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Historically, the process of transient luminous event (TLE) detection has required an alert human observer on a low light level television (LLTV) monitor, either in real time or playback. The 1999 Sprites Balloon Campaign payloads had all-sky upward looking photometers not sensitive to events below the balloons. The photometer data was examined at the time of National Lightning Detection Network (NLDN) lightening strokes to find TLEs that were missed visually. 3602 events were analyzed in 4.1 h of storm time. Threshold current moments of ∼50 kA km for the positive cloud to ground (+CG) TLEs and ∼−5 kA km for negative cloud to ground (−CG) TLEs are found.

from a central excitation region directly above the storm. During the initial stages of the storm outwardly expanding waves possessed a period of � ≈10 min and wavelength � ≈50 km. Over a 1 h interval the waves gradually changed to longer period � ≈11 min and shorter wavelength � ≈40 km. Over the full 2 h observation time, about two dozen bright sprites generated by the underlying thunderstorm were recorded near the center of the outwardly radiating gravity wave pattern. No distinctive OH brightness signatures uniquely associated with the sprites were detected at the level of 2% of the ambient background brightness, establishing an associated upper limit of approximately A T . 0:5 K for a neutral temperature perturbation over the volume of the sprites. The corresponding total thermal energy deposited by the sprite is bounded by these measurements to be less than ∼1 GJ. This value is well above the total energy deposited into the medium by the sprite, estimated by several independent methods to be on the order of ∼1–10 MJ. c

Elves, halos and sprites were observed during August 1999 with a 1 ms high speed imager. The higher time resolution compared to conventional television cameras (17 or 20 ms ) allowed excellent images of the three phenomena temporally separate from each other to be obtained. Analysis of images of elves and halos indicates that the causal lightning-generated electromagnetic pulse and quasi-electro static fields are homogeneous and any small-scale (sub- 10 km ) structure, if visible, is most likely due to a structured atmosphere. Observations of sprites initiated to the side of a halo, without a halo, and from beads left over from a previous sprite, respectively, all suggest sub-pixel ( km ) background structures in atmospheric pressure or composition as being the dominant factors in determining the sprite “seed” location, or site of sprite initiation.

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 ∼16.7 ms integrated images, none of the sprites without a +CG had any discernible visual characteristic that would distinguish them from “regular positive sprites”. We have calculated the distribution of time intervals (Δt=tsprite−tlightning) for the sprites that had a parent +CG flash registered by the NLDN or VLF systems, and the distribution of distances between the sprite nadir positions and the flash locations registered by the NLDN. The time interval (Δt) distribution had a peak around 10– 20 ms and a mean of 30 ms (total). This distribution is broadly consistent with the characteristic single electron avalanche time scale associated with streamer growth between ∼70 and 85 km . The distribution of the distances (Δs) between the nadir point of sprites and the parent +CGs showed that approximately two-thirds of the sprites occurred within 50 km lateral displacement from the parent +CG. The parent +CG peak current distribution had a maximum at 40– 50 kA and mean of 60 kA , suggesting that high peak currents (I⩾75 kA ) are not a necessary prerequisite for sprites. The peak current distribution for all +CGs of the storm, with a maximum around 10– 20 kA and mean of 27 kA , exhibits a qualitatively different form from the peak current distribution of the parent +CGs producing sprites.

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 Π g − A 3 Σ 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-altitude spectrum is primarily 1PG but also shows the presence of features which appear to be N 2 + Meinel ( A 2 Π u − X 2 Σ g + ). The lower-altitude 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.

Flight 3 of the Sprites99 balloon campaign flew from 00:39:32 to 11:12:00 UTC on 21 August 1999, launched from Ottumwa, Iowa. Three axis electric and magnetic field and ground-based low light level TV observations from three sites were made of more than 68 transient luminous events (TLEs) in the middle atmosphere above thunderstorms in South Dakota and Kansas. At least four TLEs were recorded by two or more stations, including sprites at 0955:36, 0541:58 and 0546:10 UTC and a sprite halo at 0746:35. An event triggered on-board memory, sampling 10 quantities at a rate of 50 kHz per channel for 160 ms per event, recorded bursts for some of the sprites and elves. At the range of the balloon from the lightning and TLE (∼400 km), the vertical electric field perturbation is roughly simulataneous with the light emission. The presence of a radial component of some magnetic pulses suggests that signal propagation was not entirely in the TM mode.

Blue jets and blue starters are partially ionized luminous cones of primarily blue light that propagate upward out of the top of thunderstorms at speeds of order 100 km s−1. Blue jets propagate up ∼40 km, but blue starters, which resemble blue jets, terminate abruptly after only a few kilometers of upward travel. Theories on the origin of blue jets have proposed that they are due to either positive or negative streamers or runaway electrons. Quantitative analysis of new multi-instrument observations of a blue starter from an aircraft during the Energetics of Upper Atmospheric Excitation by Lightning, 1998 (EXL98) campaign of July 1998, shows that the ionization accounts for ∼3% of the observed intensity. Quantitative analysis of a remarkable color photograph of a blue jet taken from Reunion Island in the Indian Ocean shows that the minimum optical energy deposition was ∼0.5 MJ. The same photograph shows details of streamers never before seen.

Sprite halos were recently identified as an impulsive but spatially diffuse phenomenon that sometimes occurs just prior to, but distinct from, sprites. The lack of discernible spatial structure and the temporal development sequence in halos differs markedly from the highly structured bodies and tendrils and the complex development sequences of sprites. However, both phenomena are thought to result from an electric field due to charge moment changes usually associated with large positive cloud-to-ground (CG) lightning but also following negative CG flashes. Three-dimensional triangulations of sprites and sprite halos were made between stations in South Dakota and Wyoming in August 1999 during the NASA Sprites99 balloon campaign. Halos were found to have a Gaussian 1/e diameter of ∼66 km and 1/e thickness of ∼4 km. Comparison with the location of the underlying lightning strokes, as recorded by the National Lightning Detection Network (NLDN), confirms that the horizontal position of sprites may be laterally offset by as much as 50 km from the underlying parent lightning discharge, as has been previously reported. The point of maximum apparent brightness for sprite halos occurs at an altitude of ∼78 km, similar to that of sprites. However, unlike sprites, this point tends to be centered directly above the underlying parent lightning discharge, 4.6 ± 2.7 km mean distance from the center of the halo to the NLDN location. This difference in spatial location relative to the underlying lightning suggests that the electrical breakdown associated with discrete sprites may require a random ionizing event such as a micrometeor. In contrast, sprite halos do not appear to require such a random component.

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 we 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.

This paper reports observations of a distinctive form of sprites associated with positive CG flashes carrying currents of 23 or less to about 100 kA in mesoscale thunderstorms. The sprites are characterized by long vertical columns about 10 km long, less than 1 km in diameter, and show virtually no variation in brightness along their length. Three dimensional triangulation of what we define as a ‘columniform’ sprite (c-sprite) event on the evening of 19 June 1995 showed that the individual elements had an average terminal altitude of 86.7 km and an average bottom of 76.2 km. Some show faint diffuse ‘hair’ or tendrils extending above and below the column. The sprite columns are nearly vertical, in video imagery. On some evenings, c-sprites are the dominant form of sprite activity above thunderstorms but, on other nights with many sprites, they may not be observed at all. Comparison of c-sprite forms vs National Lightning Detection Network (NLDN) positive cloud-to-ground current, shows a progression from simple thin vertical forms to brighter and more complicated forms. Theoretical explanations which predict the form and vertical structure of the classical sprites do not at present account for these different forms.

Blue jets are narrow cones of blue light that appear to propagate upward from the cloud tops at speeds of about 100 km/s to terminal altitudes of about 40 km ( Wescott et al. 1995 ). In this paper, we present the results of a refined analysis of these optical phenomena and their relationship to cloud-to-ground (CG) and intracloud lightning, and to very large hailfall, their apparent color, and possible mechanisms for their production. In a thunderstorm where more than 50 of these events were observed from aircraft on the night of 1 July 1994, about half of the blue jets occurred in a cluster near Foreman, Arkansas, and the rest in an area near Texarkana, (Texas/Arkansas). Hail 7 cm in diameter fell in those two storm cells at the time of the blue jet occurrences. One other blue jet was observed over an intense multi cell storm in Kansas on the night of 3 July 1994. Comparison to cloud-to-ground (CG) lightning strokes revealed that blue jets were not coincident with either positive or negative CG strokes, but they occurred in the same general area as negative CG strokes and large hail, and that cumulative distributions of the negative CG strokes in ±5 s before and after the jet and within a radius of 15 km showed a significant reduction in the flash rate for 2 s following the event. From an analysis of color TV signal levels and calculations of quenching and atmospheric transmission, we conclude that significant ionization is present in the jets. Theoretical work by others suggests that the mechanism for their production is a streamer, but there remain discrepancies between these theories and the observations.

The results of a quasi-electrostatic electron heating model were combined with a time dependent N2 vibrational level population model to simulate the spectral distributions and absolute intensities observed in red sprites. The results include both N2 excited state vibrational level populations and time profiles of excited electronic state emission. Due to the long atmospheric paths associated with red sprite observations, atmospheric attenuation has a strong impact on the observed spectrum. We present model results showing the effect of atmospheric attenuation as a function of wavelength for various conditions relevant to sprite observations. In addition, our model results estimate the variation in the relative intensities of a number of specific N2 emissions in sprites (1PG, 2PG, and VK) in response to changes in observational geometry. A recent sprite spectrum, measured from the Wyoming Infrared Observatory (WIRO) on Jelm Mountain, during July, 1996, has been analyzed and includes N2 1PG bands down to v′ = 1. In addition to N2 1PG, our analysis of this spectrum indicates the presence of spectral features which are attributable to N+2 Meinel emission. However, due to the low intensity in the observed spectrum and experimental uncertainties, the presence of the N+2(A2Πu) should be considered preliminary. The importance of both the populations of the lower levels of the N2(B3Πg) and the N2(B3Πg)/N+2(A2Πg) population ratio in the diagnosis of the electron energies present in red sprites is discussed. While the current spectral analysis yields a vibrational distribution of the N2(B3Πg) which requires an average electron energy of only 1–2 eV, model results do indicate that the populations of the lower levels of the N2(B3Πg) will increase with increases in the electron energy primarily due to cascade. Considering the importance of the populations of the lower vibrational levels, we are beginning to analyze additional sprite spectra, measured at higher resolution, which contain further information on the population of B(v = 1).

On February 26, 1995, during a NASA sponsored mission to Peru to study red sprites and blue jets, the instrumented Westwind 2 jet aircraft encountered spectacular St. Elmo's fire from the wing pods, tail and nose while flying through a cloud at an altitude of 13.83 km (45,376 ft). The phenomenon was captured on low light level monochromatic and color television systems aboard the aircraft, and its spectrum was recorded on a low light level TV spectrograph with response from 395.0 to 750.0 nm. The cameras and spectrograph also recorded scattered intra-cloud lightning and a possible lightning discharge near, or to, the aircraft. The spectrum of St. Elmo's fire was primarily the second (2nd) positive bands of N2. The data were consistent with a population of electrons having relatively low energy (

We have determined the molecular internal energy distribution in the N 2 B 3 Π g state from the fluorescence measured during the observations of sprites during 1995. Spectrally resolved data from two different instruments and three different sprites are compared with theoretical spectra to obtain excited state vibrational distributions. Energy dependent electron excitation cross-sections and laboratory data were used to estimate the energies of electrons producing the red sprite radiance. Implications for chemical production in the mesosphere and critical future measurements are discussed.

Video images of the CRRES Gl, G9, and G1lA barium releases made at 400–500 km altitudes over the Caribbean in July 1991 have been analyzed to identify morphological features formed in the very early phases of the releases with the aim of associating specific physical processes with these features. Three features are presented: the observation that the inner edge of the ion cloud is located some distance from the release point along the orbital track (“skidding”); the formation of an elongated striation at the inner edge of the ion cloud and an ion depleted region behind the striation; and the formation of a flat neutral barium disk perpendicular to the magnetic field B that is centered some tens of kilometers from the release point. We are linking these morphological features with effects associated with the polarization of the initially dense ion cloud created by solar UV illumination. A simple physical model of the release and the polarization process is presented. Model predictions are both qualitatively and quantitatively in good agreement with the observations. The skidding distance appears to be controlled by the background ionospheric density and the size of the release; the structure in the early ion cloud is due to electric fields primarily setup and maintained by the polarization of the densest part of the ion cloud; and the neutral disk is formed by charge exchange between counterstreaming ions and neutrals outside the polarized core. For the three releases analyzed, no additional internal plasma processes nor processes coupling the release to the ionosphere appear to be critical for the formation of the observed features in the initial ion cloud.

This paper documents the first observations of a new stratospheric electrical phenomenon associated with thunderstorms. On the night of 30 June (UT 1 July) 1994, 30 examples of these events, which we have called “blue starters,” were observed in a 6 m 44 s interval above the very energetic Arkansas thunderstorm where blue jets were first observed. The blue starters are distinguished from blue jets by a much lower terminal altitude. They are bright and blue in color, and protrude upward from the cloud top (17–18 km) to a maximum 25.5 km (83,655 ft.) in altitude. All blue starters events were recorded from two small areas near Texarkana, Texas/Arkansas where hail 7.0 cm in diameter was falling. Comparison to cloud-to-ground (CG) lightning flashes revealed: 1. Blue starters were not observed to be coincident with either positive or negative CG flashes, but they do occur in the same general area as negative CG flashes; 2. Cumulative distributions of the negative CG flashes in ±5 s before and after the starter and within a radius of 50 km shows a significant reduction for about 3 s following the event in the two cells where starters and jets were observed. The energy deficit is approximately 109 J. It is possible that blue starters are a short-lived streamer phenomenon.

A TV slit spectrograph was used to obtain the first optical spectra of sprites. Twenty-five events were observed over a thunderstorm on the border of Nebraska and Colorado on the night of 22 June, 1995 between 0700 and 0900 UT. For 10 of these events optical spectra were measured in the wavelength range from 540 to 840 nm. After correcting for the spectrograph response function, digitized spectrograph video images are used to measure the wavelengths of and ratios between the emissions. All emissions are found to be of the first positive bands of N2. There is no evidence of the Meinel bands of N2+ indicating that the mechanism responsible for sprites produces little or no ionization at 70 km altitude.

An experimental campaign designed to study high-latitude auroral arcs was conducted in Sondre Stromfjord, Greenland, on February 26, 1987. The Polar Acceleration Regions and Convection Study (Polar ARCS) consisted of a coordinated set of ground-based, airborne, and sounding rocket measurements of a weak, sun-aligned arc system within the duskside polar cap. A rocket-borne barium release experiment, two DMSP satellite overflights, all-sky photography, and incoherent scatter radar measurements provided information on the large-scale plasma convection over the polar cap region while a second rocket instrumented with a DC magnetometer, Langmuir and electric field probes, and an electron spectrometer provided measurements of small-scale electrodynamics. The large-scale data indicate that small, sun-aligned precipitation events formed within a region of antisunward convection between the duskside auroral oval and a large sun-aligned arc further poleward. This convection signature, used to assess the relationship of the sun-aligned arc to the large-scale magnetospheric configuration, is found to be consistent with either a model in which the arc formed on open field lines on the dusk side of a bifurcated polar cap or on closed field lines threading an expanded low-latitude boundary layer, but not a model in which the polar cap arc field lines map to an expanded plasma sheet. The antisunward convection signature may also be explained by a model in which the polar cap arc formed on long field lines recently reconnected through a highly skewed plasma sheet. The small-scale measurements indicate the rocket passed through three narrow (less than 20 km) regions of low-energy (less than 100 eV) electron precipitation in which the electric and magnetic field perturbations were well correlated. These precipitation events are shown to be associated with regions of downward Poynting flux and small-scale upward and downward field-aligned currents of 1-2 micro-A/sq m. The paired field-aligned currents are associated with velocity shears (higher and lower speed streams) embedded in the region of antisunward flow.

VLF perturbations on signals propagating along great-circle-paths (GCP) through electrically active midwest thunderstorms are associated with luminous high altitude glows (referred to as sprites) observed from aircraft or ground. The data constitutes the first evidence that the physical processes leading to sprites also alter the conductivity of the lower ionosphere.

The dual jet aircraft Sprites94 campaign yielded the first color imagery and unambiguously triangulated physical dimensions and heights of upper atmospheric optical emissions associated with thunderstorm systems. Low light level television images, in both color and in black and white (B/W), obtained during the campaign show that there are at least two distinctively different types of optical emissions spanning part or all of the distance between the anvil tops and the ionosphere. The first of these emissions, dubbed 'sprites' after their elusive nature, are luminous structures of brief (less than 16 ms) duration with a red main body that typically spans the latitude range 50-90 km, and possessing lateral dimensions of 5-30 km. Faint bluish tendrils often extend downward from the main body of sprites, occasionally appearing to reach cloud tops near 20 km. In this paper the principal characteristics of red sprites as observed during the Sprites94 campaign are described. The second distinctive type of emissions, 'blue jets,' are described in a companion paper (Wescott et al., this issue).

Short-duration upper atmospheric optical flashes were recorded on the night of 8 July, 1993 (9 July UT) from the NASA DC-8 Airborne Laboratory flying over the American Midwest. All-sky video images from an intensified silicon intensified target (ISIT) camera revealed 19 upper atmospheric flashes occurring over a period of approximately 100 min. The flashes were similar in appearance to previously reported ground and shuttle-based video observations. Detailed analysis of 12 of the events yielded these parameters: (1) duration less than or equal to 17 ms; (2) brightness 10-50 kR, roughly that of bright aurorae; (3) terminal heights 30-100 km, with a mean of approximately 60 km; (4) horizontal extent 10-50 km; (5) emission volumes greater than 1000 cu km. The relative frequency of the optical flashes was (6) 1:200-1:400 compared to negative cloud-to-ground discharges and 1:20-1:40 compared to positive cloud-to-ground discharges.

On two evenings in 1968, anomalous field-aligned brightenings or emission enhancements of up to 3X were observed to move rapidly through three different Ba(+) clouds over Andoya, Norway. Similar effects were observed in Ba(+) clouds released from rockets launched from Poker Flat, Alaska, on March 21, 1973 and on March 22, 1980. On these occasions, auroras on or near the Ba(+) L shell also exhibited active rapid ray motions, which prompts the assumption that the two phenomena are related and the expectation that an explanation of the rapid ray motions in the Ba(+) clouds would lead to a better understanding of the physics of auroral ray motions and the auroral atmosphere. Seven possible mechanisms to produce the observed moving emission enhancements are discussed. The observations provide strong evidence for the existence of transient electric fields of order 100 mV/m at altitudes as low as 200 km during active aurora with rapid ray motions.

[1] A near-ultraviolet (NUV) spectrograph (320–460 nm) was flown on the EXL98 aircraft sprite observation campaign during July 1998. In this wavelength range video rate (60 fields/sec) spectrographic observations found the NUV and blue emissions to be predominantly N2 (2PG). The negligible level of N2+ (1NG) present in the spectrum is confirmed by observations of a co-aligned, narrowly filtered 427.8 nm imager and is in agreement with previous ground-based filtered photometer observations. The synthetic spectral fit to the observations indicates a characteristic energy of ∼1.8 eV, in agreement with our other NUV observations.

A rocket borne Critical Ionization Velocity (CIV0 experiment was carried out from Wallops Island at dusk on May 4, 1989. Two barium shaped charges were released below the solar terminator (to prevent photoionization) at altitudes near 400 km. The ambient ionospheric electron density was 50,000/cu cm. The neutral barium jet was directed upward and at an angle of nominally 45 degrees to B which gives approximately 3 x 10 to the 23rd neutrals with super critical velocity. Ions created by a CIV process in the region of the neutral jet would travel up along B into sunlight where they can be detected optically. Well defined ion clouds (max. brightness 750 R) were observed in both releases. An ionization rate of 0.8 percent/sec (125 sec ionization time constant) can account for the observed ion cloud near the release field line, but the ionization rate falls off with increasing distance from the release. It is concluded that a CIV process was present in the neutral jet out to about 50 km from the release, which is significantly further than allowed by current theories.

[1] On 25 March 2003, Horizontal E-Region Experiment (HEX) released trimethyl aluminum trails from two rockets launched northward from Poker Flat Research Range near Fairbanks to map the vertical wind field near a stable premidnight auroral arc system. They deployed three trails of trimethyl aluminum chemical “puffs,” whose subsequent motion traced the prevailing wind field. This motion was determined using triangulation from four ground observation sites. Position and speed accuracies were estimated to be ∼1 km and a few meters per second, respectively. The first rocket followed a novel flat trajectory; it released a nearly horizontal trail of length 200 km, at an average altitude of ∼145 km. The second rocket was launched 19 min later and released two trails between 125 and 175 km altitude along a conventional steep trajectory. All puffs between 130 and 175 km altitude drifted geomagnetic westward, almost exactly parallel to the aurora. From prior observations and modeling, we had expected to observe convective upwelling near the arcs. We did not; vertical winds were essentially downward throughout the horizontal trail, with speeds between 0 and 20 m s−1. Although an abatement of downward flow was observed ∼40 km equatorward of the arcs, these data alone do not establish a causal relationship between the abatement and the arcs. Vertical speeds of ≤20 m s−1 are relatively modest. However, because the observed wind field would entrain air parcels in flow parallel to the arc system, even vertical speeds around 15 m s−1 could displace individual air parcels by several scale heights if they occurred all along the arcs.

[1] A balloon campaign was conducted in summer, 1999, to measure the stratospheric electromagnetic fields associated with sprites. Ground observations for detection of sprites included low light level TV (LLTV) observations from three sites. Flight 1 flew from Palestine, Texas at 01:14:31 UTC to 09:45:00 UTC on 07/06/1999. Flight 3 of the campaign flew from Ottumwa, Iowa at 00:39:32 UTC to 11:12:00 UTC on 08/21/99. During flight 3, 26 sprite halos associated with positive cloud-to-ground (+CG) strokes and 17 −CG sprite halos were observed. Of these, 22 +CG and 12 −CG sprite halos were observed by the ground observatories. Seven of the +CG and all 17 −CG halos were not followed by sprites. Next the balloon data were examined during and after the times of the recorded NLDN strokes during 4.1 hours of data. An additional 88 −CG TLEs were found in the flight 3 data and 56 TLEs (7 +CG, 49 −CG) were found in the flight 1 data. It appears that −CG TLEs, mostly spriteless halos, occurred 5–7 times more often than the +CG TLEs. The halo appears to be a fundamental mesospheric response to lightning.

The electrical resistivity of the ground can be measured by several methods. One, which has proven useful, is the controlled source magnetotelluric method (CSAMT). Current over a wide range of frequencies is introduced into the earth through a grounded dipole. Then the resulting electric and magnetic fields are measured at a distance greater than several skin depths. The apparent resistivity is then calculated by: p = 1/5f E/B(exp 2) The apparent resistivity vs. frequency can be converted into true resistivity vs. depth, This grant involved an investigation into the HAARP virtual antenna pattern out to 200 km, and its use as a CSAMT transmitter.

Recent observations of the effects of lightning on the middle and upper atmosphere have revealed several new dynamical effects of sprites and yielded initial estimates of the total internal energy, including energy residing in nonradiative vibrational states. High speed images (1000 fps) of sprite development and decay show evidence of modification of the local atmosphere by sprites, which may in turn affect the form of subsequent sprites occurring in the same region. Small, relatively long lived (∼100s ms) statinary “balls” are often observed within the decaying regions of some sprite tendrils. Calculations of diffusion time scales for the balls are roughly consistent with thermal diffusion, but the relatively long lifetime of the balls relative to nearby tendrils suggests that other processes, perhaps chemical in nature, are operative to extend the lifetime of the balls. Other contrasting features within sprites include an invariably spatially diffuse top and highly structured tendril bottoms. Following the suggestion of Williams [2000], we test as a possibly useful plasma parameter the number of electrons per electron-neutral collision volume for being potentially able to account for the clear separation between the highly structured tendril lower region and the diffuse upper regions of sprites. Models of spectrographic measurements of sprites obtained in 1998 sugges that substantial energy resides in nonradiating vibrational states of both molecular nitrogen and oxygen, in addition to the energy associated with the N2(1PG) optical emissions. Estimates of the internal energy of sprites are ∼1 GJ for a large event.

This project comprises five separate elements that address science and education objectives of the HAARP program. These elements are: (1) To establish the characteristics of the ionospheric source region responsible for the ELF/VLF waves generated by modulation of HAARP HF emissions, and to measure the ELF radiation pattern. (2) To attempt to stimulate hydromagnetic waves in the onospheric waveguide using the HAARP heater. (3) To develop a simulation model for the plasma physical and electromagnetic ffects of localized ionospheric heating with the purpose of predicting outcomes of heating experiments and to guide the design of ew experiments. (4) Using the SuperDARN instrument on Kodiak, to examine the formation of ionospheric irregularities within the heated volume and the relationship of the irregularities to other observations such as the generation of Stimulated Electromagnetic missions. (5) To provide scientific education about HAARP and physical science in general to members of the local Copper Valley ommunity. In this report the results of research obtained to date in each of the five program elements are reviewed, and ecommendations for follow up activities are presented.

The ACTIVNY satellite launched on Sept. 30, 1989 was a platform for a suite of active plasma experiments, including releases of Xe gas to test Alfven's critical velocity effect. Three releases were done over Alaska and three over Utah, all fully illuminated by sunlight. We attempted optical observations from ground stations in the dark, using various low light level imagers and spectrographs, with narrow bandpass filters on XeI and XeII lines and also in white light. Viewing conditions were very good on several releases, the satellite could tracked easily, but we saw no optical evidence of the releases from any wavelength. We discuss the reasons why optical diagnostics in the visible and near infrared failed to detect emissions from the releases.

Sprites, blue jets, blue starters, and elves are recently documented optical evidence of previously unknown forms of upward electrical energy transport across the stratopause. These energetic processes have not been incorporated into most models or descriptions of middle- and upper-atmospheric dynamics, in part because the details of the processes themselves are still poorly understood. The earliest (1995) ground based red spectral observations of neutral molecular nitrogen emissions from sprites indicate a low energy phenomena compared to the neutral and ionized emissions observed in lightning or aurora. However, recent sprite observations of ionized molecular nitrogen emissions indicate the presence of higher energy processes. In 1998, the EXL98 aircraft campaign characterized the blue emissions of sprites, blue jets, and elves. Aircraft measurements include filtered images, at 427.8 nm (N + 2 (1NG)) and 340.7 nm (N 2 (2PG)), as well as NUV/blue spectral observations between 320-460 nm, while ground based time-resolved photometric measurements were also made in this wavelength range. We discuss the filtered and spectral NUV observations in conjunction with earlier red (640-920 nm) spectral and filtered photometer observations. The identification of ionized nitrogen emissions indicates processes with electron energies of at least 18.6 eV to produce these emissions, assuming excitation is directly from the N 2 ground state. This paper provides middle- and upper-atmospheric scientists an introduction to these recently discovered phenomena and the current best estimates of the energetic contributions of these phenomena to the atmosphere above the tropopause.

[1] During the EXL98 aircraft mission, sprites and blue jets were observed by narrow band cameras that measure the N2+ 1NG (0,1) band at 4278A and the N2 2PG (0,0) band at 3370A. We discuss the observations (∼1km 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 55km. Characteristic electron energies (ECh) 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 (Ek) and ECh is ∼2.2eV. Above 55km E drops below Ek and ECh drops to ∼1.75eV near 60km.

[1] 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 ∼105 to ≥3 × 107 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.

[1] A balloon campaign was conducted in summer, 1999, to measure the stratospheric electromagnetic fields associated with sprites. The balloon payloads were instrumented with electric field detectors, magnetometers, an upward looking photometer, and other instruments. Ground observations for detection of sprites included low light level TV (LLTV) observations from three sites, Jelm Mt., Wyoming, Bear Mt., South Dakota, and Yucca Ridge, Colorado. Flight 3 of the campaign flew from Ottumwa, Iowa at 00:39:32 UTC to 11:12:00 UTC on 08/21/99. A sprite at 0955:36.980 UTC produced a vertical electric field perturbation of ∼0.275 V/m that was similar in time profile to the light emission. There was also a positive azimuthal magnetic pulse of ∼3 nT.

As part of the NASA Combined Release and Radiation Effects Satellite (CRRES) chemical release program in September 1990, two Ba and also one each Sr and Ca canisters of a boron-titanium thermite mixture, which vaporizes the element on ignition, were released near perigee after dusk in the South Pacific to study the critical velocity effect proposed by Alfven. The critical velocities of these three elements are 2.7, 3.5, and 5.4 km/s respectively, all well below the orbital velocity of 9.4 km/s. On September 10, 1990, a Sr and Ba pair (G-13, or critical ionization velocity (CIV) I) was released near Rarotonga at approximately 515 km altitude in a background electron density of 3.4 x 10(exp 6)/cu cm. On September 14, 1990, G-14 or CIV II released a Ca and Ba pair west of New Caledonia near 595 km at an electron density of 1.5 x 10(exp 6)/cu cm. Ions of all three elements were observed with low-light level imagers from two aircraft after they had transited up the magnetic field lines into the sunlight. Emissions from the spherically expanding neutral gas shells below the solar terminator, observed with cameras filtered for the Ba(+) ion line at 4554 A and also in unfiltered imagers for approximately 15 s after release, are probably due to excitation by hot electrons created in the CIV process. The ions created clearly lost much of their energy, which we now show can be explained by elastic collisions: Ba(+) + O. Inventories of the observed ions indicate yields of 0.15% and 1.84% for Ba in the first and second experiments, 0.02% for Sr and 0.27% for Ca. Ionization from all the releases continued along the satellite trajectory much longer (greater than 45 s) than expected for a CIV process. The ion production along the satellite track versus time typically shows a rapid rise to a peak in a few seconds followed by an exponential decrease to a level essentially constant rate. The characteristic distances for CIV I and II are 47 and 62 km, respectively. We interpret the early time rise and exponential fall to be due to CIV ionization, of 0.014% (CIV I) and 0.40% (CIV II) for the Ba releases. The later ions produced at a constant rate probably have origins from other such processes as stripping and associative ionization collisions with atmospheric constituents primarily O, and charge exchange with O(+), He(+), and H(+). We suggest that the much larger Ba ionization rate in CIV II than CIV I is due to the fact that the release occurred in the peak Ca density where hot electrons were already present.

The barium releases from the CRRES satellite have provided an opportunity for verifying theoretically calculated barium ion and neutral emission rates. Spectra of the five Caribbean releases in the summer of 1991 were taken with a spectrograph on board a U.S. Air Force jet aircraft. Because the line of sight release densities are not known, only relative rates could be obtained. The observed relative rates agree well with the theoretically calculated rates and, together with other observations, confirm the earlier detailed theoretical emission rates. The calculated emission rates can thus with good accuracy be used with photometric observations. It has been postulated that charge exchange between neutral barium and oxygen ions represents a significant source for ionization. If so. it should be associated with emissions at 4957.15 A and 5013.00 A, but these emissions were not detected.

The quasi-dc electric fields measured in the CRIT I ionospheric release experiment are studied. In the experiment, two identical barium shaped charges were fired toward a main payload, and three-dimensional measurements of the electric field inside the streams were made. The relevance of proposed mechanisms for electron heating in the critical ionization velocity (CIV) mechanism is addressed. It is concluded that both the 'homogeneous' and the 'ionizing front' models probably are valid, but in different parts of the streams. It is also possible that electrons are directly accelerated by a magnetic field-aligned component of the electric field. The coupling between the ambient ionosphere and the ionized barium stream is more complicated that is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes.

In May 1986 an experiment was performed to test Alfven's critical ionization velocity (CIV) effect in free space, using the first high explosive shaped charge with a conical liner of strontium metal. The release, made at 540 km altitude at dawn twilight, was aimed at 48 deg to B. The background electron density was 1.5 x 10(exp 4) cu cm. A faint field-aligned Sr(+) ion streak with tip velocity of 2.6 km/s was observed from two optical sites. Using two calibration methods, it was calculated that between 4.5 x 10(exp 20) and 2 x 10(exp 21) ions were visible. An ionization time constant of 1920 s was calculated for Sr from the solar UV spectrum and ionization cross section which combined with a computer simulation of the injection predicts 1.7 x 10(exp 21) solar UV ions in the low-velocity part of the ion streak. Thus all the observed ions are from solar UV ionization of the slow (less than critical) velocity portion of the neutral jet. The observed neutral Sr velocity distribution and computer simulations indicate that 2 x 10(exp 21) solar UV ions would have been created from the fast (greater than critical) part of the jet. They would have been more diffuse, and were not observed. Using this fact it was estimated that any CIV ions created were less than 10(exp 21). It was concluded that future Sr CIV free space experiments should be conducted below the UV shadow height and in much larger background plasma density.

A critical velocity ionization experiment was carried out with a heavily instrumented rocket launched from Wallops Island on May 13, 1986. Two neutral barium beams were created by explosive shaped charges released from the rocket and detonated at 48 deg to B at altitudes near 400 km and below the solar UV cutoff. Critical velocity ionization was expected to form a detectable ion jet along the release field line, but, instead, an ion cloud of fairly uniform intensity was observed stretching from the release field line across to where the neutral barium jet reached sunlight. The process creating these ions must have been present from the time of the release; the efficiency is estimated to be equivalent to an ionization time constant of 1800 sec. This ionization is most likely from collisions between the neutral barium jet and the ambient atmospheric oxygen, and, if so, the cross section for collisional ionization is 9 x 10 to the -18th sq cm.

Two barium-plasma injection experiments were carried out during magnetically active periods in conjunction with the Skylab 3 mission. The high-explosive shaped charges were launched near dawn on November 27 and December 4, 1973, UT. In both cases, the AE index was near 400 gammas, and extensive pulsating auroras covered the sky. The first experiment, Skylab Alpha, occurred in the waning phase of a 1000-gamma substorm, and the second, Skylab Beta, occurred in the expansive phase of an 800-gamma substorm. In both, the convection was generally magnetically eastward, with 100-km-level electric fields near 40 mV/m. However, in the Alpha experiment the observed orientation of the barium flux tube fit theoretical field lines having no parallel current, but the Beta flux-tube orientation indicated a substantial upward parallel sheet current.

On 16 March 1980 a rocket launched from Poker Flat, Alaska, carried a new type of high-explosive barium shaped charge to 571 km, where detonation injected a thin disk of barium vapor with high velocity nearly perpendicular to the magnetic field. The purpose of the experiment, named “King Crab,” was to advance knowledge of the instabilities, waves, and optical and magnetic effects produced. The TV images of the injection are spectacular, revealing three major regimes of expanding material which showed early instabilities in the neutral gas. The most unusual effect of the injection is a peculiar rayed barium-ion structure lying in the injection plane and centered on a 5 km “black hole” surrounding the injection point. Preliminary computer simulations show a similar rayed structure development due to an electrostatic instability.

Television observations of a barium-plasma flux tube extending from near 4500 km to near 10,000 km during a magnetic substorm and dawn-sector auroral display indicated several interesting anomalous events. Beyond 5500 km, there was a rapid increase in brightness accompanied by flux-tube splitting and diffusion, leaving behind a truncated single flux tube. From the orientation of the flux tube compared with theoretical field models, the presence of a substantial field-aligned current sheet is deduced. A suggested explanation of these phenomena is given in terms of a plasma potential double layer.

Two rocket experiments, performed in January 1975, investigated convection of plasma formed by solar photoionization of barium injected into the northern magnetospheric cleft at 13 km/s upward and parallel to the local geomagnetic field. Plasma convection was demonstrated from the cleft's poleward region, directly into and across the polar cap, and possibly into the convection system of the nightside auroral electrojet; plasma injected centrally within the cleft under quiet magnetic conditions remained in the cleft convection system for at least 22 min and revealed a highly structured E-field over about 600 km of longitudinal extent. Cleft location agreed with that predicted by ionosondes.

A rocket launched from Poker Flat, Alaska, carried a new type of high-explosive barium shaped charge to 571 km, where detonation injected a thin disk of barium vapor with high velocity nearly perpendicular to the magnetic field. The TV images of the injection are spectacular, revealing three major regimes of expanding plasma which showed early instabilities in the neutral gas. The most unusual effect of the injection is a peculiar rayed barium-ion structure lying in the injection plane and centered on a 5 km 'black hole' surrounding the injection point. Preliminary electrostatic computer simulations show a similar rayed development.

Telluric currents have been recorded for several months at the geomagnetically conjugate points, Cold Bay in the Aleutian Islands and Oamaru in New Zealand. It was found that major disturbances occur simultaneously, have the same duration, and usually show peak-for-peak correspondence at the two stations. Other Alaskan stations (College, Pt. Barrow) generally experience the same disturbances but the detailed variations fail to correlate with Oamaru. Disturbances at Cold Bay and Oamaru show elliptical polarization, with opposite directions in the two hemispheres. The amplitude of short period (about 1 min) fluctuations relative to longer periods (about 10 min) is greater at Oamaru than Cold Bay, probably owing to differing electrical conductivities at the two sites.

Electric field variations in vicinity of auroral forms from motions of Ba vapor clouds released from Nike-Tomahawk rockets

Polar cap electric field measurements, and model for Hall current auroral electrojet continuity and polar cap magnetic disturbances

IGY magnetograms from eleven stations in Alaska and Siberia were compared with Macquarie Island records for correlation. The conjugate area defined by contours of equal correlation coefficient varies in size, shape, and location with time, but is generally elongated along a line of constant L value. Some definite departures from conjugacy were found and are discussed. No pronounced daily or seasonal change was found in form correlation between Macquarie Island and Kotzebue. The relative size of afternoon and early evening disturbances definitely varies with season, probably as a result of seasonal changes of ionospheric conductivity. The coherence of magnetic disturbances was investigated using Alaska net magnetograms, since this affects the size and shape of a conjugate area. Tight coherence was always noted in a group of stations spread 350 km east-west and 125 km north-south.

Transient variations in the earth's magnetic field may be expected to induce electric current concentrations along the ocean-land boundary. Depending upon the direction of the inducing field, magnetic effects in the vertical and horizontal component normal to the coast are predicted. The electric component will tend to be polarized perpendicular to the shore on land and parallel offshore. This paper presents the results of magnetic and telluric current measurements on both sides of the coast near Barrow, Alaska. Owing to the gradually shelving water depth, and the low (10 Ω m) resistivity of the land, no magnetic coast effect of greater than a few per cent was found. There is a polarization at nearly all sites in E nearly perpendicular to the coast including a site 3 km offshore. The frequency response of telluric current variations is relatively low to disturbances of the order of 10-second period.