fast photometric imaging of high altitude optical flashes above thunderstorms

128 Pages·2007·4.13 MB·English

FAST PHOTOMETRIC IMAGING OF HIGH ALTITUDE
OPTICAL FLASHES ABOVE THUNDERSTORMS
a dissertation
submitted to the department of applied physics
and the committee on graduate studies
of stanford university
in partial fulfillment of the requirements
for the degree of
doctor of philosophy
By
Christopher Paul Barrington-Leigh
September 2000
(cid:13)c Copyright 2001 by Christopher Paul Barrington-Leigh
All Rights Reserved
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I certify that I have read this dissertation and that in my opinion
it is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.
Umran S. Inan
(Principal Advisor)
I certify that I have read this dissertation and that in my opinion
it is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.
Sebastian Doniach
I certify that I have read this dissertation and that in my opinion
it is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.
Martin Walt
Approved for the University Committee on Graduate Studies:
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With respect for all those who have chosen less selfish pursuits than the study of upper
atmospheric physics.
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Abstract
Lightning in the Earth’s troposphere is among the largest impulsive energy sources within the
bounds of the magnetosphere, and with 50 to 100 cloud-to-ground discharges per second globally,
providesasteadysourceofelectrodynamicexcitation. Lightningeffectsonthemagnetosphereinthe
formofwhistler-modewaveshavebeenrecognizedfordecades,andwhistlersareknownalsotocause
lightning electron precipitation in the ionosphere. Recently, however, a range of spectacular and
more immediate lightning effects on the lower ionosphere and the mesosphere have been discovered.
These were first detected by very low frequency (VLF) radio remote sensing, which inspired studies
of possible optical effects at about the same time as two fortuitous discoveries in 1989 and 1990
revealed remarkable visual evidence of direct electrodynamic coupling between lightning and the
upper atmosphere [Franz et al., 1990; Boeck et al., 1992]. These new phenomena were soon to be
called “sprites” and “elves.”
A novel photometric array with a high-speed triggered data acquisition system, bore-sighted
image-intensified CCD video camera, and VLF radio receiver was built to detect a predicted sig-
nature of elves, the lower ionospheric (80 to 95 km altitude) flash due to heating by an impinging
electromagnetic pulse launched by intense lightning currents. The narrow individual photometer
fields-of-view of (2.2◦×1.1◦) provide a spatial resolution of ∼20 km at a range of 500 km, enabling
the documentation of rapid expansion occurring over a horizontal range of 200 km with a time
resolution of ∼15 µs [Inan et al., 1997].
In 1997 data acquired by the array (named the “Fly’s Eye”) settled several questions regarding
the relationship between elves and lightning and, by measuring the spatial extent of ionospheric
heatingandthefrequencyofoccurrenceofelves,demonstratedtheirsignificanceincausingsustained
and cumulative modification of the nighttime lower ionospheric electron density profile over large
thunderstorm systems [Barrington-Leigh and Inan, 1999].
The Fly’s Eye, along with a telescopic imaging system developed in 1998 [Gerken et al., 2000],
was also used to investigate sprites. Sprites are highly structured discharges lasting 5 to 100 ms
and extending from 40 to 85 km altitude which result from intense electric fields following a major
redistribution of electric charge in the troposphere — usually a positive cloud-to-ground return
stroke. Photometric, video, and radio (30 Hz to 20 kHz) measurements were used to detect the first
sprites directly associated with negative cloud-to-ground lightning, implying a breakdown process
that can propagate in upward and downward electric fields; this is consistent with only a subset
of the theoretical descriptions for sprites [Barrington-Leigh et al., 1999a]. In addition, telescopic
imageryshowsclearevidenceofbothpositiveandnegativecoronastreamerpropagationinasprite.
Detailedelectromagnetic(finitedifferencetimedomain)modelingofbothelvesandspritesisused
to interpret observations. Three events recorded by a high-speed (3000 frames per second) imaging
system in 1997, combined with modeling results, led to the recognition of a widespread confusion in
interpreting video signatures of elves and sprites and identified for the first time the diffuse upper
portion of sprites, a hard-to-measure but likely ubiquitous form of heating and ionization in the
upper mesosphere which is now called the sprite halo [Barrington-Leigh et al., 2000].
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Acknowledgements
How can I adequately thank everyone who has made the past five years the most fun period
of my life? I truly could not have asked for a better advisor. Umran has been open, thoughtful,
understanding, accessible, patient, and unendingly enthusiastic, besides his intellectual talents.
I have had especially rich interactions with Mark Stanley. Data taken while working together at
Langmuir Laboratory, as well as Mark’s own measurements analyzed collaboratively, form a major
part of the work in this dissertation. In addition, Mark’s knowledge of lightning and thunderstorm
processes were very valuable to me, and we have enjoyed many sprite-related discussions.
IamverygratefultoVictorPaskoforhisexceptionallywide-opendoorandforthemanyexciting
and illuminating discussions I’ve had with him. It has been a great privilege to be working so close
to the preeminent theorist in our field, and many of the ideas presented in this work follow from
Victor’s research and what I have learned from him.
Iwouldliketoextendthankstoanothercoauthor,SteveCummer,forhishelpwithELFcurrent
determination,forinsightfuldiscussions,fortakingmemountainbiking,andjustforhisoutstanding
contributions to this field. I am also grateful to Martin Fu¨llekrug for sharing his superb ULF data,
and for useful (email) conversations. Steve Reising has also extended valuable advice to me on
numerous occasions, for which I am very grateful.
My thanks and respect go out to Jack Winckler at the University of Minnesota for his visit and
consultation in designing the Fly’s Eye. Rick Rairden has been consistently generous and outgoing
in helping our efforts. He provided the camera each year of the Fly’s Eye operation, as well as a
calibrated light source on more than one occasion. Gary Swenson and Stephen Mende also both
contributed to the Fly’s Eye experiment through helpful discussion.
Ken Cummins of Global Atmospherics Inc. provided NLDN data, and the Astronomical Data
Center’s stellar database was used for interpreting star fields. Also, I am indebted to the Langmuir
Laboratory for excellent support and the use of their facilities.
Elizabeth Gerken fielded the telescopic imager, and operated the Fly’s Eye during observations
on 6 August 1998. I am indebted to Sean Hansen for his outstanding diligence in operation of the
juvenile Fly’s Eye during the summer of 1996.
Working in a group with such a rich history in magnetospheric physics has been a joy. Inspiring
andfascinatingdiscussionswithDonCarpenter,BobHelliwell,BillTrabucco,andmanyothersfrom
the group will remain strong in my memory. I am grateful for help from Jerry Yarbrough and from
many of the students with whom I have overlapped in the VLF group, and for the support of many
othersinthecommunity. IwouldalsoliketothankMartinWaltandSebDoniachforkindlyserving
on my reading committee.
The logistical support of Shao Lan Min and Paula Perron have each been invaluable, and I have
greatly appreciated their invariant efficiency and friendliness.
I would like to thank Peter Dourmashkin for inspiring, investing in, and believing in me during
my first year at M.I.T., and to Al Lazarus, Karolen Paularena, and the many dedicated teachers I
had there for their help and love of physics and teaching.
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I left Stanford on two occasions for highly enriching summer schools. For my time in Vienna I
amindebtedtotheCanadianFoundationfortheInternationalSpaceUniversityandalltheinspired
teachers and administrators at I.S.U., and for my time in Greenbelt I am grateful to NASA and
especially Steve Zalesak at GSFC.
In addition, my two trips to Antarctica were each fun and beautiful beyond my expectation and
dreams and I consider myself to have been superlatively fortunate in all the field work I have been
able to undertake. I shall always remember seeing my first naked-eye sprite on 27 July, 1997. My
scientific curiosity has long been founded in such natural beauty.
I have enjoyed constant love and support from Esther Mecking, my sister Rosalind, my mother
Iris, my father John, and my brothers Robert and Stephen. My family has been my biggest gift
in life. Esther has my special gratitude for encouraging me to eat and sleep regularly, and exercise
occasionally, during the six weeks prior to my defence.
IammostgratefultoallmyfriendsfromtheStanfordOutdoorEducationProgramandelsewhere
whohavehelpedtomakemylifewholeandtokeepmecognizantoftheothertwoofEdwardTeller’s
three questions. The wilds of California have been a constant inspiration; I am grateful to all those
who have helped to preserve pieces of them.
This dissertation was brought to you by Matlab, Adobe Illustrator, and software that was built
to work rather than to make money – LATEX, Emacs, NoWeb, and Gnu’s compiler for C++.
Christopher P. Barrington-Leigh
Stanford, California
September 22, 2000
This work was supported by the Office of Naval Research under grant N00014-94-1-0100 and
AASERT grant N00014-95-1-1095 and by the National Science Foundation under grant ATM-
9731170.
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