the US Air Force/FAA Lightning Characterization Program(1985–7) and the ONERA Transall Program in France (1988–9). He then extendedhis efforts and interest into the interpretation of the records of the numerous sensorson board the research aircraft, in an attempt to understand the physical mechanismof the aircraft-triggered lightning.

xv

In 1988, recognizing the essential role Dr Mazur had played in the researchprograms that addressed lightning–aircraft interaction, he was awarded the covetedUS Department of Commerce Gold Medal.

Understanding the processes involved in lightning initiation on a flying aircraftprovided a key to the interpretation of other features of lightning, which has becomethe central focus of Dr Mazur’s research efforts from the 1980s onward. Hisscientific collaboration with Dr Lothar H Ruhnke, a talented physicist andexperimenter, which began in the late 1980s and continued for the next 25 years,resulted in some groundbreaking discoveries, as well as the confirmation of afundamental, but controversial theory of lightning development—the concept of thebidirectional, bipolar leader advanced by Heinz-Wolfram Kasemir. This theory isnow accepted as the starting point for a full understanding of the phenomenon oflightning. During the past 30 years, Dr Mazur has promoted and applied thisconcept in his research, revising and changing outdated dogmas, and building a newfoundation for lightning physics.

Dr Mazur has applied his expertise in lightning physics to assist with lightningprotection for the National Weather Service’s (NWS) weather-radar network, andthe Federal Aviation Administration (FAA) radar installations and air trafficcontrol towers at several major airports in the United States.

Dr Mazur lives in Norman, Oklahoma with his wife of 33 years, Marijo, and histwo beloved collies.

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