SpritesSearch

A pair of spectra taken simultaneously by two different ground-based instruments has been analyzed by our group. As with previous observations, the spectra are composed primarily of the N-2 first positive group (1PG) (B(3)Pi(g) - A(3)Sigma(u)(+)). In a previous study, we compared the N-2(B) vibrational distributions from the spectral analysis with those resulting from a time-dependent kinetic model of N-2 triplet excited state populations. Both spectra reflect emission between 50 and 60 km. The higher-attitude spectrum is primarily 1PG but also shows the presence of features which appear to be N-2(+) Meinel (A(2) Pi(u) - X(2)Sigma(g)(+)). The lower-attitude spectrum shows little or none of the apparent Meinel emission but has an N-2(B) vibrational distribution similar to ones observed in laboratory afterglows. In this paper we discuss the apparent presence of the Meinel emission and present the observed N-2(B) vibrational distributions. (C) 2003 Elsevier Science Ltd. All !

Studies of sprite-producing lightning have revealed much of what we

Using telescopic imaging it is observed that sprite morphologies such as

The Biomass Burning and Lightning Experiment phase A (BIBLE A) aircraft

In situ aircraft measurements of O/sub 3/, CO, total reactive nitrogen

Recent spectral measurements of sprites and elves using imaging spectrometers have been limited to the red end of the spectrum (above 500 nm), while spectral information from the blue end of the spectrum has been measured only by bandpass-filtered photometers. Although the blue photometric data identified N-2 second positive and N-2(+) first negative band emissions, uncertainty remains in some measurements due to the small separation in the emission lines. Spectrally resolved measurements of the blue components, particularly the emissions of N-2(+) IN band, are very important because they indicate the existence of relatively high electron energies and high level of ionization at that altitude and therefore can be a great help in uncovering the generation mechanism for sprites. We have recently developed an intensified CCD slit spectrograph system with a peak sensitivity around 350 nm with a highly linear dispersion and a spectral resolution of 2 nm. (C) 2003 Elsevier Scie!

During the summer of 2000, the Severe Thunderstorm Electrification and

Mesospheric lightning-related sprites and elves, not attached to their parent thunderstorm's tops, are being joined by a family of upward electrical discharges including blue jets, emerging directly from thunderstorm tops.

The magnitudes of scattered fields produced during early/fast very low

Elves, halos and sprites were observed during August 1999 with a 1 ms high

For original paper see ibid., vol. 65, no.5, p.509-18 (2003); for comment

[1] Distant electric fields predicted by the transmission line (TL) model and by the modified transmission line model with exponential current decay with height (MTLE) are examined as a function of polar angle ( elevation) and return stroke propagation speed. The lightning return stroke current waveform was approximated by a step function. The resultant electric field waveform for the TL model is also a step function, while for the MTLE model the field instantaneously rises to the same value as for the TL model and then decays exponentially. The exponential current attenuation with height in the MTLE model results in a considerable reduction in the electric field intensity within 1 mus after the initial peak, particularly for smaller polar angles ( larger elevations) and higher propagation speeds. Combinations of current and speed ( as a function of polar angle) that are conducive to the production of transient optical emissions ( elves) in the lower ionosphere are examin!

We correlated cloudtop temperatures obtained from GOES-8 infrared images,

We present a detailed statistical analysis of the association of 40 sprite events with lightning from the parent thunderstorm. Both temporal and spatial criteria were used to identify the parent cloud-to-ground (CG) lightning. Sprite images were GPS time stamped and their locations triangulated. In contrast to previous reports of nearly one-to-one association of sprites with positive cloud-to-ground (+CG) lightning, 11 events (27%) did not have a +CG recorded by the National Lightning Detection Network (NLDN), and 7 events (17%) had neither NLDN nor very low frequency (VLF) signatures associated with them. A negative cloud-to-ground (-CG) preceded one of these events by 9 ms. As expected for similar to16.7 ins integrated images, none of the sprites without a +CG had any discernible visual characteristic that would distinguish them from

Waveform monitoring of ELF radio signals in the frequency range of 1-400 Hz have been carried out on a routine basis at Syowa station (69.0degreesS, 39.6degreesE in geographic coordinates), Antarctica since February, 2000. The main purpose of these observations is to monitor global lightning activity and to locate lightning-induced sprites and elves. The ELF observation system consisting of two search coil sensors (geomagnetic north south (H) and cast west (D) sensors) was installed at a remote unmanned observatory in West Ongul Island located 5 km southwest from Syowa station. As a back up system, the same system was installed near Syowa station in East Ongul Island. Signals from these sensors were digitally sampled at 1000 Hz with a GPS time code. On July 4, 2000 during the STEPS (Severe Thunderstorm Electrification and Precipitation Studies) 2000 campaign carried out over the Great Plains in the US, 57 sprite events were observed from Yucca Ridge Field Station (40.7deg!

We estimated locations and rates of sprite occurrences on a global scale

The present report investigates using simultaneous observations of

NO/sub x/ transport and production by lightning for 10 July 1996

Transient luminous events in the atmosphere, such as lighting-induced sprites and upwardly discharging blue jets, were discovered recently in the region between thunderclouds and the ionosphere. In the conventional picture, the main components of Earth's global electric circuit include thunderstorms, the conducting ionosphere, the downward fair-weather currents and the conducting Earth. Thunderstorms serve as one of the generators that drive current upward from cloud tops to the ionosphere, where the electric potential is hundreds of kilovolts higher than Earth's surface. It has not been clear, however, whether all the important components of the global circuit have even been identified. Here we report observations of five gigantic jets that establish a direct link between a thundercloud (altitude   16 km) and the ionosphere at 90 km elevation. Extremely-low-frequency radio waves in four events were detected, while no cloud-to-ground lightning was observed to trigger these events. Our result indicates that the extremely-low-frequency waves were generated by negative cloud-to-ionosphere discharges, which would reduce the electrical potential between ionosphere and ground. Therefore, the conventional picture of the global electric circuit needs to be modified to include the contributions of gigantic jets and possibly sprites.

Strong quasi-electrostatic fields (QESF) are generated in the ionosphere after positive lightning discharges by a succeeding redistribution of the induced spatial charges. These fields cause significant heating and modifications of both electron density and electric conductivity in the ionosphere. It is established that they also cause red sprites. According to recent observations, studying of initial period of QESF development is important for understanding sprite onset mechanisms. In the present paper QESF are modeled in these periods and the influence of different conditions on their structure is analyzed. First the structures of quasi-DC electric fields preceding a lightning discharge are investigated. The dependence of these structures on the magnetic field local orientation is taken into account by considering two latitudinal cases, corresponding to high and equatorial latitudes respectively. This is done analytically for each case. Then QESF are modeled which inten!

A discussion of lightning induced optical emissions in the ionosphere is presented. Emphasis is placed on accounting for the puzzling observation of the spatial structure in the optical emissions and the Sprite 'seeding' before the development of the 'tendrils' (or streamers). In this context we discuss the generation of spatial brightness variations, within the required lightning parameter thresholds, due to spatio-temporal electric fields and spatial neutral density perturbations.

Model simulations of tropospheric O₃ require an accurate specification

The optical emissions in a large number of bright sprites observed over one

A balloon campaign was conducted in boreal summer 1999 to measure the

While the fine structure in sprites can assume a wide variety of shapes,

Airborne in situ measurements of NO, NO/sub 2/, NO/sub y/, CO, CO/sub 2/,

A fascinating set of newly discovered complex phenomena indicate that thunderstorms and lightning discharges are strongly coupled to the overlying upper atmospheric regions. Lightning discharges at cloud altitudes (<20 km) affect altitudes >40 km either via the release of intense electromagnetic pulses. (EMPs) and/or the production of intense quasistatic electric (QE) fields. The intense transient QE fields of up to similar to1 kV . m(-1). which for positive CG discharges is directed downwards. can avalanche accelerate upward-driven runaway MeV electron beams. producing brief (similar to1 ms) flashes of gamma radiation. spectacular manifestation of these intense fields is the so-called 'Sprites'. large luminous discharges in the altitude range of similar to40 km to 90 km, which are produced by the heating of ambient electrons for a few to tens of milliseconds following intense lightning flashes. The so-called 'Elves' are optical flashes which last much shorter (< 1 ms) than sprites. and are typically limited to 80-95 km altitudes with much larger (up to 600 km) lateral extent. being produced by the heating, ionization, and optical emissions due to the EMPs radiated by both positive and negative lightning discharges.

In situ measurements of NO/sub y/, NO/sub x/, and temperature confirm that

We interpret the distribution of tropical tropospheric ozone columns (TTOCs)

Data from sprites using a 16-channel, multi-anode photometer (MAP) have been recorded at 0.1 ms resolution. The majority of the sprites have onsets at an altitude of 70-75 km and subsequently propagate both upward and downward from this initial altitude. The statistical lifetime of the emissions measured by the blue-sensitive MAP is approximately 1.3 ms. The velocities of propagation are between 10/sup 7/ and 10/sup 8/ m s/sup -1/, with larger velocities being measured at higher altitudes. The larger propagation velocities of the upward and downward sprite luminosity channels are consistent with the characteristics of highly over-voltage streamers in the mesosphere.

Sprite halos are brief, diffuse flashes, which occur at the top of a sprite and precede the development of streamer structures at lower altitudes. We have investigated the characteristics of sprite halos in detail using coincident photometric and imaging data obtained during the Sprites'96 and '99 campaign in Colorado and Wyoming, USA. It is found that the average altitude of the centroid of the halo emission and the mean horizontal diameter of the halo events are  80 and  86 km, respectively, while the average speed of the descending motion of the sprite halos was  4.3*10/sup 7/ m/s. It was also found that the peak current intensity of the causative CG decreases with time delay from the onset of the sferics.

Nonstationary electric fields of thunderclouds, which are created by these clouds after cloud-to-ground discharges in the atmosphere with exponential electrical conductivity, are calculated in an electrostatic approximation. The asymptotic expressions for the distribution of the vertical component of the electrostatic intensity, depending on time and atmospheric altitude along the axis of symmetry, have been obtained for the point and one-dimensional distributions of the initial cloud charge, as well as for the horizontal distribution of the cloud with a finite cylindrical radius. These results are used to determine the vertical component of the electrostatic intensity and the cloud charges necessary for initiating discharges between clouds and the upper atmosphere.

[1] During the EXL98 aircraft mission, sprites and blue jets were observed by narrow band cameras that measure the N-2(+) 1NG (0,1) band at 4278Angstrom and the N-2 2PG (0, 0) band at 3370Angstrom. We discuss the observations (similar to1 km resolution), instrumental and atmospheric corrections, and altitude profiles of ionized (1NG) and neutral (2PG) emission observed during a specific sprite. The ratio of ionized-to-neutral emission indicates a relative enhancement of ion emission below 55 km. Characteristic electron energies (E-Ch) and electric fields (E) are derived from these emission ratios using excitation rates computed from a model that solves the Boltzmann equation as a function of electric field. Up to 55km E follows the breakdown field (E-k) and E-Ch is similar to2.2eV. Above 55 km E drops below E-k and E-Ch drops to similar to1.75eV near 60km.

The University of Alaska deployed a high speed (1000 fps) camera at the Wyoming Infrared Observatory to observe sprites over Midwest U.S. thunderstorms as part of the 1999 NASA Sprites Balloon Campaign. Here we report on the velocity of development of downward spatial structures known as tendrils in several sprite events recorded during a large thunderstorm over eastern Nebraska the night of 18 August 1999. Downward tendril development occurred at velocities that varied by more than two orders of magnitude, ranging from  10/sup 5/ to >or=3*10/sup 7/ m/s. The tendrils progressed through multiple velocity regimes, typically in the order fast-slow or slow-fast-slow. Examples are presented of multiple sets of temporally distinct tendrils that develop from the same sprite event and tendrils that have a horizontal component of expansion.

The observed altitude stratification in large number of sprite events,

[1] Blue jets and blue starters are considered as positive streamer coronas expanding from the streamer zones of conventional lightning leaders under conditions when large-scale electric fields near the thundercloud tops exceed the minimum field required for the propagation of positive streamers in air. Results from a three-dimensional fractal model based on a phenomenological probabilistic approach to the modeling of streamer coronas indicate, in particular, that blue jets and blue starters can be formed by a fast (similar to1 s) accumulation of similar to110-150 C of positive thundercloud charge distributed in a volume with effective radius similar to3 km near the cloud top at similar to15 km. The model simulates the propagation of branching streamer channels constituting blue jets and blue starters as a three-dimensional growth of fractal trees in the electric field created by thundercloud charges and self-consistently accounts for the electric field effects due to the!

The majority of sprites, the most common of transient luminous events (TLEs) in the upper atmosphere, are associated with a sub-class of positive cloud-to-ground lightning flashes (+CGs) whose characteristics are slowly being revealed. These +CGs produce extremely low frequency (ELF) and very low frequency (VLF) radiation detectable at great distances from the parent thunderstorm. During the STEPS field program in the United States, ELF/VLF transients associated with sprites were detected in the Negev Desert, Israel, some 11000 km away. Within a two-hour period on 4 July 2000, all of the sprites detected optically in the United States produced detectable ELF/VLF transients in Israel. All of these transients were of positive polarity (representing positive lightning). Using the VLF data to obtain the azimuth of the transients, and the ELF data to calculate the distance between the source and receiver, we remotely determined the position of the sprite-forming lightning with an average locational error of 184 km (error of 1.6%).

With the recent introduction of the Canadian Lightning Detection Network

We have recently shown that a negative streamer in a sufficiently high

The breakdown of rarefied air under conditions of electron cyclotron resonance (ECR) at a frequency of 2.45 GHz in a mirror trap is analyzed in order to find a runaway electron breakdown (REB) regime considered as a mechanism for generating gigantic discharges in the stratosphere-red sprites. It has been found that both usual and anomalous ECR discharges are observed in the region where pressures are lower than 10(-3) torr. The anomalous discharge has thresholds that are higher by a factor of 4-5 and generates an intense pulse-modulated gamma-emission, which is a bremsstrahlung for electrons accelerated to subrelativistic energies of 100-300 keV in relatively weak microwave fields of 5-20 V/cm. The gamma-emission is accompanied by cyclotron radiation at the second harmonics of the microwave generator frequency, which indicates that electrons with energies of about 10 keV are present in the system. The front of the anomalous ECR discharge considerably-by not less than 80 m!

Recent observations of optical phenomena above an active lightning discharge such as red sprites, blue jets, blue starters and elves have refocused interest in this field and its consequences. It is argued that during lightning discharge ELF, VLF and optical emissions are generated. Analyzing the recorded data it is clearly shown that intense ELF generation from positive cloud to ground lightning discharge is an indication of the presence of red sprite. Daytime observation of red sprite is difficult and hence ELF waves can work as an indicator. The diagnostic features of ELF and VLF waves are also discussed and interesting results based on the analysis of whistlers recorded at Indian stations are presented. Recently, association of VLF waves with earthquakes and red sprites are reported. We have briefly summarized some results related with these phenomena.

A global three-dimensional model of tropospheric chemistry driven by

Sprites were observed over thunderstorms in the southern China and in oceans around Taiwan. The observation sites were on the Ali Mountain of Taiwan's Central Ridge area with an altitude of 2413 m and in the campus of National Cheng Kung University with an altitude of 50 m. For the observed land sprites, 90% of them were either carrots or columniforms and 64% of the sprites occurred in groups. Among the observed oceanic sprites, 89% of them were carrots but only 22% of the sprites occurred in groups. We define a sprite active system as a thunderstorm that continuously produces at least one sprite in a 10-minute interval. The active sprites generating periods for the observed thunderstorms were typically shorter than 30 minutes. The sprite production rates for these Asian thunderstorms are estimated to be between I approximately=2*10/sup -4/ events/km/sup 2//hr and I approximately=1*10/sup -3/ events/km/sup 2//hr.

The transient ELF ( 50-5000 Hz) magnetic field radiated by lightning

In situ trace gas (O/sub 3/, NO, NO/sub 2/, NO/sub y/) and ultrafine aerosol

Confusion in the interpretation of s andard-speed video observations of

The production of NO/sub x/ by lightning over the contiguous United States

DSRI has initiated a development program of CZT X-ray and gamma-ray detectors employing strip readout techniques. A dramatic improvement of the energy response was found operating the detectors as the so-called drift detectors. For the electronic readout, modern ASIC chips were investigated. Modular design and the low-power electronics will make large area detectors using the drift strip method feasible. The performance of a prototype CZT system will be presented and discussed. One such detector system has been proposed for future space missions: the X-Ray Imager (XRI) on the Atmospheric X-ray Observatory (AXO), which is a mission proposed to the Danish Small Satellite Program and is dedicated to observations of X-ray generating processes in the Earth's atmosphere, Of special interest will be simultaneous optical and X-ray observations of sprites that are flashes appearing directly above an active thunderstorm system. Additional objective is a detailed mapping of the auroral X-ray and optical emission, XRI comprises a coded mask and a 20*40 cm/sup 2/ CZT detector array covering an energy range from 5 to 200 keV.

The purpose of this paper is to model numerically the ionisation created in the mesosphere above a strong horizontal (cloud-to-cloud) lightning discharge, and thus to understand better the formation of elves and related columniform (spatially structured) sprites. Such ionisation depends upon height, via the ratio of the VLF/LF wave electric field (radiated by the current in the discharge) to the atmospheric neutral density. The simulation shows local maxima on the order of 10 km apart due to the interference between direct waves radiated by the discharge current, waves reflected by the ground and waves reflected by the ionosphere. Parametric studies are carried out varying the frequency, amplitude, height, length and duration of the current. For waves greater than or equal to 30 kHz generated by a current greater than or equal to 50 kA, localised peaks of electron density occur from 75 to 85 km altitude, particularly for discharges longer than 15 km. From such peaks, time!

A network of three time-synchronized high-precision induction coil magnetometers is installed in North America to measure sprite-associated lightning flash waveforms in the frequency range 0.1-1000 Hz during the Energetics of Upper Atmosphere Excitation by Lightning 1998 sprite campaign in July 1998. Simultaneous intensified video observations on board an aircraft are used to investigate 16 sprites with long time delays >33.33 ms relative to the parent lightning discharge reported by the National Lightning Detection Network. Three different long-delayed sprite-associated waveforms can be distinguished: 38% do not exhibit any significant magnetic intensity variation, 25% exhibit slow variations  100 ms, and 25% exhibit short pulses  4 ms. The source locations of the sprite-associated short pulses are triangulated by use of arrival time difference analysis. One source location exhibits a substantial spatial displacement  60 km relative to the parent lightning discharge, in agreement with the azimuths of sprite luminosity edges determined from the corresponding background star field of the video observations on board the aircraft. It is concluded from the temporal and spatial coincidence of the secondary short pulse and the sprite luminosity that this particular sprite is associated with current in the mesosphere.

Red sprites and elves were observed in Japan during the winter of 1998/99 in Hokuriku region by the group of Tohoku University. The authors analyze quantitatively the results from coordinated measurement consisting of ELF transients, VLF subionopheric disturbances and lightning discharges associated with the optical events. They find the clear straightforward relationship between charge transfer of the parent discharge calculated from ELF (f<15 Hz) and the ionospheric disturbances regardless of the types of optical events indicating significant atmosphere-mesosphere-ionosphere coupling. Sprites tend to associate with a large ionospheric disturbance (-13 +4.6 dB) with a large charge transfer (52 175 C), whereas a large lightning peak current (+223 +470 kA) (or slow-tail amplitude) leading to the strong EMP is necessary to initiate elves, but with rather small ionospheric disturbances.

Simultaneous in situ measurements of NO, NO/sub y/, HNO/sub 3/, CO, CO/sub

The presence of energetic runaway electron beams above thunderstorms is

The development of upward propagating avalanches of runaway electrons in electric and geomagnetic fields above stratiform thunderclouds has been simulated. It is assumed that the quasistationary electric field above the cloud was generated by a lightning, which transferred the negative charge to the cloud top. The avalanche of background electrons has been calculated for an altitude of 30 km and higher, where the electric field was stronger than the threshold (for runaway electrons) electric field. It has been shown that, in the considered cases, the avalanche either faded or slightly developed: the amount of runaway electrons increased by a factor of 3-4, which is insufficient for an initiation of the recently revealed high-altitude (30-80 km) optical flashes called red sprites. The strong dependence of the obtained results on the values and mutual direction of the electric and geomagnetic fields has been corroborated. For example, the horizontal magnetic field (50 mu T) perpendicular to the electric field excludes the development of an avalanche and even the removal of a primary electron with an energy of 2 MeV from a starting point. If the geomagnetic field (50 mu T) is strictly vertical and parallel to the electric field, the avalanche develops slowly (as in the case with no magnetic field) and has a considerably smaller cross section.

Results from a new three-dimensional fractal model of sprites as well as recent experimental data on thundercloud charge moment changes associated with sprites indicate that ionized regions in sprites can sometimes reach thundercloud tops, creating favorable conditions for establishing a highly conducting link between the Earth's surface and the lower ionosphere.

The impact of lightning on tropospheric reactive nitrogen NO/sub x/

Sprite halos have been identified as an impulsive but spatially diffuse

The venerable field of gaseous electronics underlies the understanding of a

We show that ubiquitous small conducting particles of meteoric origin in the mesosphere and stratosphere may explain some features of sprite occurrence and fine structure. The main processes involved are: electrostatic field amplification by microspires on the dust surface

The relative importance of various odd nitrogen (NO_y) sources

Recent time-resolved multi-color photometric data obtained on one class of lightning-related transient upper-atmospheric electromagnetic events called sprites have confirmed an impulsive ionization emission during the sprite initiation. Data have also been obtained on some sprites which do not exhibit observable tendrils and which exhibit ionization emission that, if present, is below the authors' detection limit. This suggests that some sprite events exhibit strong ionization while others do not. These results indicate that conditions causing sprite optical emissions are highly variable.

Discusses NO/sub x/ together with associated chemically coupled species in

A large spark generator was used outdoors to determine the production of

Airborne observations of NO during the Subsonics Assessment Ozone and

Observations of extremely low frequency (ELF) radio atmospherics (sferics),

Understanding lightning NO/sub x/ (NO+NO/sub 2/) production on the cloud

Telescopic images of sprites show a wide variety of generally vertical but also slanted fine structure, including branching tree-like shapes and well defined but isolated columns, with transverse spatial scales ranging from tens of meters to a few hundred meters at  60-85 km altitude. Simultaneous analysis of radio atmospheric and lightning data indicates that specific columnar regions are selectively excited by successive discharges.

Sprites, a form of brief luminous discharge in the upper atmosphere above a thunderstorm, were observed and imaged on two video cameras in Australia's Northern Territory. These were the first such ground-based observations made outside the United States. Sprite discharges typically took place between the altitudes of 50 km and 80 km and spanned an average width of 44 km. Many of the sprite events were of long duration, with an average of 145 ms. These spatial and temporal features were similar to those observed from the ground and the air in the United States. During the longer events, some luminous discharge elements were observed to decay as other new elements formed. As the new elements were often laterally displaced from the old, the sprites sometimes appeared to dance across the sky. This phenomenon has been observed in Colorado and named

NO/sub x/ (NO and NO/sub 2/) and ozone were measured on 98 flights during

Concurrent measurements from the CSU-CHILL multiparameter Doppler radar, the

The intense plasma perturbations in the middle atmosphere, produced by the high-altitude discharges and appearing as luminescent columns

The impact of NO/sub x/ from aircraft emissions, lightning, and surface

The study of the global atmospheric electric circuit has advanced dramatically in the past 50 years. Large advances have been made in the areas of lightning and thunderstorm research. The authors now have satellites looking down on the Earth continuously, supplying information on the temporal and spatial variability of lightning and thunderstorms. Thunderstorms are electric current generators, which drive electric currents up through the conducting atmosphere. They maintain the ionosphere at a potential of  +250 kV with respect to the Earth's surface. The global electric circuit is completed by currents  2 pA/m/sup 2/ flowing through the fair weather atmosphere, remote from thunderstorms, and by transient currents due to negative cloud-to-ground lightning discharges. The time constant of the circuit,  >2 min, demonstrates that thunderstorms must occur continually to maintain the fair weather electric field. New discoveries have been made in the field of sprites, elves and blue jets, which may have a direct impact on the global circuit. Our knowledge of the global electric circuit modulated by solar effects has improved. Changes to the global circuit are associated with changes of conductivity linked with the time-varying presence of energetic charged particles, and the solar wind may influence the global electric circuit by inferred effects on cloud microphysics, temperature, and dynamics in the troposphere. We now have a better understanding of how the conductivity of the atmosphere is influenced by aerosols, and bow this impacts our measurements of the fair-weather global circuit.

Measurements of electric fields associated with thunderstorms and lightning were obtained during two balloon flights carrying double-probe electric field detectors launched from Cachoeira Paulista (22 degrees 44'S, 44 degrees 56'W), Brazil, on January 26, 1994, and March 23, 1995. From data obtained in 1994, a linear relationship between the quasi-dc vertical electric field peak amplitude and the decay time constant of lightning signatures was found for negative flashes. The results are compared to similar data for intracloud flashes. Based on electric field data obtained in 1995 and on the present knowledge about the differences between positive cloud-to-ground and intracloud flashes, two methods to distinguish them at balloon altitudes are presented: The first is based on an estimate of the destroyed charge in the event; the second is based on the peak amplitude ratio between the vertical quasi-de and the VLF electric field. The behavior of the vertical quasi-de electri!

On August 14, 1998, 3 separate daytime sprite events were detected via a unique extremely low frequency (ELF) sprite signature. The onset of the sprite ELF signatures was delayed by 11.0-13.2 ms from positive cloud-to-ground strokes which had attained exceptionally large charge moment (charge times height) changes of 3900-6100 C.km. It is shown that a charge moment change of 6100 C.km may have been sufficient for conventional breakdown at similar or equal to 54 km altitude, assuming an experimentally measured ion: conductivity profile of Holzworth et al., [1985]. The daytime sprites themselves contained unusually large charge moment changes of similar or equal to 2800 C.km, similar or equal to 1200 C.km, and similar or equal to 910 C.km.

Images of sprites have been recorded at 1 ms resolution revealing several new sprite properties. Sprites appear to occur in a highly structured mesosphere, and the authors suggest that the cause of some of this structure is the sprite activity itself. Evidence is seen in events where a subsequent nearby sprite appears to re-activate the volume of a previous sprite, in sprites where tendrils and branches develop away from the normally observed vertical direction, and in beads that lasts much longer that the parent sprite. Sprites can be large with horizontal widths of more than 40 km and can extend from the clouds up to the lower ionosphere thus affecting a large volume of the atmosphere. The total horizontal area of sprites during one storm over Nebraska was a significant fraction of the area covered by the associated thunderstorm raising the possibility of larger scale measurable mesospheric effects.

The distribution of reactive nitrogen species over the South Pacific during

In order to investigate the spatial and temporal variations of sprites and elves and their spectral structures, we have carried out photometric observations during the SPRITES' 97 campaign using two multi-anode array photometers (MAPs). Each MAP has 5 fields of view arrayed in vertical and a time resolution of 52 ps, which enables us to detect the rapid vertical motion of sprites/elves. Since the emissions of sprites and elves mainly consist of the Ist and 2nd positive bands of N-2, the intensity ratio of these bands gives us information on the energy distribution of electrons which excite N-2 molecules via collision processes. Thus, one of the MAP instrument with an optical sharp cut filter was used to measure only the N-2 Ist positive band emissions in the wavelength range of 560 - 800 nm, while the other MAP without a filter was used to measure both the N-2 Ist and 2nd positive band emissions in the range 350 - 800 nm. Comparing the data from these two MAPs, we estimat!

This paper reveals a possible connection between lightning activity and the

High altitude air breakdown, manifested as

A global 3-dimensional chemical tracer model (CTM) has been used to

We analyze synchronized high speed video images and ELF-VLF radio emissions

This paper investigates the role of lightning in the production of nitrogen

A three-dimensional Monte Carlo model of the uniform relativistic runaway

A model of gamma -ray flashes is presented. The model relies upon a

Deduces temporal variations of the level of global lighting activity from

The authors present an analytical time domain solution for ELF

Deduces temporal variations of the level of global lighting activity from

Red sprites consist of multiple ionised columns extending above a thunderstorm from  30 km to  90 km. Electron densities in these columns are very much larger than the ambient background, perhaps fives orders of magnitude at 70 km. These highly ionized structures cause observable perturbations in subionospheric VLF transmissions known as

An investigation is made of the influence of changes in atmospheric pressure with altitude and the thundercloud geometry on the development of lightning propagating upward to the ionosphere. It is shown that the mechanism for the development of high-altitude lightning does not differ from that for the formation and propagation of ordinary lightning between a thundercloud and the ground. It is established that high-altitude lightning forms as a result of a reduction in pressure with altitude and can only take place from thunderclouds located at high altitudes.

Broadband ELF/VLF measurements of sferics near Ft. Collins, Colorado,

In situ measurements of cloud properties, NO, and other trace gases were

Video and photometric observations of a meteor-triggered

Ground based zenith sky measurements of O/sub 3/ and NO/sub 2/ slant optical

The results of numerical simulations of red sprite discharges, namely the temporal evolutions of optical emissions, are presented and compared with observations. The simulations are done using the recently recalculated runaway avalanche rates. The temporal evolution of these simulations is in good agreement with ground-based photometer and CCD TV camera observations of red sprites. The authors' model naturally explains the

In July-August, 1996, Stanford University carried out broad and ELF/VLF

The sequence of videotape observations of the upper atmospheric optical flashes called sprites, jets, starters, and ELVES are described in the successive phases of search, discovery, confirmation, and exploration for the years before 1993. Although there were credible eyewitness accounts from ground observers and pilots, these reports did not inspire a systematic search for hard evidence of such phenomena. The science community would instead wait for serendipitous observations to move the leading edge of this science forward. The phenomenon, now known as a sprite, was first accidentally documented on ground based videotape recordings on the night of 6 July, 1989. Video observations from the space shuttle acquired from 1989-1991 provided 17 additional examples to confirm the existence of the sprite phenomenon. Successful video observations from a mountain ridge by Lyons, starting on 7 July, 1993, and night-time aircraft video observations by Sentman and Wescott on 8 July, 1993 established the basic science of the sprite phenomena by acquiring and analyzing data based on hundreds of new events. The 1994 Sprites campaign and the video entitled

Continuous measurements of nitrogen oxide and ozone were performed from a

Computer simulations are carried out to study the `sprite' onset mechanism. Both electrostatic and electromagnetic codes are developed to calculate the electric field structure and optical emission intensity between the top of the thundercloud and the ionosphere. The optical emission is composed of two structures. One peaks at 70 km height and its lateral dimension is 50-60 km and the other peaks at 90 km height and the lateral dimension extends beyond 200 km. It is found that the nitrogen first positive band, which has a red colour, dominates over the nitrogen second positive band except at the bottom of the optical emission. The upper part of the optical emission is caused by a horizontally travelling electromagnetic pulse induced by a lightning discharge current. The lower structure is caused by electrostatic effects induced by the unneutralized charge left after the lightning discharge current flows. The electromagnetic codes developed can simulate the self-consistent response of the upper atmosphere to the lightning discharge current. The electrostatic treatment can predict only the optical emission at heights less than  80 km. The optical emission intensity has a strong nonlinear dependence on the electric field strength through the enhanced electron density, and is increased for a long discharge path, a large current, and a short pulse. Also, the higher the lightning discharge is initiated, the brighter the optical emission is, because the electrostatic field is stronger for high altitude lightning.

Measurements of ELF-radiating currents associated with sprite-producing

The authors describe the terrestrial excitation of horizontal magnetic field

Long distant electric fields (400-500 km), generated by 26 positive cloud-to-ground flashes, were analysed. These flashes consist of well detectable long impulse fields subsequent to the initial peak. These hook-shaped slow fields are of considerable amplitude and have a mean duration of 1.24 ms. The amplitude of the long impulse field and the initial peak of the field show an approximately linear relationship. The long impulse current pertinent to positive return strokes which give rise to the measured long impulse fields were estimated. Flashes with these slow fields lower a mean charge of 50 C within the first 3 ms (excluding the first 100 mu s which contains the initial peak), whereas the maximum charge lowered is 124 C. The mean of the ratio between the peak of the long impulse field and the initial peak is 41%. The authors also estimated the fields that will be generated by the long impulse currents at distances of 1000 km, 3000 km and 5000 km from the strike. The estimated peak magnetic fields at 5000 km have a mean of 52 pT. The peak magnetic fields observed at distances of about 5000 km from positive lightning flashes, which were associated with red sprites, are in the same range as the peak magnetic fields that the authors have calculated for the above 26 flashes. Hence the authors conclude that the observed Q-bursts which coincide with the occurrence of red sprites are due to the long impulse currents of positive return strokes. This slow field variation is rarely observed in connection with negative return strokes. Even when it is present, in the event of a negative return stroke, the amplitude and the duration of the tail are much less than those of its counterpart in positive return strokes. This explains why ionospheric lightning is predominantly associated with positive return strokes but not with negative return strokes.

First airborne NO/sub x/ (NO+NO/sub 2/) measurements in anvils of active

Electromagnetic data recorded in conjunction with the Sprites '95 campaign are presented. The primary data set consists of electric and magnetic field waveforms related to visually identified sprites and elves recorded on the night of 24-25 July 1995. The data were collected near State College, PA, from a mesoscale convective system (MCS) located about 2100 km away near Lubbock, TX. The optical events were visually identified from an observation station in Fort Collins, CO. Presented are the waveforms of the sferics, a description of the measurement system, and a discussion of the signature traits of optical event-producing sferics. All of the sferics recorded which were related to visually identified events exhibited primarily unipolar `slow tail' electromagnetic signatures of order one millisecond duration in the direction indicating positive lightning. Similar waveforms of opposite polarity, indicating ordinary negative lightning, were not accompanied by any observed high altitude optical events.

A synthetic spectrum of red sprites due to electron energization by the

A model of the 4.26 mu m infrared emission due to red sprites is presented.

The time domain electric field produced by the model lightning discharges in

Analyzes the propagation of electromagnetic waves in the ELF. The authors

Charge and current systems associated with sprites constitute a part of the

Upper tropospheric NO/sub x/ controls, in part, the distribution of ozone in

The authors have constructed profiles of lightning NO/sub x/ mass

It has been suggested that optical flashes observed in the upper atmosphere above giant thunderstorms (red sprites) are due to streamers. Such streamers are initiated in the lower ionosphere by electron patches caused by electromagnetic radiation from horizontal intracloud lightning and then develop downward in the static electric field due to the thundercloud. The triggering conditions of streamer development are analysed. Using similarity relations, known characteristics of streamer tips obtained earlier in laboratory conditions are extended to a description of streamers in rare air. Streamer growth in the nonuniform atmosphere is calculated. It is shown that streamers first appear at a height of about 80 km and then grow downward to slightly below 50 km, where they are terminated. This is in agreement with red sprite observations. An altitude distribution of the streamer generated plasma is obtained. The simple models of streamer development presented in this paper could be applied for computations of streamers growing in other conditions.

A new and improved model of red sprites is presented. Emphasis is placed on

The global distribution of ozone in the troposphere and lower stratosphere

This paper reports observations of a distinctive form of sprites associated

Blue jets are narrow cones of blue light that appear to propagate upward

The close association of mesospheric sprites with positive ground flashes has led to the frequent assumption that positive charge is transferred from the top of a thunderstorm with positive-over-negative charge structure, from an altitude of 10 km or higher. Electrical and meteorological observations are reviewed which support a different picture: sprites are produced by laterally extensive mesoscale convective systems (MCS) in which the positive charge reservoir predominates in the 4-6 km ranges of altitude. The behaviour of the surface electric field during the End-of-Storm Oscillation and the behaviour of the vertical electric field above MCS during positive ground flashes both suggest a predominant in-cloud dipole moment with opposite polarity to that of the ordinary thundercloud. Lightning charge transfers of a few hundred Coulombs from the 4-6 km height range may be required for consistency with theories for sprite optical intensity and to account for ELF Q-burst intensity.

Video images, and photometric and VLF data, were obtained by the University of Minnesota SKYFLASH system of 38 `sprite' events associated with a strong frontal system located in the upper midwest, U.S.A., on 20-21 June 1996. Besides two image-intensified TV cameras, the SKYFLASH system included telescopic photometers sensitive to Rayleigh scattered lightning flashes by viewing the zenith over the station (O'Brien Observatory, University of Minnesota, about 40 km NE of Minneapolis-St Paul) and also several VLF channels with 300 Hz to 10 kHz bandwidth for recording the electromagnetic `sferics'. The sprites covered a wide range of sizes, from small kilometer-size filaments to huge luminous objects 50-60 km in lateral dimension. All the sprites appeared to consist of bundles of filaments, and always followed-within several ms-a `trigger' could-ground discharge which, in 35 of the 38 events, was positive. It is difficult to find physical mechanisms that explain this positive stroke preference. The larger events reached from 80 km almost to cloud tops, but the small events were localized near 60 km altitude, which is the `bright' region of sprite luminosity, a fact also not well explained theoretically. The filamentary structure of sprites also presents challenges to explain. Of about a dozen lightning storms observed with SKYFLASH in the period from 1993 to 1996 in the upper midwest, only two had an appreciable number of sprites.

Transient high altitude optical emissions referred to as

Streamers are a mode of dielectric breakdown of a gas in a strong electric

In the free troposphere, injection from the stratosphere, emissions at the

A quantitative self-consistent model of the processes determined by the

A new model of artificial airglow due to ionospheric modification is

A quantitative self-consistent model of the processes determined by the

Latitudinal distributions of NO, NO/sub y/, O/sub 3/, CO, CH/sub 3/I and

Once dismissed as figments of pilots' imaginations, strange flashes

A synthetic spectrum of red sprites due to electron energization by the electric field from lightning is computed by using the electron energy spectrum obtained from a Fokker-Planck code, which includes various inelastic losses. The results are compared with observed sprite spectra. Implications to models of red sprites are presented.

The authors have analyzed the Burst and Transient Source Experiment (BATSE) high-resolution timing data for 13 terrestrial gamma flashes (TGFs) to better characterize this newly identified phenomenon, which may be related to atmospheric lightning. They find that the minimum timescale for TGF variability is  25-250 mu s, with 50 mu s near typical. In general, TGFs are spectrally much harder than cosmic gamma ray bursts (GRBs). They additionally find that as with GRBs, individual pulses within a TGF tend to peak earlier at higher energies. This time-asymmetry rules out models such as sweeping beams. They also find that different pulses can have different spectra, with spectra typically softening as a pulse progresses. Event-averaged spectra for the TGFs were examined and found to be better fit in the 25-500 keV range by a power law than by a blackbody model. However, in general, even a power law is not a perfect fit. They find correlation between minimum TGF timescale and the power law spectral index, with rapidly varying TGFs appearing softer. From empirical comparisons of timescales and structures they speculate that if TGFs are somehow related to known high-atmospheric lightning events, then they are more probably related to red sprites than to blue jets or transionospheric pulse pairs.

Large area multicell thunderstorms lead to the formation of vertically

Quasi-electrostatic (QE) fields that temporarily exist at high altitudes following the sudden removal (e.g., by a lightning discharge) of thundercloud charge at low altitudes lead to ambient electron heating (up to  5 eV average energy), ionization of neutrals, and excitation of optical emissions in the mesosphere/lower ionosphere. Model calculations predict the possibility of significant (several orders of magnitude) modification of the lower ionospheric conductivity in the form of depletions of electron density due to dissociative attachment to O/sub 2/ molecules and/or in the form of enhancements of electron density due to breakdown ionization. Results indicate that the optical emission intensities of the 1st positive band of N/sub 2/ corresponding to fast ( 1 ms) removal of 100-300 degrees C of thundercloud charge from 10 km altitude are in good agreement with observations of the upper part

This paper begins a study on the role of lightning in maintaining the global

For pt.1 see ibid., vol.102, no.D5, p.5929-41 (1997). The global atmospheric

ELF waveforms at large distances from strong CG (cloud-to-ground) discharges are evaluated in the framework of Greifinger's night-time propagation model. It is shown that if the CG discharges triggering red sprites involve, as now generally accepted, >/sub  /10/sup 2/ C of charge then they should generate remote ELF atmospherics with considerably larger magnitudes than measured in the upper ELF (>300 Hz) range.

The authors derive exact expressions for remote electric and magnetic fields

A new and improved model of red sprites is presented. Emphasis is placed in accounting for the puzzling observation of the spatial structure in the red sprite's optical emissions. The model relies upon a horizontal fractal lightning discharge, which generates the EMPs that excites the optical emissions in the lower ionosphere. It is shown that the fractal model may account for the observed sprite's spatially structured optical pattern, while reducing the typical charge threshold to approximately 100 C.

Video images of the CRRES G1, G9, and G11A barium releases made at 400-500

Streamers often constitute the first stage of dielectric breakdown in strong

Horizontal magnetic field variations in the frequency range of the Earth

This paper generalizes the theory of the electron runaway and runaway

Measurements of ELF/VLF radio atmospherics (sterics) at Palmer Station,

The global distribution of NO/sub x/ in the troposphere is calculated using

A three-dimensional study of the relative importance of the different odd

The spatial and temporal distribution for a global three-dimensional, time

Transient luminous events (sprites, blue jets, elves) above large mesoscale

The authors 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 kV m/sup -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. The authors 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 nC m/sup -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. The authors' 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 kV m/sup -1/ and this field may be important in the global electrical circuit because the stratiform clouds have large horizontal extents ( 10/sup 4/ km/sup 2/).

Temporal variations of the global lightning activity were deduced from long

Quasi-electrostatic (QE) fields which exist above thunderclouds after lightning discharges can lead to the formation of columnar channels of breakdown ionization and carrot-like vertical luminous structures with typical transverse dimension  5-10 km spanning an altitude range from  80 km to well below  50 km. The carrot-like forms closely resemble those observed in sprites. Results indicate that the appearance of optical emissions can be significantly delayed in time ( 1-20 ms) with respect to the causative lightning discharge.

Radio atmospherics launched by sprite-producing positive cloud-to-ground lightning flashes and observed at Palmer Station, Antarctica, exhibit large ELF slow tails following the initial VLF portion, indicating the presence of continuing currents in the source lightning flashes. One-to-one correlation of sferics with NLDN lightning data in both time and arrival azimuth, measured with an accuracy of +or-1 degrees at  12,000 km range, allows unambiguous identification of lightning flashes originating in the storm of interest. Slow-tail measurements at Palmer can potentially be used to measure continuing currents in lightning flashes over nearly half of the Earth's surface.

In July and August of 1989 the National Center for Atmospheric Research

The origins of mysterious gamma -ray and radio flashes recently detected by satellite-based instruments passing over thunderstorms are examined in the context of upward propagating discharges initiated by runaway air breakdown. Preliminary calculations normalized by the recent optical measurements of so-called sprites indicate that the runaway mechanism may well be the source of these emissions. If this is true, then upward discharges represent the first known manifestation of a fundamental, new process in plasma physics.

The mechanism of production of nitrogen oxides by electrical discharges has

A model is proposed for blue jets [Sentman and Wescott, 1995 and Wescott et al., 1995], which explains their dynamics, in particular the jet vertical velocity of about 100 km/s, the terminal altitudes of about 40-50 km, and the competitive occurrence of blue jets and the recently discovered blue starters [Wescott et al., 1995]. A blue jet is considered to be formed by an attachment-controlled ionizing wave, which moves upward via an electron avalanche in the wavefront due to the mainly vertical, downward directed quasi-electrostatic field, caused by the extraordinarily large (>100 degrees C) charge transfer in a high-altitude intracloud discharge or in a positive cloud-to-ground discharge with a long continuing current.

gamma -ray flashes of atmospheric origin as well as blue jets and red sprites are naturally explained by high-altitude discharges produced by runaway air breakdown. The authors present the first detailed model of the development of upward propagating discharges and compute optical and gamma -ray emissions that are in excellent agreement with observations. According to their theory, such discharges represent the first known manifestation of runaway air breakdown, a fundamental new process in plasma physics.

On February 26, 1995, during a NASA sponsored mission to Peru to study red

Documents the first observations of a new stratospheric electrical

New observations of sprites (cloud-ionosphere luminous discharges above thunderstorms) were made from the Yucca Ridge Field Station 20 km northeast of Fort Collins, Colorado, on the night of July 11-12, 1994, as part of a summer 1994 observing campaign. The sprites appeared above a moderate mesoscale convective complex mostly over Kansas at a range of about 270 km. The sprites were observed with both wide-field and telescopic image-intensified CCD TV cameras, a telescopic photometer system, and a 1- to 50-kHz band VLF sferics receiver. This paper is based on five 1-s data intervals containing bright sprites, smaller sprites, and cloud and sky flashes. Telescopic TV images of bright sprites had a fan-shaped upper plume with very fine features not well resolved by the TV, but dendritic (upward forked) and vertically striated forms adjacent to these plumes and bright points of luminosity around the plume-shaped regions. Many sprites consisted entirely of groups of vertically aligned striations which sometimes appeared to diverge from a common point of origin at cloud tops. All sprites in the present data sample were preceded by a cloud to ground (CG) stroke with a coincident sferic and sky flash. All CG strokes associated with sprites were positive, and most were 100 kA or more inferred peak current. From the photometer, the duration of the CG-induced sky flashes was about 3 ms and the additional sprite total light curve was also about 3 ms. The puzzling feature that the total duration of TV images of sprites was often longer than the photometric values is discussed and an explanation given. The sprites were attributed to strong negative charging, following the positive CG stroke, of a localized cloud top region which produced an intense electric field and a luminous discharge in the cloud-ionosphere region. The concept of

An analysis of the data obtained during AASE II was made to characterize

Summary form only given, as follows. The amplitude and phase of

Summertime distribution of lightning over the United States and the

VLF perturbations on signals propagating along great-circle-paths (GCP)

Imagery and spectra of high altitude luminous flashes, otherwise known as

Past and recent observations indicate the presence of lightning at altitudes

An analysis is performed on the heating of electrons in the lower ionosphere

Quasi-electrostatic fields that temporarily exist at high altitudes

Fleeting columns of luminosity occurring above large thunderstorms at 50-90 km altitude, presently known as sprites, were imaged with an intensified video charge coupled device (CCD) camera during a July 1995 ground-based campaign near Fort Collins, Colorado. These unfiltered intensified images reveal detailed spatial structure within the sprite envelope. The temporal resolution of standard interlaced video imagery is limited by the 60 fields per second acquisition rate (16 ms). The specific CCD used, however, is subject to bright events leaking into the readout registers, allowing time-resolution on the order of the linescan rate (63 mu s). Typical sprite onset is found to follow the associated cloud lightning by 1.5 to 4 ms. The onsets of the individual sprites within a cluster are generally, but not always, simultaneous to within 1 ms. Sprites tend to have a bright localized core, less than 2 km in horizontal dimension, which rises to peak intensity within 0.3 ms and maintains this level for 5 to 10 ms before fading over an additional 10 ms.

Low light level monochrome television observations obtained from the ground

For pt.1 see ibid., vol.22, no.10, p.1205-8 (1995). Initial observations of

During the night of 9-10 August 1993 more than 150 luminous cloud-ionosphere discharges (CIs) were observed above a thunderstorm complex moving SE across the state of Iowa. Images of the CIs were obtained through clear air by intensified CCD TV cameras at the O'Brien Observatory of the University of Minnesota located about 60 km NE of Minneapolis and 250-500 km from the storm center. The discharges consisted of bright vertical striations extending from 50-80 km altitude, often covering tens of kilometers laterally, with tendrils of decreasing intensity visible for the brighter events down to cloud tops below 20 km altitude. All the more intense CIs were coincident with a VLF sferic in the 300 Hz-12 kHz range, but small events often did not yield a detectable sferic. There is no unambiguous evidence that CIs were sources of sferics. Some of the CIs were observed to be coincident with a cloud brightening and with a cloud-ground stroke recorded by the National Lightning Detection Network. The duration of the images was generally less than one TV field (<16.7 ms). Many of these discharges have now been observed by the space shuttle, by aircraft-borne TV cameras and a large number by a ground-based camera observations in Colorado. The present results are compared with these observations and recent theoretical ideas related to the CI events are discussed. It is proposed that CIs arise from intense bursts of cloud electrification and may follow the preexisting paths of cloud-to-ionosphere thunderstorm currents.

The spatial structure of an individual runaway breakdown pulse, stimulated

Revised model estimates of the effect of lightning on the lower

A one-dimensional, self-consistent computer code was used to predict

This paper reports on some propagation effects occurring while the

A numerical model called PICASSO [Production d'Ions Corona Au Sol Sous Orage

A simple quasi-two-dimensional model is used to study the zonal distribution

The possibility is considered of an avalanche-type increase of the number of

The artificially ionized layers in the atmosphere caused by microwave pulses

A chemical mechanism which reduces the electron concentration in the upper

Independent measurements of nitrogen oxides (NO/sub x/=NO+NO/sub 2/) were

In a rarefied plasma electron acceleration under the influence of an HF wave

High altitude optical transients-red sprites, blue jets, and elves-are modeled in the context of the relativistic electron runaway air breakdown mechanism. These emissions are usually with large mesoscale convective systems (hereafter MCS). In thunderstorms cloud electrification proceeds over time scale long enough to permit the conducting atmosphere above the cloud to polarize and short out the thunderstorm electric field. When a lightning strike rapidly neutralizes a cloud charge layer runaway driving fields can develop in the stratosphere and mesosphere. According to the authors' simulations of the full runaway process the variety of observed optical emissions are due to the nature of the normal lightning event in the MCS that kick starts the runaway avalanche. The authors describe some details of the model, present the results of the evolution of the primary electron population, and summarize the initial conditions necessary for different types of discharges. Two companion papers present: (a) the predicted optical, gamma ray, and radio emissions caused by these electrical discharges, and (b) the time evolution of the secondary electron population and its implications in terms of observables.

Recent years of observations of the upper atmosphere and the lower ionosphere brought a fascinating collection of new phenomena including optical, radio, and gamma-ray emissions originating in the 20 to 90 km altitude range. Up to now, the most diverse phenomenology has emerged from the optical observations which have led to the identification of red sprites, blue jets, blue starters and elves. Most of the previous studies have concentrated on relating such phenomena in the upper atmosphere to regular lightning discharges in the troposphere. For example, sprites and jets are believed to be optical manifestations of electrical discharges in the upper atmosphere caused by quasi-electrostatic fields penetrating to high altitudes during a regular lightning discharge. The sprite/jet discharge itself can be caused by the runaway air breakdown or regular air breakdown. The standard theory for optical airglow transients in the lower ionosphere above the thunderstorms also known as elves suggests that they are produced during interaction of electromagnetic pulses (EMP) from lightning with the lower ionosphere. Heating of the ambient electrons by the EMP in the D-region can result in excitation of optical emissions once the optical excitation thresholds are reached. In this paper the authors suggest that in addition to this mechanism elves can be caused by an EMP generated by sprites and jets. If sprites and jets are indeed accompanied by electrical discharges then some energy of their EMPs reaches to the ionosphere and heats ambient electrons there that in turn stimulates optical emissions similar to EMPs from regular lightning.

We use the runaway air breakdown model of upward discharges to calculate optical, radio, and X-ray radiation generated by red sprites.

Roussel-Dupre and Gurevich have developed a theory of gigantic atmospheric discharges directed upward from thundercloud tops into the Earth's stratosphere (1996). Formation of relativistic runaway electron avalanche initiated by cosmic-ray showers within the space domain of a thunderstorm electric field, is the heart of the theory. The theory allowed one to treat the origin of wide columns of light radiance observed repeatedly above thunderclouds. These light phenomena are known as

The discovery of electric discharges above thunderstorms has generated intense scientific interest. Studies of these `sprites' and `jets' have focused on their characterization by optical and radio techniques, with radar measurements of the causative storms providing insight into related weather. The authors describe a method for investigating the electric field structure above thunderstorms using ground-based radar to observe chaff dispersed by rockets. Slender conducting or dielectric chaff will generally align itself with the ambient electric field. This alignment is readily detected by appropriate configurations of polarimetric radar(s) such as are now used in meteorology to observe the nature and motion of hydrometeors. This is especially convenient as it permits the thunderstorms associated with sprites and jets to be characterized with the same experimental facility. This paper renders a preliminary examination of factors such experiments would entail and features that a multiparameter radar might utilize to probe chaff dispersed by small rockets. Monostatic and bistatic radar measurements of scatter from chaff provide a powerful tool to study electric fields associated with sprites and jets as well as other atmospheric electric fields.

Amplitude and phase perturbations on subionospheric VLF signals (known as