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2.7 A REVIEW OF ELECTRICAL AND TURBULENCE EFFECTS OF CONVECTIVE STORMS ON THE OVERLYING STRATOSPHERE AND MESOSPHERE

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2.7 A REVIEW OF ELECTRICAL AND TURBULENCE EFFECTS OF CONVECTIVE STORMS ON THE OVERLYING STRATOSPHERE AND MESOSPHERE

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The electrical and turbulence effects on convective storms on the overlying stratosphere and mesosphere are discussed. Intense electric fields and a suite of upward propagating, lightning-like discharges and blue-jet like phenomena are a common, albeit transient, part of the environment. The role of thunderstorms in generating hydrodynamical instabilities, shear and significant vertical motions extending many kilometres above visible storm tops is beginning to be appreciated. It is suggested that those planning to operate high altitude airship (HAA) within the region should be aware that what has been heretofore presumed about the weather of this region may not be necessarily always true.
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2.7 A REVIEW OF ELECTRICAL AND TURBULENCE EFFECTS OF CONVECTIVE
STORMS ON THE OVERLYING STRATOSPHERE AND MESOSPHERE
Walter A. Lyons*
FMA Research, Inc., Fort Collins, Colorado
Russell A. Armstrong
Mission Research Corporation, Nashua, New Hampshire
1. INTRODUCTION
According to The National Space Weather Program
(NSWP), “space weather” refers to conditions on the Sun
and in the solar wind, magnetosphere, ionosphere and
thermosphere that can influence the performance and
reliability of space-born and ground based technological
systems and can endanger human life or health (OFCM,
1997). Well documented have been the impacts of
energetic particles and geomagnetic storms on satellite
and communication systems, induced currents in the
electric power systems due to geomagnetic field
fluctuations, and space weather hazards to astronauts.
The NSWP Implementation Plan notes that the goals of
the National Space Weather Program can be achieved
only when the representation of space weather is
coupled into a seamless system, starting at the sun and
ending at the Earth. One can not dispute this notion, but
this paper suggests that a slightly broader perspective
might be in order. We note that an indirect solar
influence upon the middle atmosphere derived from
heating of the surface deserves growing attention.
Insolation warms the Earth’s surface which in turn
generates deep convection, further resulting in significant
hydrodynamic and electrodynamic disturbances
throughout much of the middle atmosphere. The impacts
of tropospheric thunderstorms are now understood to
extend through the depth of the stratosphere,
mesosphere and even into the lower ionosphere. This
region sometimes, only partly in jest, is termed the
“ignorosphere,” because its presumed quiescence and
inaccessibility has lead to a dearth of remote and in situ
measurements. Satellites and Space Shuttles overfly this
region. Sounding rockets can only obtain readings lasting
mere seconds. Costs and performance limitations limit
aircraft and balloons to brief probes of the very lowest
extremity of the region. Yet the thin atmosphere beyond
the tropopause is soon to become increasingly
populated. Proposed high altitude airships (HAAs),
including station-keeping balloons and UAVs, may be
deployed for various purposes including research,
communications and national security surveillance.
Upcoming generations of civil transports and military
aircraft will log increasing time in the atmosphere above
thunderstorms. The Space Shuttle
____________________________________________
Corresponding Author: Walter A. Lyons, CCM
FMA Research, Inc., Fort Collins, CO 80524,
walyons@frii.com, www.FMA-Research.com
and its successors must continue to ascend and descend
through the region. The speculation (in part fueled by the
press) about the possibility that the Shuttle Columbia was
felled by interaction with a sprite, and the considerable
effort needed to discount this as a plausible cause
(NASA JSC 2003), highlighted the limitations in our
understanding of the electrodynamics of the region
between 20 and 90 km. This paper surveys recent
research which suggests that the stratosphere, as well as
the overlying mesosphere, are neither electrically nor
dynamically “uninteresting.” Those planning to operate
HAAs within the region should be aware that what has
been heretofore presumed about the “weather” of this
region may not be necessarily always be true.
2. A CAUTIONARY TALE
During the summer of 1999, the authors were
preparing to participate in a major NASA scientific
balloon mission to study sprites above High Plains
thunderstorms (Bering et al. 2002). Sprites are the most
common middle atmospheric transient luminous event
(TLEs) induced by intense electrical activity in deep
tropospheric convective storms (Fig. 1). Lasting for a few
to tens of milliseconds, they illuminate thousands of cubic
kilometers of the atmosphere between 30 and 90 km
(Lyons et al. 2000), in a fleeting thunderstorm-induced
“aurora.” It is increasingly agreed that sprites result from
conventional electrostatic breakdown at around 70 km,
the result of intense electrical fields caused by the
removal of large amounts of electrical change from
clouds by unusual cloud-to-ground (CG) lightning
strokes. Electrical streamers extend both upward and
downward, but are generally not thought to contact the
underlying cloud tops. During the final planning stages for
the 1999 balloon missions, NASA informed the
participants that the balloons would not be allowed to
directly overfly thunderstorms. This was the result of
regulations imposed after a little-known 1989 balloon
mishap, which was ranked as the second worst “federal
disaster” of that year, behind the crash of an F-15.
On the morning of 6 June 1989, NASA launched a
nearly 30 million cubic foot research balloon from its base
in Palestine, TX. It carried a two-ton science payload (a
laser system for chemical measurements). The balloon,
as expected, reached a flight altitude of 120,000 ft (~37
km) and drifted westward. As evening approached it
began to overfly a large region of severe thunderstorms
in west Texas. The balloon then gradually descended to
110,000 ft (33.5 km) by 0038 UT 7 June 1989, about 55
miles (88km) west of Ft. Worth, TX. At that point an
uncommanded payload release occurred. The balloon,
parachute assembly, and payload descended, landing in
three different areas. The 4000 lb science payload, some
6 feet in diameter and 5 feet tall, struck the ground near
Graham, TX at an estimated speed of 600 mph, burying
itself in a small crater. Fortunately there were no injuries
or collateral property damage. Flight 1482P was declared
a failure, with a loss of $1 million in equipment and
payload.
What caused the uncommanded payload release has
been a matter of considerable conjecture and concern
ever since. Two PC cards from the flight termination
electronics page were retrieved, inspected, and found to
have suffered electrical damage and overheating. The
command strobing chip was damaged and discolored
due to electrical overstress and heating. Several pins
were found shorted together with evidence of arc-over.
The investigating committee determined the most
likely cause was “low-level high-voltage current induced
into the termination electronics package by lightning
activity present in the area.” However, it seems
improbable that activity within the storms below could
explain this incident. At the time of the failure, the balloon
was approaching thunderstorms with reported radar echo
tops to 65,000 ft (19.8 km). Even if directly above the
highest part of the storm, the balloon was fully 14 km
distant from any conventional lightning discharge within
the storm.
The event occurred almost exactly a month before
the first sprite was imaged by a low level camera above a
storm system in Minnesota (Franz et al, 1990), an event
which has changed our perception of electrical
phenomena in the middle atmosphere above storms.
Discoveries since that time may shed new light on the
fate of Flight 1482P.
3. A CONNECTION TO THE IONOSPHERE
Since 1989, more than 10,000 low light television
(LLTV) images of sprites have been obtained by various
research teams (Lyons, 1996; Sentman et al. 1995;
Lyons et al., 2000, 2003a). Blue jets (Wescott et al, 1995)
and elves (Fukunishi et al. 1995) have also been
observed with a variety of sensors. While a sprite is
unlikely to have directly interacted with the balloon, the
application of theories proposing conventional dielectric
breakdown as the initiator of sprites suggests electrical
transients on the order of 103 to 104 V/m may have
occurred at flight level (Williams, 2001; Rowland, 1999).
Such transients result from rather rare and unusually
powerful lightning discharges lowering hundreds of
Coulombs of charge to ground, as detailed by Hu et al.
(2002), Lyons et al. (2003a) and others. Systems not
deigned with the potential for such transients in mind may
indeed be expected to encounter failure modes. And in
the decade since the discovery of sprites, many other
TLEs, many emanating directly from cloud tops, have
been discovered. It is certainly not out of the question
that the NASA balloon passed far closer than 14 km to an
electrical discharge, or possibly was even directly
involved in such an event.
Many anecdotal reports in the literature events
(Vaughan and Vonnegut, 1989; Lyons and Williams,
1993; Heavner, 2000; Lyons et al. 2003b) described
TLEs which can not be categorized as sprites:
“…vertical lightning bolts were extending from the tops of
the clouds…to an altitude of approximately 120,000
feet…they were generally straight compared to most
lightning bolts…”
“…at least ten bolts of lightning went up a vertical blue
shaft of light that would form an instant before the
lightning bolt emerged…”
“...a beam, purple in color…then a normal lightning flash
extended upwards at this point…after which the
discharge assumed a shape similar to roots in a tree in
an inverted position…”
“…an ionized glow around an arrow-straight finger
core…”
“…an American Airlines captain…near Costa Rica…saw
from an anvil of a thunderstorm….several discharges
vertically to very high altitudes…the event was white…”
“…the top of the storm was not flat…looked like a dome
of a van de Graff generator...clearly saw several bolts of
lightning going upwards…dissipating in the clear air
above the storm…all in all 5 or 6 occurrences …”
Upward extending white channels topped by blue
flame-like features were captured on film near Darwin,
Australia (Lyons et al. 2003) and over the Indian Ocean
(Wescott et al. 2001). This latter event reached a height
of ~35 km. Welsh geographer Tudor Williams, who in
1968 was residing near Mt. Ida, Queensland, Australia,
visually observed a series of lightning-like channels rising
at least several kilometers above the top of a large
nocturnal thunderstorm. He photographed several of the
approximately 15 events (using 50 ASA 35 mm
transparency film, long exposures) that occurred at fairly
regular intervals over a 45 minute period. Figure X shows
the bright upward channel along with a hint of a faint blue
flame flaring upward and outward from its upper portion
reaching a height equal to or greater than the bright
channel. Upward-extending electrical discharges from a
supercellular thunderstorm over Colorado were observed
during the Severe Thunderstorm Electrification and
Precipitation Study (STEPS) on 22 July 2000 (Lyons et
al., 2003b).
Eyewitness recollections of many lightning-like
channels emanating from overshooting convective
domes of very active storm cells have a number of
common characteristics. They appear bright white to
yellow in color, are relatively straight, do not flicker,
extend above cloud tops to heights equal to or exceeding
the depth of the cloud (10-15 km), are notably long
lasting (~1 second) and can be observed during daylight.
It is difficult to understand how these might represent the
faint blue jet phenomenon reported by Wescott et al.,
(1995).
On 15 September 2001, a team of scientists familiar
with sprites and blue jets were investigating the effects of
lightning on the ionosphere at the Aricebo Observatory in
Puerto Rico (Pasko et al., 2002). At 0325.00.872 UTC,
above a relatively small (~2500 km2) storm cell 200 km
northwest of Arecibo, the LLTV video captured an
amazing upward discharge, blue in color, one frame of
which is shown in Figure 1 (see the full animation at
http://pasko.ee.psu.edu/Nature). Clearly seen as brilliant
blue to the naked eye, it appeared as a series of upward
and outward expanding streamers which rose from the
storm top (16 km). The event reached a terminal altitude
of 70 km, the estimated lower ledge of the ionosphere.
The event lasted almost 800 ms, including several re-
brightenings. This case marks the first hard evidence of a
direct electrical link between a tropospheric thunderstorm
cell and the ionosphere. A series of five similar giant
upward jets have since been reported emanating from
thunderstorm tops over the Pacific near the Philippines
(Su et al. 2003). While sprites are believed to occur with
a global frequency of several per minute, the number of
upward jets and lightning-like discharges remains
unknown. It is becoming clear, however, that they are
less rare than once believed.
A wide variety of upward electrical discharge
phenomena occur from thunderstorm tops, many
penetrating the stratosphere and some extending through
the mesosphere. As scientific and defense platforms
expand their domain into the stratosphere, it is
imperative that the dynamic electrical nature of the region
be considered. Sprites, jets and related TLEs are also a
potential source “optical clutter” for spaceborne
monitoring and missile detection systems. To the extent
their optical signatures are not well characterized, the
potential remains for natural phenomena to be
misidentified.
4. VERTICAL MOTIONS AND TURBULENCE
It has now become recognized that large thunderstorm
systems can generate upward propagating gravity waves
which often amplify with height, perhaps even breaking in
the middle atmosphere (Taylor and Hapgood 1990;
Alexander et al. 1995). The large mesoscale convective
systems of the High Plains, often prolific sprite producers,
have been known to generate gravity wave trains visible
from OH airglow emissions at the ~85 km level (Sentman
et al. 2002). These waves are often bright enough to be
visible with the naked eye.
Yet this energy must first propagate through the
stratosphere, a thermally stable layer often characterized
as devoid of “weather.” The very stability which makes
this characterizations true on a global scale also can
result in significant turbulence, vertical motions and wind
shears on the scale of convective storms. Evidence is
accumulating which suggests these storm’s impacts may
extend for ten km, and maybe much more, above cloud
tops. As contemporary aircraft routinely fly around and
not over thunderstorms, little operational experience is
available documenting conditions above intense
convective storms. Occasional ER-2 missions above
deep convective storms have tended to concentrate on
optical and electrical field measurements. Similarly, high
altitude research balloon missions are not instrumented
to determine convective scale turbulence, vertical motion
and wind shears. Learjet flights investigating tornadic
storms by the late Prof. T. T, Fujita nearly three decades
ago, used photogrammetric methods to reveal the
extreme turbulence and wind shear present at the top
and above intense convective storms (Fujita, 1992).
Figure 3 shows a montage of phenomena present above
thunderstorm tops. The tropopause is not necessarily a
boundary for “weather” or even mass flux. We note Wang
(2002) has demonstrated that flow around and over deep
convection generates intense gravity wave motions which
can transport material from the storm into the
stratosphere itself. Included in Figure 3 is a scene from a
video which reveals a stratospheric cirrus plume several
kilometers above the top of a supercell storm observed
during the 2000 STEPS program. Animation makes it
clear that this plume was formed by intense gravity wave
action extending well above the storm top. Such intense
motions above storms have also been indicated by high
resolution numerical simulations of airflow around and
over convective domes penetrating into the stratosphere
(Droegemeier et al. 1997). As shown in Figure 4, such
motions can reach several meters per sec many
kilometers above the visible storm tops. Such
“tropospheric style” conditions could well pose control
issues for station keeping HAAs or UAVs operating in the
lower stratosphere unless accounted for in the design of
these platforms.
5. SUMMARY
Research over the past decade has drawn attention
to the fact that the middle atmosphere is not devoid of
“weather.” Intense electric fields and a suite of upward
propagating, lightning-like discharges and blue-jet like
phenomena are a common, albeit transient, part of the
environment. Similarly, the role of thunderstorms in
generating hydrodynamical instabilities, shears and
significant vertical motions extending many kilometers
above visible storm tops is beginning to be appreciated.
Those planning to fly a variety of next-generation
vehicles in the lower layers of the “ignorosphere” should
not assume that this layer is quiescent. While perhaps
more properly referred to as “edge of space weather,” a
better understanding of these phenomena is required for
a wide range of disciplines besides aviation operations,
including studies of the global electrical circuit (Rycroft et
al. 2000), middle atmospheric NOx chemistry, aircraft
safety (Uman and Rakov 2003), infrasound research
(Bedard and Georges 2000) and RF propagation (Rodger
1999).
ACKNOWLEDGEMENTS. This material is based in part
was upon work supported by the National Science
Foundation, under Grant No. ATM-0221512 to FMA
Research, Inc. Special thanks to Victor Pasko, Eugene
Wescott, Patrice Huet, Mark Stanley, O.H. Vaughan,
Dave Sentman and Tudor Williams for supplying their
photographs. We wish to thank Dwight Bawcom, NASA
(retired) for providing information related to Flight 1482P.
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Figure 1. A montage of transient luminous events observed above thunderstorm systems from the ground, aircraft
and the Space Shuttle (top). Figure 2. Photograph of an “upward lightning bolt” which penetrated into the
stratosphere above an Australian thunderstorm system, while persisting for up to 2 seconds (bottom).
Figure 3. Evidence of the turbulent state of the atmosphere in the stratosphere above deep convective storms.
Figure 4. Numerical simulation of the vertical motions (lower panels) induced by an intense thunderstorm in
the clear air above storm tops (Droegemeier et al. 1997). Values of several meters per second occur. The top of
the modeling domain in this example was set at 20 km. We would expect that if the modeling domain were
extended upward to 30 km or higher, the impact of the storm would still be significant at those altitudes.
... The unanticipated discovery of red sprites in 1989 changed forever our view of the interactions between tropospheric electrical activity and middle atmospheric optical phenomena (Franz et al. 1990; Lyons and Armstrong 2004). Once thought to be electrically quiescent, the stratosphere and mesosphere are increasingly found to be the home to a growing variety of lightning-related electrical discharges and intense transient electric fields (Lyons 2006). ...
... During STEPS, the Duke ELF system obtained the ∆Mq values for a large number SP+CGs. For those events with moderately long CG-to-sprite onset time delays of ~6-10 ms, little correlation between peak current and ∆Mq could be found (Lyons et al 2004). This is consistent with the notion that for sprites with time delays greater than several milliseconds after the SP+CG much of the charge transfer occurs after the initial return stroke (as measured by the NLDN), and is accomplished by continuing currents of considerable magnitude (likely fed by the extensive dendrite patterns of spider lightning spreading outward into the large laminae of positive charge found in the MCS stratiform region). ...
... The serendipitous discovery of red sprites in 1989 changed forever our view of the interactions between tropospheric electrical activity and middle atmospheric optical phenomena and energetics (Franz, 1990;Lyons and Armstrong, 2004). Once thought to be electrically quiescent, the stratosphere and mesosphere are increasingly found to be the home to a growing variety of lightning-related electrical discharges and intense transient electric fields (Lyons, 2006;Lyons et al., 2003a). ...
Chapter
Full-text available
Emerging real-time capabilities using sensitive ULF/ELF/VLF magnetic receivers can monitor the impulse charge moment changes (iΔMq) of cloud-to-ground lightning strokes (CGs) over large regions. This provides a means to detect the parent CGs of the most common of the transient luminous events (TLEs) – sprites (often preceded by halos.) As iΔMq values grow larger than 100 C km, +CGs have a rapidly increasing probability of producing mesospheric sprites. If the iΔMq value of a +CG is >300 C km, there is a >75–80% chance this CG stroke initiates a sprite. Curiously, while negative iΔMq values of this size are much less common, they do occur. Yet on only a rare occasions have –CGs been documented to initiate a sprite over continental stroms (the so-called polarity paradox). The total charge moment change required to initiate sprites is believed to be at least ∼500 C km. Also, the great majority of sprite initiations are delayed after the return stroke by much more than the 2 ms time period used in the iΔMq estimates. This suggests that while both positive and negative CGs may have relatively large iΔMq values, due to the relatively low amperage continuing currents in the negative discharges, only +CGs have large enough continuing currents to routinely reach breakdown values and initiate sprites. While both CG polarities can theoretically initiate sprites, perhaps a somewhat higher breakdown threshold may exist for –CGs, and/or reduced streamer development makes them more difficult to detect optically? Preliminary climatologies of iΔMq for the U.S. are presented. The technique employed in the U.S. utilizes the National Lightning Detection Network for geolocation, allowing placement of >80–90% of sprite parent +CGs. Global lightning location systems such as the Worldwide Lightning Location Network (WWLLN) appear to detect approximately 25% of the CGs producing U.S. sprites, suggesting the possibility of employing such systems elsewhere.
... The serendipitous discovery of red sprites in 1989 changed forever our view of the interactions between tropospheric electrical activity and middle atmospheric optical phenomena and energetics (Franz et al. 1990;Lyons and Armstrong 2004). Once thought to be electrically quiescent, the stratosphere and mesosphere are increasingly found to be home to a growing variety of lightningrelated electrical discharges and intense transient electric fields (Lyons 2006;Lyons et al. 2003a). ...
... The analysis of the RHESSI spectra suggests that the source is in the range 15-21 km implying that thunderstorms and not sprites may be at the origin of TGFs (Dwyer and Smith, 2005). Upward lightning events indicate active processes at the top of thunderstorm clouds (Lyons and Armstrong, 2004). ...
Article
TARANIS (Tool for the Analysis of RAdiations from lightNIngs and Sprites) is a microsatellite project of the CNES Myriade program, dedicated to the study of impulsive transfers of energy between the neutral atmosphere the ionospheric and magnetospheric plasmas. The science objectives include: (a) characterization of TLEs (Transient Luminous Events) and TGFs (Terrestrial Gamma-ray Flashes) including their global mapping, occurrence rates and the correspondence between both phenomena in order to determine the source mechanisms, (b) determination of triggering factors and formation conditions, (c) characterization of the parent lightning that causes TLEs and TGFs, (d) investigation of wave-particle interactions leading to precipitated (LEP) and accelerated (runaway) electrons, (e) effects on the radiation belts of low altitude sources by tracking of their variability from electron and wave measurements, (f) effects on thermospheric parameters (ionisation rate, NOx, O3, dynamics of the atmosphere) by on board measurements coordinated with ground-based observations. The project is multidisciplinary and uses complementary instrumentation including: micro cameras and photometers, X and gamma detectors, high energetic electrons spectrometers, electric and magnetic sensors.
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The development of the Infrasound International Monitoring System, used for the verification of the Comprehensive nuclear Test Ban Treaty, represents a powerful tool to measure permanently, at a global scale and over large periods of time, the characteristics of the waves and dynamics of the atmosphere in relation with the climate. The first way is to monitor quasi-continuous infrasound sources such as ocean swells or volcanic eruptions to determine the fluctuations of the stratosphere and mesosphere in relation to the activity of planetary waves and large scale polar disturbances such as Vortex Intensification or Sudden Stratospheric Warming. The second way is to monitor gravity waves which are observed in the lower frequency range of the infrasound data. Large scale waves, mainly produced in tropical regions, influence the mean circulation of the middle atmosphere by transporting moment and energy from tropical to polar regions with a possible role on tropospheric climate. This paper demonstrates through different examples the potential of the network to observe these waves as well as changes in the atmospheric wave guide in relation to atmospheric parameters. As the network will provide long duration observations, it is suggested to use them to study the atmosphere in relation with the climate evolution.
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This contribution reviews the basics of atmospheric deep convection and electri- fication as it pertains to the generation of stratospheric and mesospheric transient luminous events (TLEs). Emphasis is placed on sprites and sprite-producing lightning, and the meteorological regimes in which they are found.
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Sustained heating of lower ionospheric electrons by thundercloud fields, as recently suggested by Inan et al. [1996], may lead to the production of enhanced infrared (IR) emissions, in particular 4.3-mum CO2 emission. The excitation rate for N2(v) via electron collisions is calculated using a new steady-state two-dimensional electrostatic-heating (ESH) model of the upward coupling of the thundercloud (TC) electric fields. The vibrational energy transfer to CO2 and 4.3-mum radiative transfer are then computed using a line-by-line non-LTE (non-local thermodynamic equilibrium) radiation model. Limb-viewing radiance profiles at 4.3-mum and typical radiance spectra are estimated for five different TC charge distributions and ambient ionic conductivities. Broadband 4.3-mum enhancements of greater than a factor of two above ambient nighttime levels are predicted for tangent heights (TH) in the range ~80 to >130km for the most perturbed case, with larger enhancements in selected narrower spectral regions. The predicted IR enhancements should be observable to an orbiting IR sensor.
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We show that electric field discontinuities occur above the stratiform clouds associated with mesoscale convective systems. Above cloud top, 12 discontinuities were observed at altitudes between 10 and 16 km. The field changes of the discontinuities ranged from -1.1 to -4.0 kVm-1. The data suggest that the electric field discontinuities were caused by coincident, positive, cloud-to-ground lightning flashes. The coincident ground flashes included both single and multiple return stroke flashes, with first-stroke peak currents between 20 and 154 kA. We modeled the electric field change that would occur if lightning discharged a horizontally extensive positive charge layer within the stratiform cloud. In the model, disks with charge densities of 1 and 3 nCm-3, a thickness of 400 m, and diameters ranging from 20 to 200 km were discharged and produced field changes similar to the observed above-cloud field discontinuities. Our results support the idea that sprites may be initiated by above-cloud field changes caused by positive cloud-to-ground lightning flashes that discharge a horizontally extensive charge region in the stratiform cloud of a mesoscale convective system. During the time between the electric field discontinuities the electric field above the stratiform clouds was -0.5 to -1.0 kVm-1 this field may be important in the global electrical circuit because the stratiform clouds have large horizontal extents (~104 km2).
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Water vapor in the lower stratosphere may play significant roles in the atmospheric radiative budget and atmospheric chemistry; hence it is important to understand its transport process. The possibility of water vapor transport from the troposphere to the stratosphere by deep convection is investigated using three-dimensional, nonhydrostatic, quasi-compressible simulations of a Midwest severe thunderstorm. The results show that the breaking of gravity waves at the cloud top can cause cloud water vapor to be injected into the stratosphere in the form of plumes above a thunderstorm anvil. Meteorological satellites and aircrafts have observed such plumes previously, but the source of water vapor and the injection mechanism were not identified. The present results reveal that there are two types of plumes, anvil sheet plumes and overshooting plumes, in this injection process and that the process is diabatic. A first-order estimate of this plume transport of water vapor per day from the upper troposphere to the lower stratosphere was made assuming that all thunderstorms behave the same as the one simulated. Other trace chemicals may also be similarly transported by the same mechanism.
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Transient luminous events (sprites, blue jets, elves) above large mesoscale convective systems (MCSs) over the U.S. High Plains have been routinely monitored from the Yucca Ridge Field Station near Fort Collins, Colorado using ground-based low-light video systems. We analyzed 36 sprites above the Nebraska MCS of August 6, 1994. The results lend further support to the hypothesis that sprites are almost uniquely associated with positive cloud-to-ground (+CG) lightning flashes. Sprite-associated +CGs also averaged substantially larger peak currents than the remaining +CG population (81 kA versus 30 kA in this storm system). There is some evidence that sprite-associated +CGs also have higher stroke multiplicity. This study yields no evidence of sprites associated with negative CG events. In the central United States an additional requirement appears to be that the parent MCS has a contiguous radar reflectivity area exceeding 20-25,000 km 2. The majority of the sprites occur above the large stratiform precipitation region and not the high-reflectivity convective core of the MCS. Triangulation of a limited number of paired images (from September 7, 1994) suggests that the sprite is generally centered within 50 km of the parent +CG. Assuming the +CG provides the range, single-image photogrammetric analyses provide estimates of the maximum vertical extent of the sprites. For this storm the sprite tops averaged 77 km with a maximum of 88 km. The bases averaged 50 km but with a few sprite tendrils extending as low as 31 km.
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This review considers the different models that have been developed to explain a class of phenomena that occur above lightning storms. These phenomena have been named elves, red sprites and blue jets. The elves appear between 90 and 70 km altitude and extend over several 100 km horizontally. They are visible for less than 0.1 ms. Red sprites cover a range of altitudes from 80 to 55 km with narrow tendrils extending below 55 km. Horizontally they are 20–30 km wide. Their visible lifetime is from a few to some tens of ms. Blue jets propagate from cloud tops (15 km) to an altitude of 40 km with a velocity of 100 km/s which gives a lifetime of 300 ms.In all of the models, the energy source is the electric fields associated with the lightning—the quasistatic fields due to the original charge distribution, the electromagnetic pulse due to the propagation of the return stroke or the quasistatic fields due to the charge redistribution by the currents. There are two different models to explain the heating of the neutral atmosphere by these electric fields. These models accelerate either the ambient thermal electrons (<eV) or high-energy, cosmic-ray-generated MeV electrons. These electrons in turn collisionally heat the neutrals and produce the heating, ionization and optical emissions.
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Measurements of ELF/VLF radio atmospherics (sferics) at Palmer Station, Antarctica, provide evidence of active thunderstorms near the inferred source regions of two different gamma-ray bursts of terrestrial origin [Fishman et al., 1994]. In one case, a relatively intense sferic occurring within +/-1.5 ms of the time of the gamma-ray burst provides the first indication of a direct association of this burst with a lightning discharge. This sferic and many others launched by positive cloud-to-ground (CG) discharges and observed at Palmer during the periods studied exhibit `slow tail' waveforms, indicative of continuing currents in the causative lightning discharges. The slow tails of these sferics are similar to those of sferics originating in positive CG discharges that are associated with sprites.
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The venerable field of gaseous electronics underlies the understanding of a lightning-like phenomenon of spectacular extent, shape, and color.
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Great Plains storms are known for their ability to produce severe weather. They are also prodigious producers of lightning; just how prodigious has been vividly illustrated by observations in central Oklahoma with a new Global Positioning System (GPS)-based lightning mapping system.The observations are useful not only for studying storm electrification but also provide a valuable indicator of storm structure and intensity.The system maps lightning in three spatial dimensions by measuring the times at which impulsive VHF radiation events arrive at a network of ground-based measurement stations. Low-cost GPS receivers provide sufficient timing accuracy to produce high-quality pictures of the total lightning activity over a large area.