fagu98.bib
@ARTICLE{papadopoulos_fagu98,
AUTHOR = {K. Papadopoulos and G. M. Milikh and P. N Guzdar and
A. S. Sharma},
TITLE = {Gamma Rays Generation by Lightning},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F126},
MONTH = {November},
ANNOTE = {A22A-03 poster},
ABSTRACT = {A new and novel mechanism for generation of gamma
rays observed at equatorial latitude by the Gamma
Ray Observatory is proposed. Several new
interacting physics elements are involved.
-The first element is the generation of runaway
electrons by thunderstorm electric field at
altitudes 16 - 20 km slightly below the region where
the runaway electrons become magnetized ($z \sim 20)
km.
-Upward leakage of the runaways above 20 km allows
for the presence of helicon mode with frequency $f <
10 \sqrt{n_r}$ kHz where $n_r$ is the local density
in $cm^{-3}$ of the leaking electrons.
-ELF and VLF waves induced by lightning, reaching
this region undergo self-focusing creating channels
of enhanced electric field structure in the regions
of runaway leakage.
-The self-focused electric fields interact
resonantly with runaways inducing a new runaway
discharge at altitudes between 20 - 40 km
-Gamma rays are due to beams from the runaway
electrons forming at those altitudes.
A qualitative analysis will be presented. The new
process can account for significant enhancement of
energy deposited by lightning in the middle
atmosphere with significant consequences to global
warming.}
}
@ARTICLE{smith_fagu98,
AUTHOR = {D. A. Smith and D. N. Holden and X. Shao and P. R. Krehbiel},
TITLE = {Physical Characteristics of Compact Intracloud
Discharges (CIDs)},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F127},
MONTH = {November},
ANNOTE = {A22A-11 poster},
ABSTRACT = {Compact Intracloud Discharges (CIDs) are distinct,
isolated electrical discharges that occur within
intense regions of thunderstorms. Unlike other
intracloud and cloud-to-ground lightning events that
occur as sequential breakdown processes and often
last for a large fraction of a second, CIDs are
singular impulsive events that last for only a few
tens of microseconds of less.
In recent years, CIDs and the thunderstorms in which
the events have occurred have been studied using a
variety of resources including ground-based electric
field change and broadband HF arraysk, satellite
instrumentation including the Blackbeard receiver
and FORTE satellite, NEXTRAD weather surveillance
radars, and the National Lightning Detection
Network. Based on the data from these resources,
CIDs have the following physical characteristics:
CIDs begin with an initial breakdown stage as
indicated by RF radiation that lasts for a few
microseconds. Ionization proceeds at a velocity on
the order of one third of the speed of light and
forms a channel that is between a couple hundred and
many hundred meters in spatial extent. The channel
is predominately GET abstract from AGU site..}
}
@ARTICLE{krehbiel_fagu98,
AUTHOR = {P. R. Krehbiel and R. Thomas and W. Rison and
T. Hamlin and J. Harlin and M. Davis},
TITLE = {Lightning Mapping Observations During {MEaPRS} in
Central {O}klahoma},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F127},
MONTH = {November},
ANNOTE = {A22A-12 poster},
ABSTRACT = {A 3-dimensional lightning mapping system was operated
over a county-wide area northwest of Oklahoma City in
conjunction with the MEaPRS project during June of 1998.
Observations were obtained of the total lightning activity in
several supercell storms, a tornadic storm, and storms having
a large fraction of positive cloud-to-ground lightning. A
large, fast-moving storm system that propagated over the
network produced normal cloud-to-ground (CG) and intracloud
(IC) lightning discharges in a number of coexisting cells and
occasional discharges of large horizontal extent. One hybrid
IC/CG flash had an overall extent of 75 km and exhibited a
bilevel structure in the main negative and upper positive
charge regions of the storm. The channels in the upper
positive charge region decreased to the altitude of the main
negative charge as the discharge progressed into an apparent
stratiform region away from the core of the storm, indicating
that the positive charge region similarly decreased in
altitude. A third, slightly lower level of activity was also
observed that may be associated with lower positive charge.
Lightning in the supercell storms was essentially continuous
and had a more amorphous structure, with discharges occurring
in rapid succession at different locations that filled the
horizontal area of the storm every minute. Preliminary
results for one predominantly positive CG storm showed that
+CG discharges were associated with normal polarity IC
discharges early in the storm, but that later in the storm's
evolution the IC flashes appeared to be of inverted polarity,
that is, between an upper negative and main positive charge
region. The latter result remains to be confirmed by
electrostatic field change observations. Lightning in the
tornadic storms remains to be analyzed. Overall, the great
plains storms are observed to be extremely active
electrically.}
}
@ARTICLE{rison_fagu98,
AUTHOR = {W. Rison and P. R. Krehbiel and M. Davis and
T. Hamlin and J. Harlin and T. Barber and M. Jones},
TITLE = {A Deployable 3-Dimensional Lightning Mapping System},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F127},
MONTH = {November},
ANNOTE = {A22A-13 poster},
ABSTRACT = {A lightning mapping system based on Kennedy Space
Center's real-time LDAR (Lightning Detection and Ranging)
system has been developed that utilizes GPS timing at a number
of widely spaced locations to image lightning discharges in
three spatial dimensions and time. The system was
successfully deployed in two field programs in 1998 -- in
central Oklahoma during May and June and in central New Mexico
during August and September. Lightning-produced radiation
signals are received in an unused television channel (Channel
3, 60--66 MHz) and the time of arrival of impulsive events is
independently measured at each station using the GPS timing
signals. Overall timing accuracies of 40--50 ns rms are
achieved on actual lightning events, corresponding typically
to 50--150 m location errors. In the 1998 field programs, the
peak VHF radiation signal was timed in successive 100~$\mu$s
windows at 10 locations over a 50-km diameter area. This
provided excellent location information over a 100-km diameter
area and useful information out to several hundred km (with
increasing errors at larger distances). An automatic,
non-linear least squares solution procedure is used to locate
the radiation sources and provides reliable locations when an
event is observed at 6 or more stations. The system typically
locates 500--1000 sources per second of lightning activity.
3600 sources were located during one horizontally extensive
flash that lasted 2.5 seconds. The sources clearly show the
temporal development and channel structure of lightning
flashes and sometimes the dendritic structure as well. The
system has been designed to be relatively low cost and is
PC-based, using a custom programmable-logic PC card to
digitize and time the signals. A wireless communications
network (with 115~kbaud data rate for each remote station) is
currently being used to control the network and will be used
to automatically transmit data to a central site for real time
processing and display of the locations. Electric field
change and field mill sensors will also be added at each site
to further characterize the lightning and the storm
electrification.}
}
@ARTICLE{symbalisty_fagu98,
AUTHOR = {E. M. D. Symbalisty and R. A. Roussel-Dupr{\'{e}} and
V. A. Yukhimuk},
TITLE = {The Transition From Red Sprite to Columniform Sprite
in the Context of Runaway Air Breakdown Theory},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F129},
MONTH = {November},
ANNOTE = {A22A-26 poster},
ABSTRACT = {The results of numerical simulations of columniform
sprites, in the context of the runaway air breakdown mechanism
(A. V. Gurevich, G. M. Milikh, and R. Roussel-Dupré, {\it
Phys. Lett. A}, {\bf 165}, 463, 1992), are presented. The
results include intensity and spectra of optical emissions,
and the time dependent secondary (slow) and primary
(relativistic) electron concentrations. We recall that the
simulations model the transient electrical environment above a
large mesoscale thunderstorm complex due to a normal lightning
stroke. The transition from a normal sprite discharge to a
columniform sprite is proposed to be a function of the
configuration of the driving electric field. In our 2-D,
axi-symmetric simulations, with simple models for the driving
fields, we can produce the transition by varying the strength,
location, and spatial size of the initiating positive cloud to
ground lightning stroke. For example, a point discharge
(spatial size less than 1 km) is more likely to produce a
columniform sprite than a spatially extended lightning
discharge, with all other parameters being equal. We are using
the recently recalculated runaway avalanche rates
(E. M. D. Symbalisty,R. Roussel-Dupré, and V. Yukhimuk, {\it
IEEE Transactions on Plasma Science}, scheduled to appear in
October 1998 issue). We also examine the impact of different
ambient electrical conductivity profiles and compare our
results to observations (E. M. Wescott, D. D. Sentman,
M. J. Heavner, D. L. Hampton, and W. A. Lyons, {\it University
of Alaska Preprint}, 1997).}
}
@ARTICLE{lyons_fagu98,
AUTHOR = {W. A. Lyons and T. E. Nelson and E. R. Williams and
J. A. Cramer and T. R. Turner},
TITLE = {Changes in the Electrical Structure of
{U}. {S}. Thunderstorms Ingesting Smoke from the 1998
{M}exican Fires},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F129},
MONTH = {November},
ANNOTE = {A22B-02 poster},
ABSTRACT = {As well documented by both satellite imagery and surface
aerosol concentration measurements, smoke from the vast
1998 El-Nino drought-related forest fires in Mexico and
Central America frequently advected into the United States.
Specifically, between about 7 April to 8 June, most air
masses over the southern plains of the U.S. were influenced
by the smoke. A strong frontal zone crossing the region
between 14 - 18 May resulted in smoke being advected as far
north as Ontario and eastward to New England. As documented
by the National Lighting Detection Network (NLDN),
thunderstorms developing within these contaminated air
masses had extraordinary changes in their electrical
characteristics. Specifically, large thunderstorm systems
exhibited very high percentages of cloud-to-ground (CG)
lightning flashes with positive polarity (+CGs). While +CGs
are typically less than 10% of the total, many affected
storms, such as those with the mid-May frontal system,
sustained +CG percentages of 50 to 90\% during their lifetime.
Moreover, the peak currents within these +CGs were much
higher than normal. Throughout a two month period, storms
in the southern plains averaged three times the normal
frequency of +CGs and twice the average peak current. Prior
research suggests +CGs have far greater potential for
starting fires, disrupting electrical systems, and possibly
producing larger amounts of NOx. It has been confirmed that
lightning from the 1998 smoke-influenced storms produced
unprecedentedly large numbers of optical sprites in the
mesosphere. Similar though less pronounced +CG enhancements
may have been observed in Florida sea breeze thunderstorms
during that state's siege of summer wildfires. Some possible
mechanisms which might explain these unexpected changes will
be presented.}
}
@ARTICLE{nelson_fagu98,
AUTHOR = {T. E. Nelson and W. A. Lyons and R. A. Armstrong and
E. R. Williams and D. M. Suszcynsky and R. Strabley
and M. Taylor and L. Gardner},
TITLE = {Some Initial Results from {SPRITES}'98},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F135},
MONTH = {November},
ANNOTE = {A31A-01 poster},
ABSTRACT = {SPRITES'98 was conducted at the Yucca Ridge Field
Station near Fort Collins, CO from mid-May through August
1998. Using multiple remote sensing technologies, coordinated
measurements of individual sprite and elve events were
obtained. Both red and blue low-light imagers (LLTVs) and
multi-color broad- and narrow-band photometers monitored
optical emissions. Evidence of ionization within sprites
obtained in previous programs was confirmed from simultaneous
4278 and 4709 nm emissions. High speed (1000 fps) images of
sprites reveal new details of the temporal sequence of
events. In addition, numerous high speed videos of the entire
CG lightning event for both positive and negative polarity
strokes provide new insights on the continuing currents and
horizontal dendrite discharges. These videos were coordinated
with optical measurements made with a photodiode array plus
VLF and ELF transients (Q-bursts) made at MIT's Rhode Island
Schumann resonance observatory. Storms ingesting smoke from
Mexican fires produced unprecedentedly high percentages of
+CGs, which in turn had twice the normal peak currents. A
record number of sprites (nearly 400 in 208 minutes) were
imaged above one such smoke-influenced storm. Sprites again
were typically associated with storms with radar echoes larger
than 10,000 km2, but some exceptions were noted, especially
bursts of sprites in the dying phases of some supercell class
thunderstorms. An unusual interaction between a meteor and a
sprite was recorded. Monitoring was also coordinated with
scientists from Tohoku University, New Mexico Tech, Stanford,
and the University of Alaska.}
}
@ARTICLE{strabley_fag98,
AUTHOR = {R. Strabley and D. M. Suszcynsky and
R. Roussel-Dupre and E. M. D. Symbalisty and
R. A. Armstrong and W. A. Lyons and T. A. Nelson},
TITLE = {Video and Photometric Observations of a Possible
Metor-Triggered Sprite/Jet Event},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F135},
MONTH = {November},
ANNOTE = {A31A-02 poster},
ABSTRACT = {This paper presents video and photometry data of a possible
meteor-triggered sprite/jet event. The data was recorded
with both white-light and blue-light Xybion video cameras
with millisecond time-stamping, a gps time-tagged broadband
red photometer with 50 microsecond time resolution, and a VLF
receiver. The event was collected on August 1, 1998 during
the SPRITES '98 campaign at Yucca Ridge Field Station
operated by FMA Research in Ft. Collins, CO. The event
consisted of three stages, (1) the observation of a
moderately bright meteor, (2) the development of a sprite in
the immediate vicinity of the meteor as the meteor reached
the 60 - 70 km altitude range, and (3) a slower forming ``jet''
of luminosity that appeared during the late stages of the
sprite and propagated back up the ionization trail of the
meteor. The event is analyzed in terms of its geometry, its
association with the meteor, and the implications to existing
theories for sprite and jet formation.}
}
@ARTICLE{rairden_fagu98,
AUTHOR = {Rick Rairden and Stephen Mende},
TITLE = {Intensity-Calibrated Sprite Observations from New Mexico},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F135},
MONTH = {November},
ANNOTE = {A31A-03 poster},
ABSTRACT = {Image intensified video cameras fielded at the Langmuir
Laboratory near Socorro NM recorded numerous Sprite events
during the summer 1998 campaign. The Lockheed Martin/UC
Berkeley effort involved field testing of a new CID camera,
and ground-based trials of a NASA camera, veteran of the Space
Shuttle Tethered Satellite missions. Calibrated intensity
results will be presented for white light and red-filtered
imagery obtained July 19-22.}
}
@ARTICLE{hardman_fagu98,
AUTHOR = {Simon F. Hardman and Richard L. Dowden and James
B. Brundell and John L. Bahr and Zenichiro Kawasaki
and Craig J. Rodger},
TITLE = {Sprites in {A}ustralia's {N}orthern {T}erritory},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F135},
MONTH = {November},
ANNOTE = {A31A-04 poster},
ABSTRACT = {Sprites have been observed near Darwin in Australia's
Northern Territory (NT). These are the first confirmed ground
observations of sprites outside America. The spatial and
temporal properties of sprites seen in the NT are similar to
those measured in the United States. A number of 'dancing
sprites' were observed, where a succession of sprite columns
form and decay, appearing to move across the sky. On one
night almost all the NT dancing sprites progressed from right
to left, or towards a more southerly bearing, suggesting that
the direction of dancing sprite movement is determined by
large scale cloud structure.}
}
@ARTICLE{fullekrug_fagu98,
AUTHOR = {Martin Fullekr\"ug},
TITLE = {{ULF/ELF} Magnetic Fields of Sprite-Associated
Lightning Flashes},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F135},
MONTH = {November},
ANNOTE = {A31A-05 poster},
ABSTRACT = {During the sprite campaign 1998, the Institut f\"{u}r
Meteorologie und Geophysik at the Universit\"{a}t
Frankfurt/Germany deployed a network of 3
instruments to measure horizontal magnetic
field variations of sprite-associated lightning flashes
at ULF/ELF frequencies ranging from 0.01 Hz to 1 kHz.
The measurement instruments are
located in Santa Cruz/California, Socorro/New Mexico and
Saskatoon/Canada.
The network is
GPS time synchronized with an accuracy of 20 usec
between stations and enables the
triangulation of lightning flashes with continuing current
by use of time of arrival difference techniques.
The slow tails of sprite-associated lightning flashes
are often associated
with slowly varying magnetic fields on the order
of 100-200 ms which are extremely efficient in the
excitation of globally observable Earth-ionosphere
cavity resonances. The measurments at three different
stations are interpreted as quasi-static magnetic fields
of sprite-associated currents and
physical properties of these currents will be derived.
Some of the sprite-associated lightning flashes
exhibit additional
occurrences of ultra-slow tails in the Pc1 frequency range
\mbox{(0.2-5.0 Hz)}.
The measurements at three different stations are used to
quantify the directional dependence
of ultra-slow tails along and across the
magnetic field lines and
an interpretion in terms of discrete
excitations of ionospheric Alfven resonances
will be discussed.}
}
@ARTICLE{huang_fag98,
AUTHOR = {E. W. Huang and E. R. Williams R. A. Boldi and
S. J. Heckman and W. A. Lyons and T. E. Nelson and
M. J. Taylor and C. T. Wong},
TITLE = {Criteria for Sprites and Elves based on {S}chumann
{R}esonance Observations},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F135},
MONTH = {November},
ANNOTE = {A31A-06 poster},
ABSTRACT = {Ground flashes with positive polarity associated with
both sprites and elves excite the Earth's Schumann resonances
to amplitudes several times greater than the background
resonances. Theoretical predictions for dielectric breakdown
in the mesosphere are tested using ELF methods to evaluate
vertical charge moments of positive ground flashes.
Comparisons of the measured time constants for lightning
charge transfer with the electrostatic relaxation time at
altitudes of nighttime sprite initiation (50--70~km) generally
validate the electrostatic assumption of predictions made
initially by C.T.R. Wilson. The measured charge moments
(200--2000~C-km) are large in comparison with ordinary
negative lightning, but are insufficient to account for
conventional air breakdown at sprite altitudes. The measured
charge moments however are sufficient to account for electron
runaway breakdown, and the long avalanche length in this
mechanism also accounts for the exclusive association of
sprites with ground flashes of positive polarity. The
association of elves with large peak currents (50--200~kA)
measured by the National Lightning Detection Network in a
bandpass beyond the Schumann resonance range is consistent
with an EMP mechanism for these events.}
}
@ARTICLE{satori_fag98,
AUTHOR = {G. Satori},
TITLE = {El Nino Related Variations of Global Lightning
Activity as Shown by Schumann Resonances},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-07 poster},
ABSTRACT = {Schumann resonance (SR) frequencies and amplitudes
have been recorded for the vertical electric
component at Nagycenk Observatory in Hungary since
May of 1993. The excitation source of SR is the
global lightning activity which is responsive to
surface air temperature. The SR frequencies are
indicative to the areal extension of global
lightning activity and the variations of source-
receiver geometry, as well as to the speed of
north-south annual migration of thunderstorm
regions. All these parameters exhibit El Nino
related variations as shown by SR observations.
The north-south asymmetry of the land/ocean
ratio plays an important role in the El Nino
related redistribution of the temperature
dependent global lightning activity. }
}
@ARTICLE{schlegel_fagu98,
AUTHOR = {K. Schlegel and M. Full\"ekrug},
TITLE = {Changes of {S}chumann-{R}esonance Parameters During
High energy Solar PArticle Events},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-08 poster},
ABSTRACT = {Regular Mail}
}
@ARTICLE{woodard_fagu98,
AUTHOR = {R. Woodard and M. J. Heavner and D. R. Moudry and
D. D. Sentman and E. M. Wescott and J. S. Morrill
and C. Siefring and E. J. Bucsela and D. L. Osborne
and J. T. Desroschers and H. Nielsen and J. Winick
and J. Kristl and T. Hudson and L. M. Peticolas and
V. Besser},
TITLE = {Spatial Variation of Ion and Neutral Emissions in Sprites},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-09 poster},
ABSTRACT = {The EXL98 aircraft observations included both
broadband cameras and narrowly filtered cameras.
The paper will present a comparison between a camera
with response such that it primarily measures
spatial molecular nitrogen first positive (neutral)
emissions and a camera filtered for 427.8 nm ionized
molecular nitrogen first negative emissions. The
comparison of the spatial region of neutral
emissions to the spatial region of ionized emissions
is a crucial issue for estimations of the total
energy of sprites. A wide range of variability
between the two cameras has been observed. An
example of a sprite which looks almost identical in
the two systems will be presented, and an example of
a sprite which appears in the broadband camera but
not in the 427.8 nm camera will also be presented.
In addition to several examples of sprites observed
in both camera systems, a detailed analysis of the
responses of the two systems will be presented.}
}
@ARTICLE{moudry_fagu98,
AUTHOR = {D. R. Moudry and M. J. Heavner and D. D. Sentman and
E. M. Wescott and J. S. Morrill and C. Siefring},
TITLE = {Morphology of Sprites},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-10 poster},
ABSTRACT = {The currently documented forms of sprites span the range from
rather simple columniform sprites (c-sprites) in the form
of vertical lines to much more complex forms. Some are
popularly referred to as ``carrot-shaped'' sprites, as
``wishbone'' sprites, or as ``dancing sprites'', where one
sprite is followed several ms later by another, then another.
In addition, within the sprite structures, more intense
balls and branches of illumination are sometimes visible.
This study looks at the data gathered by University of
Alaska in the summers of 1995, 1996 and 1998, and attempts
to categorize sprite structures by their shape from the
simplest to the most complex forms. This work builds on the
preliminary morphology study done by Desrochers, EOS
Supplement, 76, 46, November, 1995.}
}
@ARTICLE{osborne_fagu98,
AUTHOR = {D. L. Osborne and J. Tobolski and D. Sentman and
E. Wescott and J. Winick and C. Siefring},
TITLE = {The {EXL}98 Aircraft},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-11 poster},
ABSTRACT = {Airborne measurements of sprites, jets, and other middle
and upper atmospheric electrical effects of lightning permit
diagnoses of spectral regions not accessible from the ground
because of atmospheric absorption and scattering, as well as
giving direct visual access to the associated thundercloud
tops in certain flight profiles. The EXL98 project utilized a
Gulfstream 2 business class jet aircraft to study sprites from
flight altitudes of 12 to 13.5 km. The aircraft carried a
suite of 8 separate co-aligned low light level television
imaging systems with spectral responses covering a wide range
of wavelengths 340 nm to 4.3 microns. In this paper we
describe these instruments and the corresponding optical
requirements for the aircraft viewing ports. The aircraft
structural and power engineering and safety issues involved in
creating the EXL98 aircraft are discussed, along with the
challenges they presented for performing instrument
integration, in a medium altitude aircraft environment, which
must be compliant with Federal Aviation Administration (FAA)
regulations. We describe the Global Positioning Satellite
(GPS) technology that was utilized to provide both in-flight
synchronization of the aircraft television systems, and
synchronization of the aircraft instruments with University of
Alaska ground imaging systems on Mt. Evans, CO and Jelm
Mountain, WY. }
}
@ARTICLE{benesch_fagu98,
AUTHOR = {W. M. Benesch and J. S. Morrill and C. Siefring and
E. J. Bucsela and J. H. Bowels and M. J. Heavner
and D. R. Moudry and D. D. Sentman and E. M. Wescott
and D. L. Osborne and J. T. Desrochers and
H. Nielsen and L. M. Peticolas and J. Winick and
J. Kristl and T. Hudson},
TITLE = {Overview of {NUV} Observations During {EXL} 98},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-12 poster},
ABSTRACT = {During the recent EXL 98 mission to observe sprites and other
related phenomena from aircraft, some of the video cameras
were configured to make narrow band and spectral observations
of emissions in the near ultra-violet (NUV) and blue spectral
region(~3200 - 5000$\AA$). The spectral features in this region
are primarily due to emissions from neutral and ionized
states of N$_{2}$, namely the 2PG and 1NG band systems. The need
for aircraft observations arises from the effect of
atmospheric attenuation in this spectral region when
observations are made from lower altitudes and longer slant
paths. These images and spectra will be used to estimate
electron energies as well as examine sprite morphology. In
this presentation, we will discuss NUV/Blue measurement
philosophy and motivation, the details of the instrumental
techniques and present a variety of observations made during
the EXL 98 mission.}
}
@ARTICLE{green_fagu98p,
AUTHOR = {B. D. Green and W. T. Rawlins and M. E. Fraser},
TITLE = {Kinetics of Excitation of Infrared Fluorescence by Sprites},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-13 poster},
ABSTRACT = {Regular Mail}
}
@ARTICLE{siefring_fagu98,
AUTHOR = {C. L. Siefring and P. A. Bernhardt and J. S. Morrill
and D. D. Sentman and E. M. Wescott and
M. J. Heavner and D. L. Osborne and E. J. Bucsela},
TITLE = {Correlation Between Ambient Near InfraRed ({NIR})
Airglow and Sprite Structures},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-14 poster (moved to talk?)},
ABSTRACT = {An Indium-Gallium Arsinide (INGAAS) NIR camera (spectral
range 900 and 1700 nm) was flown on the EXL98 missions to
monitor hydroxyl airglow which gives indications of density
structures in the neutral atmosphere, i.e., gravity waves.
The sensitivity of the NIR camera combined with the brightness
of the airglow in the NIR, and the fact that the camera was
operated from an airborne platform at low elevation angles,
makes these observations quite unique. These airglow
observations span a much greater altitude range than is
typical for ground based visible or NIR measurements. The NIR
experiment was extremely successful and made the first
measurements of NIR emissions from Sprites. Also of
importance are cases where a clear correlation was seen
between structures in the neutral density and the
shape-and-form of Sprite emissions (both in the visible and
the NIR). In a number of cases the terminal altitude and
bright and dark bands in the Sprites where aligned with the
ambient airglow. Also the characteristic tilt of the Sprites
was often aligned perpendicular to gravity wave fronts. We
will discuss these observations and their implications, e.g.,
these observations would appear to support 'classical'
breakdown mechanisms as opposed to a runaway breakdown
mechanism.
*The work at NRL was sponsored by NASA and ONR.}
}
@ARTICLE{deehr_fagu98,
AUTHOR = {C. S. Deehr and E. M. Wescott and D. D. Sentman and
H. C. Stenbaek-Nielsen and M. J. Heavner and
D. R. Moudry and C. L. Siefring and J. S. Morrill
and E. J. Bucsela},
TITLE = {New Evidence for Ionization of Blue Starters and
Blue Jets},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F136},
MONTH = {November},
ANNOTE = {A31A-15 poster},
ABSTRACT = {Blue jets and blue starters were first documented by
1994 aircraft observations of a severe storm near Texarkana,
Arkansas. They appear to propagate upward out of the top of
thunderstorms at speeds of order 100 km/sec. Blue jets
propagate up to about 40 km but blue starters, which resemble
blue jets, terminate abruptly after only a few km of upward
travel. Single blue jets or starters have been recorded from
aircraft near Kansas and Central America. During the EXL98
aircraft observations of July 1998, numerous blue starters
were recorded on two evenings over severe storms in the upper
Midwest. We have previously presented evidence from color TV
images of blue jets and starters that suggested that the blue
light must have an ionized N2 component. The 1998 observations
included both white light, 427.8 nm (N2+1N) and 340 nm N2 2PG
band filtered images. The 427.8 nm filter was carefully
designed to exclude the N2 2PG band emissions at 426.8 nm.
The 340 nm images show that the blue starters are not upward
lightning flashes. The 427.8 nm data clearly demonstrate that
the blue starters are ionized, and by association that blue
jets are also ionized beams. The knowledge of the ionization
allows a better estimate of the energy involved and effects on
the upper atmosphere by these phenomena. We compare the
lightning activity and hail in the 1998 storms with the
previous observations and conclusions.}
}
@ARTICLE{gerken_fagu98,
AUTHOR = {E. A. Gerken and U. S. Inan and
C. P. Barrington-Leigh and M. Stanley},
TITLE = {Results from a New Telescopic Imager: A Survey of
Sprite Structures},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F137},
MONTH = {November},
ANNOTE = {A31A-16},
ABSTRACT = {Two intensified CCD video cameras were coupled with a 40
cm aperture Newtonian telescope with a Dobsonian mount to
create a new, high-resolution sprite imager, called the
Dobsonian Sprite Experiment (DSE). The two cameras of the DSE
have fields of view of $0.92^\circ\times 0.7^\circ$ and
$12^\circ\times9^\circ$ to allow both a broad view of each
sprite and detailed imagery of one region. The experiment was
fielded during July and August, 1998 at the Langmuir
Laboratory for Atmospheric Research near Socorro, New
Mexico. Simultaneous Very Low Frequency and Extremely Low
Frequency magnetic field recordings were made at Langmuir and
at Stanford, California. During this period many sprites were
observed at ranges of up to 900 km. This paper reports on the
morphology of observed sprites, their association with storm
activity and sferic waveforms, and the variety of fine
structure observed in the telescopic imager.}
}
@ARTICLE{remick_fagu98,
AUTHOR = {K. J. Remick and D. D. Sentman and E. M. Wescott and
M. J. Heavner and D. R. Moudry},
TITLE = {Small Scale Strcture in Sprite Tendrils},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F137},
MONTH = {November},
ANNOTE = {A31A-17 poster (withdrawn)},
ABSTRACT = {High resolution images of sprites reveal that they often
possess a tendril structure attached to a much brighter main
body at higher altitude. When they are present the tendrils
originate at altitudes of about 60-65 km, extend downward to
45-50 km and exhibit a variety of structural detail and scale
sizes, from wispy and barely discernible forms to narrow,
straight or curved channels, or forked lightning-like fractal
patterns. To date the University of Alaska video imagers
have resolved this structure to a few tens of meters. In
this talk we roughly categorize the various structures using
a topological metric applied to images obtained during
various University of Alaska ground and aircraft field
campaigns, taking into account the image resolution and
effective point spread function of the camera systems derived
from stellar images. Results of this analysis are used to
assign an effective cross section to the tendrils at given
altitudes, thereby permitting improved estimates to be made
of the optical emissivity of the tendrils compared to
previous estimates based on the overall dimensions of
sprites.}
}
@ARTICLE{sukhorukov_fagu98,
AUTHOR = {A. I. Sukhorukov and P. Stubbe},
TITLE = {{QT} whistler excitation by strong lightning},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F137},
MONTH = {November},
ANNOTE = {A31A-18 poster},
ABSTRACT = {We propose that, in addition to the conventional
quasi--longitudinal (QL) whistlers, the sprite/elves
triggered lightning can produce the quasi--transversal
(QT) whistlers, a mode which does not appear in the
linear Earth--ionosphere transmission. The source of
the excitation is the small--scale nonlinear transient
current in the D-E regions, associated with fine
structure of sprite/elves--discharges. An analytical
excitation model is presented. The QT mode has a number
of peculiar signatures, such as a large $E_\parallel$
component accelerating electrons along the geomagnetic
field, strong link to the lower hybrid resonance, much
smaller dispersion at frequencies $\omega \gg \omega_{LH}$
and larger group velocities than those of the QL whistler. }
}
@ARTICLE{levtov_fagu98,
AUTHOR = {S. J. Lev-Tov and U. S. Inan and T. F. Bell},
TITLE = {Possible Mechanisms of ``Early/fast'' {VLF} events
caused by lightning},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F137},
MONTH = {November},
ANNOTE = {A31A-19 poster},
ABSTRACT = {Subionospheric very low frequency (VLF) waves provide a
powerful remote sensing tool for detection of changes in the
lower nighttime ionosphere. For example, changes in D-region
electron density or temperature are manifested in changes in
VLF wave amplitude and phase. One class of events in which
the wave amplitude and phase change in a very unique manner
is the so-called ``early/fast'' VLF events. Early/fast events
were first recognized fifteen years ago and are clearly
associated with lightning discharges. They are ``early'' in
that they occur within 20ms of the causative lightning
discharges; and they are ``fast'' in that the VLF signal change
takes place over about 20ms. In recent years, some of these
events have been found to be associated with sprites.
Although several physical mechanisms of VLF early/fast events
have been put forth, none of these has reproduced the
magnitude of some of the larger signal changes observed in
early/fast VLF events. In this paper we analyze new data
sets of ``early/fast'' events with and without sprites. We
also explore possible mechanisms for the production of the
early/fast event through conductivity changes in the
ionospheric region overhead the causative lightning (and, if
present, sprites). Sophisticated three-dimensional
subionospheric VLF propagation and scattering routines are
used to quantitatively interpret effects of possible
ionospheric profiles causing early/fast events.}
}
@ARTICLE{dowden_fagu98,
AUTHOR = {R. D. Dowden and J. B. Brundell and M. A. Cliverd
and C. J. Rodger},
TITLE = {Decay Rates of the Perturbation Phasors of Low and
High Latitude Trimpis},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F137},
MONTH = {November},
ANNOTE = {A31A-20 poster},
ABSTRACT = {Sprite-associated amplitude and phase perturbations of
subionospheric VLF transmissions (``Trimpis'') logged as a
function of time can be transformed to scattered amplitude and
phase versus time by simple phasor subtraction of the
unperturbed phasor. The form of the scattered amplitude decay
with time is related to the form of the plasma decay rate with
respect to altitude. Over the range of at least 50 km to 80
km, attachment is the dominant loss term so at any altitude
the plasma decays exponentially with time. Neglecting a small
temperature dependence, the attachment coefficient is
proportional to the square of the neutral number density and
so the decay rate decreases exponentially with a scale height
of 3.5 km. The reflection coefficient of sprite plasma at VLF
is a strong function of plasma density only near a
``threshold'' value. Thus contributions to the total scattered
VLF signal from plasma at altitudes below where the plasma
density is instantaneously passing through this threshold
value are negligible, while contributions from higher
altitudes are still as large as they have been since plasma
formation. This transition in reflection coefficient from
essentially unity to essentially zero occurs over only a few
km.
Here we examine very strong Trimpis of high signal/noise ratio
(SNR) of two types. The Type 1 Trimpis we examined were
``fast'', occurred on entirely tropical paths, from NWC (21
deg, 48' S, 114 deg, 9' E) to Darwin area (12 deg, 26' S, 130
deg, 59' E) during the lightning season and were associated
with sprites. We assume that these were produced by sprite
plasma. The Type 2 Trimpis were observed at Faraday and
Rothera, Antarctica, on both NAA (44 deg, 39' N, 67 deg, 17'
W) and NPM (21 deg, 25' N, 158 deg, 9' W). From this we
deduced that the scatter (or perturbing) source for these Type
2 Trimpis was near Antarctica in a region devoid of lightning
(and presumably of sprites) and so produced by electron
precipitation.
For both types, the rate of exponential decay decreased with
time. From the form of this decay we deduced that the plasma
extends down from the base of the ionosphere to at least 60 km
in the case of Type 1 Trimpis and to about 75 km in the case
of Type 2 Trimpis. }
}
@ARTICLE{miyamura_fagu98,
AUTHOR = {K. Miyamura and I. Nagano and S. Yagitani and
B. Barnum and R. H. Holzworth and M. C. Kelly},
TITLE = {Wave forms of lightning-generated {VLF} waves:
{C}omparison between a full-wave analysis and rocket
measurements},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F137},
MONTH = {November},
ANNOTE = {A31A-21 poster},
ABSTRACT = {A new full-wave technique has been developed to
rigorously compute space and time evolution of an ELF/VLF
electromagnetic wave in the ionosphere radiated from a current
source located above the ground. We can examine detailed wave
forms as well as dynamic spectra of the linear electromagnetic
wave fields at an arbitrary location in a horizontally
stratified ionosphere. This technique has been applied to
study propagation of VLF waves generated by various kinds of
lightning strokes modeled with transmission line currents,
especially to examine their role in generation of luminous
emissions above lightning such as Sprites and Elves.
By using the full-wave technique in this study we investigate
in detail space and time evolution of lightning-generated VLF
electromagnetic fields in the ionosphere, to discuss their
linear propagation characteristics. The computed VLF wave
forms are directly compared with those actually measured over
thunderclouds by the Thunderstorm-III rocket launched from
Wallops Island. This enables us to estimate possible
magnitude and shape of lightning strokes which generated the
VLF waves measured onboard the rocket. Quantitative
examination of amplitudes and phases of those wave forms would
even clarify nonlinear response of the ionosphere to an
extremely intense VLF wave generated by a strong lightning
stroke.}
}
@ARTICLE{veronis_fagu98,
AUTHOR = {G. Veronis and V. P. Pasko and U. S. Inan},
TITLE = {Characteristics of Mesospheric Optical Flashes
(Elves) Produced by Lightning Discharges},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F137},
MONTH = {November},
ANNOTE = {A31A-22 poster},
ABSTRACT = {A new two-dimensional cylindrically symmetric
electromagnetic model of the lightning-ionosphere
interaction includes effects of both the lightning radiated
electromagnetic pulses (EMP) and the quasi-electrostatic
(QE) fields, thus allowing effective studies of
lightning-ionosphere interactions on time scales ranging
from several $\mu$s to tens of ms. The temporal and
spatial evolution of
the electric field, lower ionospheric electron density and
optical emissions calculated with the new model are used to
theoretically investigate the effects of the lightning
return stroke current waveform (i.e., the current rise and
fall time scales) and of the observational geometry on the
optical signals observed with a photometer. For typical
lightning discharges of $\sim$100$\mu$s duration the
ionospheric response is dominated by the EMP induced heating
leading to the highly transient and laterally expanding
optical flashes known as elves. The optical signal
characteristics are found to be highly sensitive to both the
observational geometry and the current waveform. The onset
delay with respect to the lightning discharge, the duration
and the peak magnitude of optical emissions are highly
dependent on the elevation and azimuth angles of field of
view of individual photometric pixels. The shape of the
optical signal clearly reflects the source current waveform.
For a waveshape with relatively slow rise time
($\sim$50$\mu$s) a double pulse shape of the photometric
signal is observed.
}
}
@ARTICLE{rousseldupre_fagu98,
AUTHOR = {R. A. Roussel-Dupre and E. M. D. Symbalisty and V. Yukhimuk},
TITLE = {Initiation of Intra-Cloud Discharges by Runaway Air
Breakdown},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F137},
MONTH = {November},
ANNOTE = {A31A-23},
ABSTRACT = {Simulations of intra-cloud discharges initiated by
runaway air breakdown are presented. Results of new kinetic
calculations (E.M.D. Symbalisty, R. Roussel-Dupré, and
V. Yukhimuk, IEEE Transactions on Plasma Science, scheduled to
appear in October, 1998 issue) are used to characterize the
relativistic electron distribution function. Both
conventional and runaway breakdown are included in the
simulations; however, the discharge is initiated by a runaway
streamer that develops when the electric field strength
exceeds one-third the threshold for conventional breakdown.
Optical, radio-frequency, and gamma emissions are computed and
compared with existing data. Other details of the discharge
including typical temporal and spatial scales and the
development of steady-state saturation electric fields will be
discussed in the context of observations.}
}
@ARTICLE{grard_fagu98,
AUTHOR = {R. J. L. Grard},
TITLE = {The Role of Turbulence and Convection in the
Electric Charging of Thunderstorm Clouds},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F138},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31A-24 poster},
ABSTRACT = {The electric current which circulates downwards in the Earth
atmosphere results from the motion of positive and negative
ions drifting in opposite directions under the influence of
a predominantly vertical potential gradient. It is observed
experimentally that a body, such as a balloon or a gondola,
moving upwards against the electric field collects an
excess of positive ions; conversely, a falling body such
as a water drop, acquires a negative charge. This mechanism
just requires that the velocity of the body exceed that of
the drifting small ions, which is less than a few cm/s at
altitudes under 30 km in a fair weather atmosphere. In a
similar way, parcels of hot and cold air ascending or
descending in a cloud are selectively charged. Some ions
are captured by aerosol particles and form large ions which,
due to their extremely reduced mobility, are subsequently
transported with the draft against the force applied by the
electric field. Charge separation increases the ambient
electric field and current density, which in turn enhances
the charging process. This phenomenon takes place in spite of
the reduced conductivity which prevails within clouds, due to
the recombination of small positive and negative ions on
aerosol particles. The proposed mechanism is particularly
efficient during the growth phase of a thundertorm cloud,
where the air motion results essentially from rising eddies.
It is shown that, under certain conditions, the electric
field may grow exponentially from a few 10 V/m to a few 100
kV/m in a period of about 20 minutes and that a typical
thunderstorm cloud can generate a current of the order of
1 A.}
}
@ARTICLE{lehtinen_fagu98,
AUTHOR = {N. G. Lehtinen and U. S. Inan and T. F. Bell},
TITLE = {Effects of Upward Driven Runaway Electrons in the
Conjugate Hemisphere: {C}onjugate {S}prites?},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F138},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31A-25 poster},
ABSTRACT = {Runaway acceleration of relativistic electrons driven by
mesospheric quasi-static electric fields following large
positive cloud-to-ground lightning discharges has been put
forth as a possible physical mechanism for sprites and
terrestrial gamma-ray flashes. The intense and upward
propagating runaway electron beams are ultimately trapped
along the Earth's magnetic field lines and travel to the
geomagnetically conjugate region. At that point, the runaway
electron beam encounters the Earth's atmosphere and
is backscattered, producing light, ionization and x-rays,
very much like a beam of precipitating auroral electrons.
We calculate the characteristics (energy and pitch angle
distribution) of the runaway electron beam as a function
of the intensity of the parent lightning and the geomagnetic
latitude. We discuss the pitch-angle scattering of the
electrons due to beam-plasma interaction during their
propagation along the geomagnetic field line.
The backscattering of electrons, as well as optical and
x-ray emissions in the conjugate region is estimated using
the Monte Carlo approach.}
}
@ARTICLE{yukhimuk_fagu98,
AUTHOR = {V. Yukhimuk and R. Roussel-Dupre and E. Symbalisty},
TITLE = {X-ray and Radio Pulses Produced by Red Sprites, simulation
results},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F138},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31A-26 poster},
ABSTRACT = {Upward discharges driven by the runaway air breakdown
mechanism (A. V. Gurevich, G. M. Milikh, and R. Roussel-Dupré,
Phys. Lett. A, 165, 463, 1992) can generate significant x-ray
emissions as well as radio emissions. The results of numerical
simulations of the x-ray, radio and optical emissions from Red
Sprite discharge are presented. The sprite simulations are done
using the recently recalculated runaway avalanche rates
(E. M. D. Symbalisty, R. Roussel-Dupré, and V. Yukhimuk, IEEE
Transactions on Plasma Science, scheduled to appear in October 1998
issue). The x-ray emissions are generated as a result of
relativistic beam deceleration by air, their time evolution and
angle distribution are calculated taking into account the
attenuation of x-rays in the atmosphere. The radio emissions are
produced as a result of the relativistic avalanche growth and may
consist of one or two pulses. The first pulse precedes the onset of
the high altitude optical emissions and is associated with the beam
formation at lower altitude ~ 18-30 km, the source of the second
pulse approximately coincides in space and time with high altitude
optical transient. The time separation between two pulses is in
range 150 - 800 microseconds, but can appear to be different for
observers because of the spatial separation of their sources. The
results are compared with observations.}
}
@ARTICLE{barnum_fagu98,
AUTHOR = {B. H. Barnum and R. H. Holzworth and M. C. Kelley},
TITLE = {Simultaneous Ground and Rocket Based Optical
Measurements of Lightning Flashes},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F138},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31A-27 poster},
ABSTRACT = {During the Thunderstorm III rocket flight from Wallops
Island VA, during the night of September 2, 1995, simultaneous
rocket and ground based measurements were made of Cloud to
Ground (CG) and Intracloud (IC) lightning flashes. The
results of this study show that the CG triggered IC events are
much brighter at the rocket than the CG events. This is due to
the source altitude and the incloud light scattering. The
higher altitude of the IC lightning channels produce much
brighter optical signals at the rocket. The associated IC
events usually occur within 20 milliseconds of the initial CG
stroke, and initiate from near the top of the CG lightning
channel, as shown by the Wallops Island LDAR VHF system.
Because of the close timing between the CG and IC strokes,
rocket or satellite measurements can easily mistake the
brighter stroke for the actual CG lightning.
The CG and IC strokes each initiate an upgoing whistler wave
in the ionosphere, but the CG stroke typically has much
more power at lower VLF and ELF frequencies. The VLF and ELF power
spectra give a way to discern the nature of the lightning source for
space based optical sensors.
Other results of this study show that there is no
correlation between the NLDN measured peak currents and CG
stroke optical brightness for over 100 NLDN CG cases at
Wallops Island.}
}
@ARTICLE{morss_fagu98,
AUTHOR = {D. A. Morss},
TITLE = {{SPARKE} ({S}pherical {P}ropagating {A}tmospheric
{R}adiative {K}inetic {E}mission): Fireball in the
Sky?},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F138},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31A-28 poster},
ABSTRACT = {Sprite imaging using low light, image intensification
video cameras in the Omaha, Nebraska area on 22 August 1996
revealed a phenomena that was unexplained when reported at the
Dec 1996 AGU Fall meeting in San Francisco. At that time, a
number of probable causes had already been ruled out, e.g.,
space debris re-entry, meteorites, aircraft, helicopters, and
insects. Estimates of range and speed were speculated at that
time based upon the probable distances from and direction to
the nearest thunderstorms on that evening. Assuming a
thunderstorm-related initiation, it was estimated that SPARKE
seemed to have originated some 750 km away, and traveled with
a speed of approximately 3000 km/sec. Subsequent
investigation of sources and data associated with atmospheric
``lights'' included the general area of ball lightning. While
most of the reported sightings and probable mechanisms of
origin did not seem applicable to SPARKE, the reports of
microwave simulation warranted further investigation.
Consequently, tests were conducted using a small microwave
oven with a carbon source placed within the cavity. The
phenomena seen in the oven led to video capture of the
activity using the multispectral image intensification video
cameras. It then became a task of examining videos of this
observed phenomena at very slow speed to find similarities
(albeit at much reduced power and speed) to SPARKE. Given
that up-scaling the power of the microwave and sizes of the
carbon sources is not outside the bounds of reality, the
phenomena morphology observed during the microwave experiments
may similarly be possible in nature. We thus conclude that it
is entirely conceivable that the combination of events
necessary to generate SPARKE can be explained with natural
events associated with thunderstorm lightning. Details of the
experiments and images of the associations will be presented
at the conference.}
}
@ARTICLE{valdivia_fagu98_b,
AUTHOR = {Juan A. Valdivia and Gennady M. Milikh},
TITLE = {Gamma Ray Spectra due to thunderstorms},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F138},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31A-29 poster},
ABSTRACT = {Recent observations of high energy photons (x-rays,
gamma-rays),of atmospheric origin, at different altitudes have
revealed some interesting phenomena. Measurements include
balloons [Eack et al., 1997] as well as satellite observations
[Fishman et al., 1994]. These observations may provided us
with the possibility of discovering the underlying physical
process in the generation of the gamma rays. It is generally
accepted that these gamma rays are related to runaway
electrons produced by thunderstorms, but there are a number of
possible mechanism capable of producing such runaways
(Quasi-static fields, electromagnetic pulses, whislers, etc).
The objective of this report is to analyze the spatial and
temporal evolution of the spectrum of high energy photons
produced at different heights and by different initial source
distributions. This model, that include photon diffusion
(Compton scattering) and photo ionization, can be used to find
the location of the runaway source. The different models of
the generation of the runaway electrons are used to compute
the source spectrum of the high energy photons, which are then
compared with observations using the photon propagation model
described above.
Fishman et al., Science, 264, 1313, 1994.}
}
@ARTICLE{eack_fagu98,
AUTHOR = {K. B. Eack and D. Suszcynsky and W. Beasley and
W. D. Rust and R. Roussel-Dupre and E. Symbalisty},
TITLE = {A High Time-resolution balloon-borned X-ray Detector},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F138},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31A-30 poster},
ABSTRACT = {We have designed and flown a balloon-borne x-ray detector
with high time resolution to look for the existence of
runaway breakdown processes in sprites. A secondary goal
is to obtain additional data on x-ray emissions previously
observed from inside the thunderstorm, but with greater time
resolution. The x-ray spectrometer samples 3 energy bins
at a rate of 15kHz. In addition to the x-ray detector, an
electric field change instrument was also incorporated into
the package and data acquisition system to examine the
hypothesis that an electrostatic field change above a
thunderstorm complex is associated with sprites.
Although this instrument was designed with specific
sensors, the data acquisition and telemetry systems are
both much more generic allowing other sensors be used with
the existing payload design. }
}
@ARTICLE{kirkland_fagu98,
AUTHOR = {M. W. Kirkland and D. M. Suszcynsky and S. O. Knox
and R. C. Franz and J. Guillen and J. Green and
R. E. Spalding},
TITLE = {Observations of Lightning from space using the
{FORTE} photodiode Detector},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F142},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-01 talk},
ABSTRACT = {We present the initial results obtained from
observations of optical lightning activity as observed by the
Photodiode Detector (PDD) onboard the 800 km-circular,
low-earth orbiting Fast On-orbit Recording of Transient Events
(FORTÉ) satellite. The PDD is a silicon photodiode sensitive
to wavelengths from 0.4 to 1.1 microns, with a peak in the
responsivity at 0.85 microns, and having an 80° field-of-view
corresponding to a footprint diameter of approximately 1200 km
on the Earth's surface. This footprint matches that of the
Lightning Location Sensor and the 3-dB footprint of the
primary antenna connected to the RF system. In the most
frequently employed trigger mode, the PDD captures a
1.9-millisecond time history of transient optical waveforms
with 15-microsecond resolution. While optical reflections from
spacecraft or ocean surfaces do result in the detection of
false events, these false events are easily discriminated from
optical events attributed to lightning activity. We examine
the PDD data collected since launch and compare our
observations to ground-based and aircraft-based observations
of optical lightning emissions. We present examples of the
data and infer source optical energies and additional
propagation path lengths due to clouds.}
}
@ARTICLE{knox_fagu98,
AUTHOR = {Stephen O. Knox and Abram R. Jacobson and Paul Argo
and Robert Franz},
TITLE = {Correlation of {FORTE} satellite radio-frequency
lightning observations with {NLDN} stroke reports},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F142},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-02 talk},
ABSTRACT = {The FORTÉ satellite has completed a six-month (April -
September 1998) focused campaign observing lightning over
North America, in order to study the correlation (if any)
between radio-frequency emissions and very-low-frequency
sferics from lightning. FORTÉ is in a 70* inclination,
circular low-Earth orbit and makes several passes per day
within radio sight of North America.
FORTÉ records discrete records of very-high-frequency (VHF)
lightning signatures. A record typically lasts 400 microsec
and is triggered by a multichannel coincidence trigger. FORTÉ
carries a GPS clock and subsecond counter allowing 1-ms
absolute timing of registered waveforms. On the order of
ten-thousand such waveforms can be captured and downloaded per
day.
We are particularly interested in the time relationship
between FORTÉ VHF records and National Lightning Detection
Network (NLDN) stroke times. We correct the FORTÉ time-stamp
back to the putative source (indicated by NLDN stroke report
rendered with typically $<$50-microsec uncertainty), and
construct a histogram of NLDN - corrected FORTÉ timestamps. We
had expected this histogram to reveal a preponderance of FORTÉ
triggers preceding (by milliseconds to tens of milliseconds) a
cloud-ground stroke. Instead, we find that the dominant (and
perhaps only) correlation is prompt. That is, to within our
methodological uncertainty of ± 100 microsec, when a VHF burst
seen by FORTÉ is detectably coincident with an associated
NLDN-reported stroke, then the temporal coincidence is
indistinguishable from being prompt.
We will discuss these issues as well as what we mean by
detectably coincident. We will also show the characteristics
of the promptly-coincident VHF bursts and show to what extent
they differ from VHF bursts which are not associated with
sferics.}
}
@ARTICLE{argo_fagu98,
AUTHOR = {Paul E. Argo and Abram Jacobson and Matt Kirkland
and Robert Massey},
TITLE = {Initial Comparisons of Optical and Radio Frequency
Satellite Observations of Thunderstorms with Ground
Base Sferics},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F142},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-03 talk},
ABSTRACT = {The FORTE satellite, launched 29 August 1997, carries
radio-frequency-receivers for the study of lightning, as
well as fast photodiode radiometer and CCD imaging
detectors. In the first year of operations we have detected
more than 2 million radio-frequency events, and more than
one million optical events we believe to be associated with
lightning. Over the continental United States we have used
both a Los Alamos based sferics array and the National
Lightning Detection Network data to provide ground truths
for our measurements. The results are reminiscent of the
ancient story about the blind men feeling the elephant.
This is in part due to the fact that each of the detection
methods is sensitive to emissions created during different
parts of the entire lightning process. We will discuss
this, and use the multi-view perspective to help understand
more of the storm emission processes.}
}
@ARTICLE{wiens_fagu98,
AUTHOR = {Kyle C. Wiens and Robert S. Massey and Xuan-Min Shao
and Marc H. Eberle and Kenneth B. Eack},
TITLE = {The Los Alamos Electric-Field-Change Sensor Array},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F142},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-04 talk},
ABSTRACT = {We have deployed an array of electric-field-change
sensors, located in New Mexico, to help
identify the lightning processes responsible
for the VHF RF signals detected by the FORTE
satellite. The sensors are located at Los Alamos,
Socorro, Roswell, and Tucumcari. Each station consists
of a flat-plate antenna followed by an integrating
amplifier and a line driver, whose output is recorded
by a 1 MS/s 12-bit digitizer in a PC. The time
constant of the integrator is 1 ms, and waveforms
are recorded for 8 or 16 ms, with 50% or 25% pre-trigger
samples, respectively. The trigger circuit is
bipolar, and the trigger levels can be controlled
by the PC. A GPS receiver and timing card within
the PC allow time-tagging of the trigger time to
two microsecond accuracy. When taking 8-ms records,
the system can trigger on and record events
separated by as little as 30 ms for periods of several
seconds. The hard disk has a capacity of 2 GB,
which is well over 100,000 events.
The PCs run the Linux operating system, and
data and control links to Los Alamos are via
the internet. We currently download waveform
data for events that are reported (within a
1.1 ms coincidence time) by three or more stations.
Event locations are computed with a simple
time-of-arrival algorithm, and are found to
agree reasonably well with locations of events
observed by the National Lightning Detection
Network (NLDN). The array has been operational
since mid-May 1998, with very little down-time.
On active days, stations may record 30,000 or
more events, with well over 5000 events reported
by three or more stations.
Data from the array will be reported in this
and other papers in this session.}
}
@ARTICLE{shao_fagu98,
AUTHOR = {Xuan-Min Shao and David A. Smith and Kenneth B. Eack
and Robert S. Massey and Kyle C. Wiens},
TITLE = {Observations of Compact Intracloud Discharges ({CID}s)},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F143},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-05 talk},
ABSTRACT = {Data from a number of resources were used to study
thunderstorms and thunderstorm radio emissions that occurred
in the southwestern US between May and September of 1998.
These resources included the Los Alamos sferic array,
instrumentation on-board the FORT\'{E} satellite, the National
Lightning Detection Network, and pertinent NEXRAD weather
surveillance radars. The two former resources are described
in detail in other papers of this session.
A primary goal of our campaign was to study compact intracloud
discharges (CIDs), unique and isolated thunderstorm events
that have been identified as sources of narrow positive and
narrow negative bipolar electric field change pulses (NPBPs
and NNBPs), subionospheric pulse pairs (SIPPs), and
transionospheric pulse pairs (TIPPs). CIDs are powerful,
singular discharges that occur in regions of high electric
field strength and high charge density. Their physical
characteristics are described in detail in another paper of
this session.
Many hundreds of CIDs were observed by the sferic array during
the summer of 1998 and were located using methods of
differential time of arrival. Distances from the discharges
to stations of the array ranged from just a few kilometers to
many hundreds of kilometers. Source heights were determined
using relative delays between CID groundwave signals and
reflections from the earth and ionosphere. In some cases,
FORT\'{E} data were also used to determine 3-D source
locations. CID locations have been compared to those of
other thunderstorm electrical discharges and to images of
radar reflectivity. The events occur in localized regions of
thunderstorms that also produce regular intracloud and
cloud-to-ground lightning. Radar reflectivity data show that
these localized regions correspond to thunderstorm cores
where reflectivities in excess of 40 dBZ exist.
Further analysis of data from this summer should provide
insight into the following questions: Do CIDs of opposite
polarity occur at different altitudes within thunderstorms?
Do CIDs occur only in regions of high reflectivity? Do all
regions of high reflectivity produce CIDs? What are the
temporal and spatial relationships between CIDs and other
intracloud and cloud-to-ground thunderstorm electrical
discharges? Can phases of thunderstorm or different storm
types be identified as being more or less likely to produce
the events?}
}
@ARTICLE{krider_fagu98,
AUTHOR = {E. Philip Krider and Launa M. Maier and Martin
J. Murphy and Donal W. Schibert},
TITLE = {The Onset of Electrification in Florida Thunderstorms},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F143},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-06 talk},
ABSTRACT = {The NASA Kennedy Space Center (KSC) and USAF Eastern Range
(ER) currently operate a network of 31 electric field mills
(the LPLWS system), 7 VHF pulse time-of-arrival receivers
(the LDAR system), and a 5-station network of gated,
wideband magnetic direction finders (the CGLSS system) to
identify possible lightning hazards to launches and to a
variety of ground operations. The field mill data can be
used to detect the onset of cloud electrification and also
to determine the locations of any lightning-caused changes
in the thundercloud charge distribution. Previous reports
have shown that intracloud (IC) flashes tend to produce two
clusters of LDAR sources in convective storms, one typically
at 7--8 km altitude and the other at 9--10 km. The field
mill data show that the upper cluster corresponds to a
region of positive charge and the lower cluster to a region
of negative charge. The LDAR sources in cloud-to-ground
(CG) flashes tend to begin at or just below the lower edge
of the negative region and propagate downward toward a lower
positive charge region that is near the 0$\deg$C level.
During the onset of electrification, the lower positive
charge center usually appears first in the electric field
records that are close to isolated cells, i.e., the electric
field is directed downward. Later, the field reverses
polarity, and the effects of the negative charge at higher
altitude dominate the field pattern under the storm.
The implication of these results for thunderstorm
electrification and lightning warnings will be discussed.}
}
@ARTICLE{macgorman_fagu98,
AUTHOR = {D. R. Mac{G}orman and M. Stolzenburg and W. D. Rust
and T. Marshall and P. Krehbiel and R. Thomas and
W. Rison and W. Beasley and K. Eack and M. Lockwood},
TITLE = {Electric Field Profiles and Lightning in Storms with
Frequent Positive Cloud-to-Ground Lightning},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F143},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-07 talk},
ABSTRACT = {Eight balloon soundings of the electric field have been
obtained in severe storms in which the majority of ground
flashes lowered positive charge to ground, instead of the
more usual negative charge. These storms occurred in
Oklahoma, Texas, and Kansas on four different days. Two
soundings were obtained in the strong convection of
different isolated supercell storms on one day, and one was
obtained completely through the anvil of yet another
isolated storm on a second day. Two soundings were
obtained in the convective line of each of two severe squall
lines that produced mostly positive ground flashes. The
remaining sounding was in the transition region between the
convective line and stratiform region of one of these squall
lines. Preliminary analyses of the soundings are compared
with published soundings from storms that produced primarily
negative ground flashes. Cloud-to-ground lightning data
from the U.S. National Lightning Detection Network have been
analyzed for one of the isolated storms. The evolution of
positive ground flash rates relative to both radar-derived
storm parameters and severe weather was similar to that
observed by previous studies of isolated severe storms
having frequent positive ground flashes. Lightning also was
mapped in three dimensions for one of the isolated storms in
which a sounding was obtained and for several other severe
storms that occurred in central Oklahoma during field
operations. Initial analysis of mapping data for some
positive ground flashes shows that they were bilevel hybrid
flashes, each flash having two layers of extensive
horizontal intracloud structure. The layers are inferred to
correspond respectively to upper positive charge and lower
negative charge in the thunderstorm charge distribution.
Later in the storm, bilevel intracloud flashes appeared to
occur in an inverted charge distribution, with upper
channels propagating through negative charge and lower
channels propagating through positive charge. Cloud flash
rates in Oklahoma storms typically were much larger than
ground flash rates, particularly during periods when the
storms produced severe weather.}
}
@ARTICLE{thomas_fagu98,
AUTHOR = {Ronald J. Thomas and William Rison and Timothy
Hamlin and Jeremiah Harlin and Paul R. Krehbiel},
TITLE = {3-Dimensional Lightning Observations in Central New Mexico},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F143},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-08 talk},
ABSTRACT = {Following its initial operation in Oklahoma, Tech's
3-dimensional lightning mapping system was set up in August of
1998 over a 60-km diameter area around Langmuir Laboratory and
the New Mexico Tech campus in central New Mexico. The results
show that lightning activity in New Mexico storms has a
simpler structure and smaller extent than in the larger Great
Plains storms. Lightning discharges are also much less
frequent in a storm, compared to the nearly continous activity
observed in Oklahoma. Intracloud lightning often has only a
vertical channel but in more developed storms shows a clear
bilevel structure, undoubtedly associated with the main
negative and upper positive charge regions of the storm.
These results agree with previous observations both in New
Mexico and in Florida.
A new finding is that cloud-to-ground discharges sometimes
show considerable activity in a third region below the
negative charge level, presumably associated with lower
positive charge. The overall lightning activity in the first
storm to be looked at (the storm of August 18) exhibited a
trilevel structure, consistent with the tripole model of storm
electrification, and appears to map out the basic charge
structure of the storm. Similar structures have been observed
in the more complex Oklahoma storms. A complete analysis of
the August 18 observations is expected to show the evolution
of the lightning activity throughout the life cycle of the
storm and will be compared to dual-polarization radar
observations of storm structure. The relation between the
lightning channel levels and the storm charge regions will be
investigated at Langmuir Laboratory in the summer of 1999
using balloon-borne electrostatic field measurements by
Marshall, Stolzenburg, and Rust.}
}
@ARTICLE{hayakawa_fagu98,
AUTHOR = {Masashi Hayakawa and Alexander P. Nickolaenko and
Irina G. Kudintseva and Stanislav V. Myand and
Leonid M. Rabinowicz},
TITLE = {Natural Sub-Ionospheric {ELF} pulses in Time Domain},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F143},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A31D-09 talk},
ABSTRACT = {There are problems when constructing the time domain
solution for the natural electromagnetic signals of the
extremely low frequency band. Such pulses originate from
the powerful lightning strokes and propagate in the
spherical Earth-ionosphere guide for long distances. Since
the wave attenuation in the lower part of ELF band is
small, the pulses multiply circle the Earth's circumference
giving rise to the Schumann resonance phenomenon. Recent
studies indicate on possible link between the red sprites
and the Q-burst pulses observed in the Schumann resonance
band (from a few to some tens Hertz frequencies) or with
the slow tail atmospherics. The standard way of obtaining
such a solution is following. The mode is used in the
frequency domain. The zonal harmonic series representation
is applied, which is an expansion of the fields over the
Legendre polynomials. Then, the fast Fourier transform is
applied to obtain the time domain solution. There are two
areas on the sphere where the solution in the frequency
domain becomes divergent. These are the vicinities of the
source and its antipode, where the radio wave focusing
occurs. To solve the problem everywhere in the spherical
Earth-ionosphere cavity, we construct the solution directly
in the time domain. For this purpose we make an analytical
Fourier transformation of each term in the zonal harmonic
series representation and then compute the time domain
fields by direct summing of the series obtained
analytically.
The main result of the report is following.
(i) One fails to describe the field at the point where the
source was regardless the time when computing the field in
the frequency domain first and then applying a FFT
algorithm. The time domain representation obtained allows
computing the electromagnetic pulse everywhere in the
Earth-ionosphere cavity for t > 0, including those
multiply crossed the Earth's circumference.}
}
@ARTICLE{sentman_fagu98_a,
AUTHOR = {D. D. Sentman},
TITLE = {The Effects of lightning on the middle and upper
atmospheres: Snapshot of a Rapidly Evolving Discipline},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F164},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-01 talk (invited)},
ABSTRACT = {Interest in the electrical effects of tropospheric
lightning on the middle and upper atmospheres took a sudden
leap in 1989 with the serendipitous video capture of a
cloud-to-stratosphere discharge by R. Franz and colleagues.
Shortly thereafter similar signatures were found by W. Boeck
and colleagues in space shuttle video tapes. Since these
seminal reports appeared, activity in this new field has
exploded as other researchers scrambled to determine the
nature and extent of this new phenomenon. Beginning in 1993
and continuing to the present, ground and aircraft based video
studies have amassed thousands of images of these middle
atmospheric apparitions, now generally referred to as
sprites, whose luminous flash within the mesosphere, at
altitudes of 50-90 km, coincides with a large underlying
positive cloud-to-ground lightning discharge. Spectral
measurements have identified the emitting atmospheric species
of red sprites (N2), and optical signatures of accompanying
ionospheric heating have been detected (ELVES). A new, even
more elusive and apparently unrelated electrical phenomenon
known as a blue jet was also discovered to spurt optically
upward directly from the top of a thunderstorm to altitudes of
about 40 km (130,000 ft). Measurements of electromagnetic
emissions have identified several distinctive signatures
associated with sprites: ULF impulses, Q-bursts in the ELF,
and slow tails in the VLF frequency bands. Ground-based VLF
studies have shown that a certain class of gamma ray bursts
observed from earth orbit originate in thunderstorms, and are
possibly part of the same process that produces sprites and
related phenomena. The focus of current ground and aircraft
experiments is to extend optical remote sensing into the
ultraviolet and infrared regimes as a way to determine the
energy budget of sprites/ELVES/jets, and to study their wide
band electromagnetic emission properties. Several satellite
initiatives are underway to perform topside studies of these
events unimpeded by the terrestrial atmosphere. This talk
will present an overview of past and present observations in
the rapidly evolving discipline of the effects of lightning on
the middle and upper atmospheres, and point out several areas
of possible significance of these processes in the larger
geophysical system.}
}
@ARTICLE{inan_fagu98,
AUTHOR = {Umran S. Inan and Christopher P. Barrington-Leigh
and Elizabeth A. Gerken and Timothy F. Bell},
TITLE = {Telescopic Imaging of Fine Structure in Sprites},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F164},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-02 talk},
ABSTRACT = {Recent theoretical work [{\it Pasko et al.}, {\it GRL,
25}, p. 2123, 1998] has indicated that the sprite optical
luminosity as observed in regular video may be constituted by
a superposition of a large number of highly structured
streamers having fine structure with scale sizes of few
meters. To look for the presence of such fine structure, we
use a 40-cm wide, $\sim$2-m tall Newtonian telescope with a
field-of-view of $0.92^\circ\times 0.7^\circ$ ($\sim$10-m
video resolution at a range of 500-km), boresighted with a
wide field-of-view ($12^\circ\times9^\circ$) video camera.
The rotatable and tiltable mounting base of the telescope
provides easy elevation and azimuth control, while aiming of
the telescope is facilitated by the known phenomenology of
sprites, i.e., that they often tend to occur at approximately
the same location for tens of minutes. Both the wide- and
narrow-fields-of-view are recorded with image intensified CCD
video cameras, with simultaneous recording of the broadband
very low frequency sferic signal from causative lightning
flashes. The first observations with the telescopic imaging
system were conducted from the Langmuir Laboratory annex,
located near the 11,000 ft high South Baldy peak, providing
clear views of thunderstorms in Kansas, Colorado, Texas, and
the north-west coast of Mexico. Preliminary data from the
telescope show the presence of a fascinating complex of fine
structures within the body of the sprite, clearly indicating
the presence of columnar channels of luminosity with lateral
extent $<$10-m. In one case, on July 13, 1998, observing a
storm ata range of $\sim$580 km, many tens of
multiply-oriented (but mostly vertical) streamer-like
structures were simultaneously observed within the field of
view, with lateral scales ranging from $<$10-m to up to
100-m.}
}
@ARTICLE{fukunishi_fagu98,
AUTHOR = {H. Fukunishi and Y. Takahashi and Y. Watanabe and
A. Uchida and M. Sato and W. A. Lyons},
TITLE = {Frequent Occurrences of Elves Discovered by Array
Photometer Observations},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F164},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-03 talk},
ABSTRACT = {Fukunishi et al.[1996] found that Elves occur just after
the onset of sferics but preceding to sprites. However, during
the SPRITES'98 campaign carried out at Yucca Ridge Field
Station, Colorado in July and August 1998, we discovered that
elves occur very frequently without sprites. For example, we
identified 52 elves events without sprites in 6 hours during
the night on August 1-2, 1998. Since the duration of elves is
about 1 ms, it is difficult to identify them on video images
except for unusually bright events. However, the
identification of occurrences of elves is easy by using array
photometer data since elves always show time delays with
decreasing elevation angles, but such time delays are not
observed for cloud flashes. We used two sets of 16-channel
array photometers set up in vertical and horizontal,
respectively. Each array photometer has individual
fields-of-view of 0.7 x 11 degrees and the total field-of view
of 11 x 11 degrees and the sampling time of each channel is 50
microseconds. Several important features were found. First,
elves are excited not only by positive cloud-to-ground
lightning discharges (CGs) but also by negative CGs. Second,
the durations of optical flashes measured by the vertical
array photometer are 200-500 microseconds for individual
channels and the onset of flashes delays with decreasing
elevation (time delay from top to bottom is 300-600
microseconds). Third, the durations of optical flashes
measured by the horizontal array photometer are 300-900
microseconds and the onset of optical flashes is simultaneous
with the almost same luminosity variations at all
channels. The observed features of elves are consistent with a
model proposed by Inan et al. [1996] in which the optical
emissions are produced as a result of heating by
electromagnetic pulses (EMPs) from lightning discharges. The
frequent occurrences of elves suggest that lightning-induced
EMPs are playing an important role for heating of the lower
ionosphere.}
}
@ARTICLE{barringtonleigh_fagu98,
AUTHOR = {Christopher P. Barrington-Leigh and Umran S. Inan
and Elizabeth A. Gerken},
TITLE = {Temporal and Spatial Structuve of Sprites and Elves:
Photometric and {CCD} Observations},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F164},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-04 talk},
ABSTRACT = {Data acquired with a high-speed photometric array (the
Fly's Eye) combined with high-resolution CCD imaging and Very
Low Frequency sferic recordings allow the precise measurement
of the onset delay, development, and duration of red sprites
and elves. The two complimentary optical instruments provide
the first simultaneous documentation of the spatial fine
structure and submillisecond temporal characteristics of
sprites and elves. Elves are unambiguously identified by
means of their rapid lateral expansion as observed with the
Fly's Eye and are clearly produced by both positive and
negative cloud-to-ground flashes. Bright sprites are found to
have typical durations of 30-100 ms, and the altitude
dependence of their observed structure and optical properties
is discussed. Elves and sprites are detected in both blue and
red photometers, and preliminary analysis indicates that the
ratio of blue and red emission intensities is consistent with
that expected for air breakdown at high altitudes.}
}
@ARTICLE{sentman_fagu98_b,
AUTHOR = {D. D. Sentman and E. M. Wescott and J. Winick and
C. Siefring and J. Morrill and D. Baker and P.
Bernhardt and M. Heavner and D. Moudry
and D. Osborne and J. Desrochers and L. Peticolas
and V. Besser},
TITLE = {The {EXL}98 Sprites Campaign},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F164},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-05 talk},
ABSTRACT = {The EXL98 (Energetics of Upper Atmospheric Excitation by
Lightning, 1998) project was a joint effort by the University
of Alaska, Air Force Research Laboratory, and Naval Research
Laboratory to study the energy budget of sprites, jets and
ELVES using jet aircraft and ground remote sensing methods.
The EXL98 field campaign was conducted from Colorado and
Wyoming during July, 1998, with aircraft flights targeted on
nocturnal thunderstorm systems in the Middle and Upper Plains
states. Simultaneous sprite observations were obtained from
the airborne imaging platform carrying a suite of eight low
light level television (LLTV) camera systems, and at two
ground locations equipped with LLTV, a spectrograph, and high
speed photometers. Campaign and flight mission planning were
carried out at the Laboratory for Atmospheric and Space
Physics (LASP) at the University of Colorado. The
measurements focused on low light level imaging across a wide
range of wavelengths, including the near ultraviolet (NUV),
visible, near infrared (NIR), and medium infrared (MIR). This
talk will review the science rationale for the EXL98 project,
discuss aircraft and ground resources utilized during the
campaign, and present preliminary results.}
}
@ARTICLE{bowles_fagu98,
AUTHOR = {Jeffrey H. Bowles and Carl L. Siefring and Jeff
S. Morrill and Paul A. Bernahrdt and Davis
D. Sentman and Dana R. Moudry and Eric J. Bucsela
and Daniel L. Osborne and Eugene M. Wescott and
Matthew J. Heavner},
TITLE = {Do Sprites Sometimes Connect to the Cloud Tops?},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F164},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-06 talk (withdrawn)},
ABSTRACT = {In this paper we present exciting results from the EXL98
mission which indicate that Sprites may occasionally connect
from the ionosphere all the way down to the cloud tops.
During the EXL98 mission one of the major goals was to obtain
Near-UltraViolet (NUV) and Near-InfraRed (NIR) measurements
of Sprites. Because of atmospheric absorption and
scattering, to fulfill these goals it was necessary to fly
the plane close to the storms (100-200km). As a result we
obtained many images which view from the horizon (cloud tops)
into the tendril portion of the Sprites. The NRL NUV camera,
running without a filter, observed two cases where it
appeared that a secondary breakdown started from near the
horizon and propagated upward toward the remnants of a
Sprite. The UAF narrow field visible camera was often
saturated by scattered light from the lightning flash in this
area. However, on a number of occasions this camera showed
'fingers' extending from the horizon to the bottom of the
Sprites as it came out of saturation. One of these cases
corresponds to the observations made with the NUV camera of a
possible secondary breakdown following the Sprite by several
video frames. The evidence for a 'direct' connection from a
Sprite to the cloud tops is not conclusive, but the
possibility is extremely important. We hope these results
will spur further experimental and theoretical investigations
into this possibility.
*The work at NRL was sponsored by NASA and ONR.
}
}
@ARTICLE{besser_fagu98,
AUTHOR = {Veronika Besser and Dana R. Moudry and Matt
J. Heavner and Davis D. Sentman and Eugene
M. Wescott and Jeff S. Morrill and Carl Siefring and
Daniel L. Osborne and Don L. Hampton},
TITLE = {Case Study of a Sprite},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F165},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-07 talk},
ABSTRACT = {On July 22, 1998, at 04:57:43 UT, a sprite over central Iowa
was imaged from the EXL98 aircraft from a very close range.
The sprite was captured in six cameras: a wide field (approx.
60$^\circ$ field of view (FOV)) monochrome camera, and five
narrow field cameras (approx. 16$^\circ$ FOV): a monochrome
camera, an intensified color camera, a camera filtered at
427.8 nm (FWHM 1.6 nm), a near-ultraviolet (340 nm) camera,
and a near-infrared (0.8-1.7 $\mu$m) camera. The entire
sprite was captured in the wide field camera, the other
cameras imaged only the tendrils.
\\In addition, approximately 100 ms after the onset of the
sprite, spike or finger-like features were seen propagating
upward from the cloudtops towards the lower portions of the
tendrils of the sprite, stopping short of reaching them.
This is the first time this feature has been reported.}
}
@ARTICLE{pasko_fagu98,
AUTHOR = {Victor P. Pasko },
TITLE = {Theoretical Models of Sprites},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F165},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-08 talk (invited)},
ABSTRACT = {Spectacular luminous optical emissions
appearing in clear air above thunderstorms and known as
sprites provide dramatic evidence of strong
electrodynamic coupling between tropospheric lightning
discharges and the mesosphere/lower ionosphere. In this
talk we will provide a review of existing interaction
and coupling mechanisms proposed for the explanation of
experimentally observed features of sprites (i.e.,
their spatial structure, optical spectra and time
dynamics). We will discuss the conventional as well as
the relativistic runaway breakdown processes stimulated
at mesospheric altitudes by large quasi-electroctatic
field transients following intense positive cloud to
ground lightning discharges, and the role of these two
breakdown mechanisms in sprite production. We will also
discuss the properties of sprites on a variety of
spatial scales, including their fine spatial structure
($\sim$1 m), as well as their contribution to the
large scale atmospheric electric circuit (scales
$>\sim$100 km). }
}
@ARTICLE{fernsler_fagu98,
AUTHOR = {Richard F. Fernsler and Harvey L. Rowland},
TITLE = {Theory and Experiment for Sprites and Elves},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F165},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-09 talk},
ABSTRACT = {Analytic models were previously given [1] for elves and
red sprites produced in the upper atmosphere, and recent
experiments provide support for the model predictions. The
underlying criterion is gas breakdown from the electric fields
induced by lightning discharges, and results were given for
both vertical and horizontal discharges. The radiation field
from a lightning return stroke was found to be capable of
producing flat, thin, short-lived elves just below the
ionosphere, provided the return-stroke current exceeds ~50
kA. Similarly, the quasi-static field from a continuing
current was found to be capable of producing red sprites
provided the charge moment (charge times height of charge)
exceeds ~150 Coulomb-km. In addition, red sprites are
predicted to elongate and filament as they propagate down in
altitude via enhancement of the field at the tip. Similar
enhancement does not occur for the radiation fields producing
elves. In this talk the two models are briefly reviewed and
then compared with experiment.
Work supported by NASA and ONR.
1. J. Geophys. Res. 101, 29653 (1996).}
}
@ARTICLE{armstrong_fagu98,
AUTHOR = {Russell A. Armstrong and David M. Suszcynsky and
Robert Strabley and Walter A. Lyons and Thomas
Nelson},
TITLE = {Simultaneous Multi-Color Photometric and Video
Recording of {S}PRITES and their parent lightning
mechanisms and energy deposition},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F165},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-10 talk},
ABSTRACT = {We have obtained new multi-color photometry data
simultaneously with blue, red and high-resolution broad-band
video imagery of sprite events which indicates that more than
one mechanism can cause sprites. The time-resolved emissions
from the nitrogen first-positive, second positive and first
negative systems indicate different time histories. We have
found that the relative time histories are not unique from
event-to-event but generally fall into two (or perhaps three)
categories. We find that the time histories can be
interpreted to yield both the ionization level and the energy
accommodation. Data has been obtained which confirms
ionization in sprites varying from very strongly ionized to
relatively weakly ionized. The simultaneous red and blue
video images associated with the sprite events indicates that
columnar sprites exhibit different energetic profiles than
carrots. We will present the systematic analysis of the
time-histories of the photometric emission behavior of the
sprite events, correlate them with the corresponding imagery
and discuss implications for the electrodynamic modeling of
the phenomena.}
}
@ARTICLE{taylor_fagu98,
AUTHOR = {Mike J. Taylor and Larry C. Gardner},
TITLE = {Simultaneous Red and Blue Imaging of Sprites During
the Yucca Ridge 1998 Campain},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F165},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-11 talk},
ABSTRACT = {As part of the Sprite-98 campaign conducted at Yucca
Ridge, CO two intensified Image Isocon cameras and a bare CCD
imager were used to investigate the spectral morphology of
Sprites. The CCD and one Isocon camera were filtered to
observe the nitrogen first positive band emission at 665 nm
while the second Isocon camera was used to detect any blue
emissions originating at ~400 nm. A fourth, Xyibon, camera
was unfiltered and used to provide reference image data. All
four cameras were co-aligned and mounted on a motorized
alt-azimuth tripod providing accurate pointing information.
Joint observations were conducted during a one month period
from 8 July to 5 August, and despite the limited storm
conditions Sprites were imaged successfully on several nights
in the red emission but only occasionally were they detected
simultaneously at blue wavelengths. An initial comparative
analysis of the red and blue Sprite signatures and their
associated lightning discharges will be presented together
with an unusual observation of light apparently propagating up
from an isolated Sprite and re-illuminating a meteor trail.}
}
@ARTICLE{heavner_fagu98,
AUTHOR = {M. J. Heavner and D. R. Moudry and D. D. Sentman and
E. M. Wescott and J. S. Morrill and C. Siefring and
E. J. Bucsela and D. L. Osborne and J. T. Desrochers
and H. Stenbaek-Nielsen and J. Winick and J. Kristl and
T. Hudson and L. M. Peticolas and V. Besser},
TITLE = {Ionization in Sprites},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F165},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-12 talk},
ABSTRACT = {The EXL98 sprite observing campaign of July 1998
involved multiple cameras across the wavelength range 300 nm
to 5 microns. A filter at 427.8 nm was used on one camera to
detect emissions from the first negative group of molecular
nitrogen, which would be a direct observation of the amount of
ionization. The filter was carefully selected to reject 426.8
nm light and any other second positive (non-ionized) molecular
nitrogen emissions which have made previous blue filtered
observations of sprites difficult to interpret with regards to
the ionization question. The paper will present observations
made with the filtered camera and simultaneous EXL98 aircraft
images as evidence for the observation of ionization. The
evidence for ionization will be discussed in the context of
previous observational campaigns.}
}
@ARTICLE{groves_fagu98,
AUTHOR = {Keith M. Groves and John M. Quinn and E. Russell
Shinn and Peter Ning and Matthew R. Cox},
TITLE = {An Upper Limit on Ionization in Sprites},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F165},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-13 talk},
ABSTRACT = {During the past few years, much progress has been made
towards characterizing the morphology of red sprites and
understanding the source mechanisms leading to their
occurrence. A combination of optical measurements and
theoretical calculations have been applied to determine the
levels of ionization produced in sprite discharges, but no
definitive results have yet been produced. During July-August
1996 we collected radio frequency (RF) measurements of
lightning-induced atmospheric effects in northeastern Colorado
using a 28 MHz coherent backscater radar. Such a radar serves
as a powerful diagnostic of electron density. A
CCD-intensified video system was co-located with the radar to
verify the occurrence of sprites within the radar beam. The
combined data sets were compared with CG lightning events as
recorded by the National Lightning Detection Network to
correlate RF signatures with individual lightning strikes.
More than 200 sprite events were seen simultaneously with the
radar and the optical system; numerous more events were
observed with the radar in the absence of good optical
conditions. No echoes associated with sprite occurrence were
observed. An analysis of the radar sensitivity and a
consideration of various scattering models enable one to place
an upper bound on the levels of ionization present in red
sprites. The resulting ionization values are strongly
dependent on the assumed structure and extent of the
scattering region. High resolution optical measurements and
theoretical analyses are needed to constrain the scattering
calculations further. Additionally, a number of uncorrelated
radar echoes were observed during the campaign, sometimes in
conjunction with thunderstorm activity. The significance of
these echoes and their origin will be discussed.}
}
@ARTICLE{swenson_fagu98,
AUTHOR = {Gary R. Swenson and Rick L. Rairden},
TITLE = {What is the source of the sprite seed electrons?},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F165},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A41C-14 talk},
ABSTRACT = {It is clear from spectral measurements of the N2 1PG
vibrational distribution originatin from Sprites,
that the energy distribution of
electrons responsible, had a mean of $~$1 eV. This energy is
orders of magnitude colder than auroral secondary electrons.
This cold source cannot be explained by normally produced
secondaries from electron induced ionization of local
molecules whose ionization thresholds are typically $>$15 eV.
A mesospheric source of low energy electrons can originate
from negative ions, where electron release energies are
typically .5-1.5 eV. It will be shown that measured
brightnesses of Sprite cores are consistent with
climatological average negative ion densities available.
The remaining question is to explain the souce of 'seed'
electrons, which when exposed to the broad electric field,
accelerate to remove the electrons from the parent molecules.}
}
@ARTICLE{green_fagu98,
AUTHOR = {Bryon David Green and Terry Rawlins and Russ Armstrong},
TITLE = {Molecular Excitation as a Probe of Sprite Mechanisms},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F175},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-01 talk (invited)},
ABSTRACT = {REGULAR MAIL}
}
@ARTICLE{winick_fagu98,
AUTHOR = {Jeremy R. Winick and Joseph A. Kristl and Thomas
Hudson and Davis D. Sentman and Eugene M. Wescott
and Laila Jeong and Carl Siefring and Daniel Osborne},
TITLE = {Do Sprites produce infrared emission? Preliminary
Results from {EXL}98},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F175},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-02 talk (withdrawn)},
ABSTRACT = {We present the preliminary results of measurements taken
by MWIR filtered video cameras from high altitude aircraft
flights during the EXL98 campaign. AFRL and USU Stewart
Radiance Laboratory provided video cameras filtered for the
2.8 $\mu{}m$ and 4.3 $\mu{}m$ bands. These bands are enhanced
in aurora as a result of emission from chemiluminscently
produced NO(v) ($\Delta{}$v=2 at 2.7-3.0 $\mu{}m$) and CO$_2$
($\Delta{}$v=1 at 4.3 $\mu{}m$) produced from near-resonanat
vibrational energy transfer from N$_2$(v). These processes are
initiated primarily by secondary electrons. In sprites we
anticipate most electrons are heated by discharge electric
field as opposed to being secondaries from ionization
processes. Observations of copious N$_2$ first positive
emission in sprites indicates that electrons of greater than 7
eV are present. Since the cross section for production of
N$_2$(v) is very large for electrons of 2-5 eV,enhancement of
CO$_2$ 4.3$\mu{}m$ is likely. Formation of NO(v$\geq{}2$)
depends upon higher energy electrons that dissociate and/or
ionize N$_2$, and its formation in sprites is less
certain. However, NO(v$\geq{}2$) emission is a useful
indicator of NO formation and can tell us whether sprites have
any photochemical impact in the region of the mesosphere where
the NO density is near its minimum.
In light of these observations we will examine the mplications
for IR radiance for space-based limb viewing geometry in which
case the background emission, atmospheric transmission, and
field-of-view limitations are less severe. We will also
discuss the similarities and differences between aurora
mechanisms and likely sprite mechanisms.}
}
@ARTICLE{bernhardt_fagu98,
AUTHOR = {Paul A. Bernhardt and Carl L. Siefring and Jeff
S. Morrill and Davis D. Sentman and Eugene
M. Wescott and Matthew J. Heavner and Daniel
L. Osborne and Eric J. Bucsela},
TITLE = {Near-InfraRed ({NIR}) Measurements During the
{EXL}98 Campaign},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F175},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-03 talk},
ABSTRACT = {A NIR digital/video camera operating in the spectral
range between 900 and 1700 nm was flown on the EXL98
missions. This camera had two functions. First, it was used
to monitor nighttime airglow which gives indications of
density structures in the neutral atmosphere. The camera
uses a relatively new technology Indium-Gallium Arsinide
(INGAAS) focal plane array which is sensitive in the NIR. It
offers many advantages over similar measurements in the
visible because of its sensitivity and the relative
brightness of the airglow in the NIR. In fact, from the
EXL98 airborne platform it was possible to monitor airglow
modulations at the full 30 frame/sec video rate. Second, was
to search for excitation of N2 first positive emissions in
the NIR by Sprites. The NIR experiment was extremely
successful -- observing both the first Sprite related NIR
emissions and the first correlation between structures in the
neutral density and visible and NIR Sprite emissions. In
addition, a number of cases were observed where features in
the background airglow appeared to be related to structures
in the thunderstorm clouds. In this paper we will present an
overview of these measurements.
*The work at NRL was sponsored by NASA and ONR.}
}
@ARTICLE{bucsela_fagu98,
AUTHOR = {E. J. Bucsela and J. S. Morrill and C. Siefring and
M. J. Heavner and D. R. Moudry and D. D. Sentman and
E. M. Wescott and D. L. Osborne and W. M. Benesch},
TITLE = {Estimating Electron Energies in Sprites from
1{NG}/2{PG} Intensity Ratios},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F175},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-04 talk},
ABSTRACT = {As part of the EXL 98 mission which observed sprites from an
aircraft, video images were taken with narrow passband
filters at 4278$\AA$ and 3407$\AA$ . These passbands
correspond to the N$_2$$^+$ 1NG (1,0) and N$_2$ 2PG (0,0)
bands, respectively. These filters were designed
specifically to have very narrow passbands in order to
exclude nearby contaminating emissions. This set of image
data will be used to generate intensity ratios of the above
spectral features, specifically 1NG(1,0)/2PG(0,0) which can,
in turn, be related to the population ratio of the
N$_2$$^+$(B) and N$_2$(C) states. By making assumptions
about the electron distribution we
can estimate the electron energies implied by the observed
intensity ratios. In this presentation, we will discuss the
details of both the method of estimating energies and the
observing techniques. Preliminary results from the EXL 98
mission will be discussed.}
}
@ARTICLE{takahashi_fagu98,
AUTHOR = {Yukihiro Takahashi and Yoshiaki Watanabe and Akihiro
Uchida and Masaaki Sera and Mitsuteru Sato and
Hiroshi Fukunishi},
TITLE = {Energy Distributions of Electrons Exciting Sprites
and Elves Inferred from the Fast Array Photometer
Observations},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F175},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-05 talk},
ABSTRACT = {Recent spectral observations and numerical model
calculations have suggested that the 1st and 2nd positive
bands of N$_2$ are dominant emissions in sprites and elves,
although it has been also reported that the sprite emission
contains the 1st negative band of nitrogen molecule ions
(N$_2$$^+$). The intensity ratio of 1st and 2nd positive bands
of N$_2$ gives information on the energy distribution of
electrons which excite nitrogen molecules through collision
processes. In order to investigate the spectral
characteristics of sprites and elves we employed two
multi-anode array photometers (MAPs) in the SPRITES '98
campaign. One of the MAPs with a shrap cut filter measures the
1st positive band in the range 560-850 nm, while the other
with a blue filter measures the 2nd positive band in the range
350-450 nm. Each photometer has 16 channels with individual
fields-of-view of 0.7\deg $\times$11\deg and samples data at a
rate of 20 kHz. During the campaign, we observed 22 sprites
and analyzed the ratio of 1st and 2nd positive bands in detail
for 7 events of them. It was found that the 2nd positive band
of N$_2$ was remarkably enhanced at the initial phase of
columnar sprites. We will discuss the temporal and spatial
changes of electron energy distributions quantitavely for both
sprites and elves based on these MAP data.}
}
@ARTICLE{bering_fagu98,
AUTHOR = {Edgar A. Bering and James R. Benbrook and Eugene
M. Wescott and Davis D. Sentman and Hans
C. Stenbaek-Nielsen and Walt A. Lyons},
TITLE = {The {SPRITES} 99 Balloon Campaign},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F176},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-06 talk},
ABSTRACT = {There are several competing models for the production of
sprites, jets and elves. It has become clear it is not
possible to select between these models using only
ground-based data, owing to the fact that the ground shorts
out the field signatures of interest. Consequently, a balloon
campaign was proposed and funded. The campaign, which was
originally scheduled for July, 1998, has been rescheduled for
July and August of 1999. The 1999 Sprite Balloon Campaign
will attempt to conduct six high altitude balloon flights
from Ottumwa, Iowa, during the dark of the moon in the summer
of 1999. Nominal campaign dates include July 6-21, and August
4-19, with lower priority fall-backs of June 7-21 and
Sept. 3-17. The balloons will be launched at sunset, float at
a nominally constant altitude of 32 km and drift westward at
a predicted speed of 40 knots. Cutdown will occur after
sunrise in central Colorado. Balloon tracking will be made
available in real-time on redundant Web sites. The balloon
payloads will be instrumented with dual three axis electric
field detectors, three axis fluxgate and induction
magnetometers, X-ray scintillation counter, Geiger-Mueller
tube, upward looking high-speed photometer, vertical current
density ammeter, conductivity measurements, and an ambient
temperature thermometer. A multiply redundant telemetry
scheme will give us five orders of magnitude of dynamic range
in field amplitude sensitivity. The use of event triggered
on-board memory will allow us to sample 8 quantities at a
digitization rate of at least 50 kHz per channel during
sprite events. The efficiency of the on-board event trigger
will be checked by using 4 broad-band analog waveform
channels. Ground observations may include low light level TV
observations from as many as three sites: tentatively, WIRO,
on Jelm Mtn., Wyoming, Mt Evans, Colorado, and Yucca Ridge,
Colorado. At least one of these sites will also have a fast
photometer. Other topics that will be covered include: why
the program was postponed and the trigger criteria for the
on-board fast memory.}
}
@ARTICLE{chern_fagu98,
AUTHOR = {Jyh-Long Chern and Lou-Chuang Lee and Kuan-Ren Chen
and Rue-Ron Hsu and Han-Taong Su and Chin-Chun Tsai},
TITLE = {{ISUAL} Project: Observations of Red Sprites on
{T}aiwan's {ROCSAT}-2},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F176},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-07 talk},
ABSTRACT = {A satellite observation mission of red sprites has been
planned on ROCSAT-2, which is to be launched in June 2002.
ROCSAT-2, the second scientific satellite of Taiwan, is
a low-earth orbit sun-synchronous satellite, with an
altitude 891km and inclination angle 98.9$\deg$.
The scientific payload, ISUAL (Image of Sprite; Upper
Atmospheric Lightning), will contain a two-dimensional
CCD imager, 6 narrow-band photometers, and 2 photometer
arrays. The ISUAL imager is a limb viewing instrument
pointing in a side direction, which is perpendicular to
the satellite moving direction and away from the sun.
The main objectives are (1) to obtain the global
distribution of red sprites, (2) to determine the
spatio-temporal dynamics of red sprites, (3) to identify
the UV bands, (4) the degree of ionization in the sprite
emission region; (5) to observe airglows and auroras.
International collaborations have been established and will
be further encouraged.}
}
@ARTICLE{marshall_fagu98,
AUTHOR = {Lee H. Marshall},
TITLE = {An Overview of Electromagnetic Measurements Relating
to Sprites, Elves and Jets},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F176},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-08 talk},
ABSTRACT = {During the past several years, numerous measurements
have been made of lightning- related middle and upper
atmosphere (30-100km) optical phenomenon such as sprites,
elves, and jets. The relationship of these events to parent
lightning strokes and storms suggests energy coupling
processes upward from the lower atmosphere. The large
geometry and time-scale of sprites and particularly jets, and
comparatively short time-scale of elves suggest energy
coupling processes that could be quite different from each
other and whose duration may vary over several orders of
magnitude. For these reasons, electromagnetic measurements
have been made, in conjunction with optical observations,
extending from the sub-hertz ULF range, through the widely
studied ELF and VLF ranges, the LF and HF ranges and up into
the VHF and UHF ranges. This paper will present an overview
of the electromagnetic measurements relating to sprites,
elves, and jets. Both electric and magnetic field
measurements over a wide range of frequencies and distances
will be discussed. Also, apparent differences between the
theoretical explanations and the empirical observations will
be discussed, and the areas greatly in need of additional
observation will be outlined. }
}
@ARTICLE{bell_fagu98,
AUTHOR = {Timothy F. Bell and Chris Barrington-Leigh and
Elizabeth A. Gerken and Umran S. Inan},
TITLE = {Continuing Currents, Charge Transfer, and Optical
Emissions Associated with Red Sprites Observed in
Thunderstorms in {M}exico},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F176},
MONTH = {November},
ANNOTE = {Fall AGU 1998, A42D-09 talk},
ABSTRACT = {Red Sprites consist of large scale, transient, luminous
, predominently red structures in the mesosphere which appear
above thunderclouds following positive cloud-to-ground
lightning discharges. Over the past few years Sprites have
been extensively studied and documented in the midwestern US,
where they are very common during the summer months. Although
it is well known that Sprites occur in storms at other
locations, such as Florida, Australia, the Amazon basin, and
Africa, much less is known of the characteristics of these
Sprites. During the summer of 1998, Stanford University
operated a number of instruments at the Langmuir Laboratory in
New Mexico in order to observe Sprites that occurred within ~
900 km of the laboratory. On a number of evenings vigorous
Sprite activity was observed in thunderstorms in northern
Mexico. In the present paper we present optical images of the
Mexican Sprites in conjuction with calculations of the
continuing current and positive charge transfer associated
with each Sprite, and discuss the differences between Sprites
in the midwestern US and northern Mexico.}
}
@ARTICLE{wescott_fagu98,
AUTHOR = {E. M. Wescott and D. D. Sentman and
H. C. Senback-Nielsen and M. J. Heavner and
D. R. Moudry and U. S. Inan and T. F. Bell and
M. Stanley},
TITLE = {`Columniform' Sprites: Their Optical
Characteristics, {ELF} and {VLF} Signatures, and
Relationship to Lightning},
JOURNAL = {EOS Supplement},
YEAR = 1998,
VOLUME = 79,
NUMBER = 45,
PAGES = {F176},
MONTH = {November},
ANNOTE = {FAll AGU 1998, A42D-10 talk (withdrawn?)},
ABSTRACT = {This paper summarizes observations since 1995 of a
distinctive form of sprites associated with positive CG
flashes in mesoscale thunderstorms, and discusses physical
mechanisms for their features. We have examined the
relationships between the visible forms, the causative
lightn