OBSERVATIONS OF SPRITES, BLUE JETS, AND ELVES IN THE MID-WEST USING GROUND-BASED VIDEO EQUIPMENT by Paul J. McCrone ATS 797 Directed Independent Research Prof. : Dr. Dean Morss Date : 20 November 1996 Creighton University Dept. of Atmospheric Sciences Omaha NE Paul J. McCrone ATS 797 20 November 1996 Dr. Morss OUTLINE TITLE: "OBSERVATIONS OF SPRITES, BLUE JETS, AND ELVES IN THE MID-WEST USING GROUND-BASED VIDEO EQUIPMENT" ABSTRACT I. INTRODUCTION A. What Are "Sprites", "Blue Jets", and "Elves"? 1. General Description a) Sprites b) Blue Jets c) Elves 2. Past Observations/History of Sprites in Science 3. Current Theories / Hypotheses a) Wilson's Thunderstorm Electric Field Theory b) Rousell-Dupre' c) Meteorites d) Others B. Why Study Cloud -to- Ionosphere events? 1. Possible Impacts on Chemistry of Upper Atmosphere 2. Impact on High Altitude Aircraft and Spacecraft 3. Insight into electrical charge distribution / interaction in the Atmosphere C. Current Observation Efforts 1. Video a) Ground based observations b) Aircraft measurements c) Spacecraft imagery 2. VLF detection II. OBSERVATION EFFORTS AT CREIGHTON UNIVERSITY A. Equipment used B. Method of Employment C. Results 1. Multiple events from August 15, 1996 a) Synoptic Weather Scenario b) Location / Description of local conditions c) Imagery / Information 2. Events from August 22, 1996 a) Synoptic Weather Scenario b) Location / Description of local conditions c) Imagery / Information 3. Miscellaneous III. LESSONS LEARNED / AREAS FOR FUTURE IMPROVEMENT A. Multispectral Data 1. Conventional visual data 2. Low-light Video 3. Multi-filter imagery 4. Image analysis B. Utility of Digital Radar data and NLDN information C. VLF data correlation D. Additional resources needed 1. Personnel 2. Power supply 3. Location and number of Observation Sites IV. CONCLUSIONS APPENDIX A: Calculation of Sprite Altitude APPENDIX B: Calculation of Electrical Field associated with Sprites BIBLIOGRAPHY ABSTRACT During the summer months of 1996, efforts at Creighton University have been directed towards searching for a little-understood phenomenon in the upper atmosphere. Referred to as "Red Sprites", "Blue Jets" and "Elves", these events are characterized by the emission of reddish/orange, blue, and green light between the top of thunderstorm clouds and the ionosphere. Believed to be somewhat similar to the Aurora Borealis, these lights in the sky are caused by the near visible emission of high energy electrons and other ions colliding/interacting with gaseous species in the stratosphere and mesosphere. The primary focus of this effort has been to obtain as much information as possible regarding these events, with an emphasis toward collection of actual sprite imagery / data, in order to best increase our understanding of these phenomena. In addition, our intention was to determine the most effective and meaningful way in which to gather data, and observe these events. Included are descriptions of actual Sprite and Elve occurrences during July through August 1996. I. INTRODUCTION A. What Are "Sprites", "Blue Jets", and "Elves"? Sprites, Blue Jets, and Elves are all different categories of electromagnetic emissions occurring in the region between the ionosphere and the tops of cumulonimbus clouds (or any other kind of lightning - producing clouds). For the sake of simplicity, these events will be referred to with a shortened term : "C-I event" (Cloud - to - Ionosphere event). The term "Cloud - to - Ionosphere" is not meant to imply that the emission starts at the cloud, then ends in the ionosphere. This issue is still unresolved. Here, a brief description of each of the C-I events will be provided, including a review of past observations 1. General Description a) Sprites The term "Sprite" is actually an acronym, as follows [Jeong, 1996]: S - Stratospheric / Mesospheric P - Perturbations R - Resulting from I - Intense T - Thunderstorm E - Electricification The following summary provides the best overview of sprites available: "Sprites are massive but weak luminous flashes that appear directly above an active thunderstorm system and are coincident with cloud-to-ground or intracloud lightning strokes. Their spatial structures range from small single or multiple vertically elongated spots, to spots with faint extrusions above and below, to bright groupings which extend from the cloud tops to altitudes up to about 95 km. Sprites are predominantly red. The brightest region lies in the altitude range 65- 75 km, above which there is often a faint red glow or wispy structure that extends to about 90 km. Below the bright red region, blue tendril-like filamentary structures often extend downward to as low as 40 km. Sprites rarely appear singly, usually occurring in clusters of two, three or more. Some of the very large events, ......... seem to be tightly packed clusters of many individual sprites. Other events are more loosely packed and may extend across horizontal distances of 50 km or more and occupy atmospheric volumes in excess of 10,000 cubic km. " "High speed photometer measurements show that the duration of sprites is only a few ms. Current evidence strongly suggests that sprites preferentially occur in decaying portions of thunderstorms and are correlated with large positive cloud-to-ground lightning strokes. The optical intensity of sprite clusters, estimated by comparison with tabulated stellar intensities, is comparable to a moderately bright auroral arc. The optical energy is roughly 10-50 kJ per event, with a corresponding optical power of 5-25 MW. Assuming that optical energy constitutes 1/1000 of the total for the event, the energy and power are on the order of 10-100 MJ and 5-50 GW, respectively." "If sprites are only barely detectable by the unaided human eye, in intensified television images obtained from the ground and from aircraft they appear as dazzlingly complex structures that assume a variety of forms." [Heavner, 1995] Typically, sprites have structures known as a "head" (the brightest part, colored red), "hair" (a fainter, reddish glow above the head), and faint bluish / purple tendrils that extend downward [Sentman et all, 1995]. See figure 1 for an example of a typical sprite [example provided by Heavner, 1996]. Sprites also have a clear, distinctive Very Low Frequency (VLF) signature, making them detectable even during daylight hours. From the beginning of modern C-I research in 1990, many have compared the reddish colors and hues of a sprite are reminiscent of the aurora. This suggested "...that the light of a sprite, like that of the aurora, comes from oxygen or nitrogen molecules excited by collisions with high energy electrons" [Kerr, 1995] b) Blue Jets The following discussion provides the best description of Blue Jets: "Blue jets are a second high altitude optical phenomenon, distinct from sprites, observed above thunderstorms using low light television systems. As their name implies, blue jets are optical ejections from the top of the electrically active core regions of thunderstorms. Following their emergence from the top of the thundercloud, they typically propagate upward in narrow cones of about 15 degrees full width at vertical speeds of roughly 100 km/s (Mach 300), fanning out and disappearing at heights of about 40-50 km. Their intensities are on the order of 800 kR near the base, decreasing to about 10 kR near the upper terminus. These correspond to an estimated optical energy of about 4 kJ, a total energy of about 30 MJ, and an energy density on the order of a few mJ/m3. Blue jets are not aligned with the local magnetic field." [Heavner, 1995] As the name implies, the appearance of these C-I events is normally blue. The average duration of the apparent source of a blue jet is roughly 200 ms. The entire event lasts about 200-300 ms, total. Often, they are observed to follow upward lightning strokes. c) Elves The term "Elves" is also an acronym, as follows [Jeong, 1996]: E - Emissions of L - Light and V - VLF Perturbations from E - EMP (Electromagnetic Pulse) S - EventS This category of C-I event is a relatively new variety. Lyons et al [1996] described elves as "brief (~ 1ms) brightenings of the airglow layer ... as a distinct phenomenon" and as an "amorphous glowing region". Observers have noted a greenish hue with these events. Others have described elves as follows "Elves are bright but diffuse luminous disks at altitudes of 80-100 km formed 300 (microseconds) after the initiating cloud-ground (CG) lightning and lasting only about 1 ms." [Dowden et al, 1995]. Like sprites, elves have an identifiable VLF signature. As implied by the acronym, current theories on elve generation are focused around the Electromagnetic Pulse (EMP) from lightning discharges below. 2. Past Observations/History of Sprites in Science It may seem that these "vertical lightning displays" are a new observed phenomena. In reality, numerous reports have been given in the past regarding these events. One of the first known records of a C-I event was by Mackenzie [1886], when a series of sprites, blue jets and possibly elves were observed by seamen near Jamaica. C.T.R. Wilson [1956] reported observing such a display in his remarkable paper on Atmospheric Electricity. Vonnegut [1980] also reported such emissions. Numerous reports of these "strange lightning" events are described by the many eye-witnesses documented in the work of Corliss [1982]. The accounts in Corliss' works may contain many numerous examples if C-I events, since the whole idea of sprites was not widely known up to that time. Many good examples of C-I events are likely misclassified as either "Rocket Lightning" or "Auroras correlated with Thunderstorms". Another account of "lightning to the ionosphere" was given by Vaughan and Vonnegut [1982] and Gales [1982]. Regrettably, the work of Corliss and many others was regarded many as a curiosity at the time. The area of sprite research clearly took a new tack when Franz et al [1990] reported the recorded television image of an "upward electrical discharge". Intending to simply test a new low-light video camera for physics research work, their work was a product of nearly complete chance. It stimulated a variety of research organizations from the university to government level to begin a systematic study of these events. The Franz work is considered by most to mark the real beginning of C-I research. 3. Current Theories / Hypotheses In each of the following discussions, the intention is to provide the reader with some background into the early theoretical work that has been accomplished thus far. For a full discussion of these theories, see the applicable authors. Key points from each theory will be provided. Several theories regarding C-I development / genesis exist. Probably the earliest effort was provided by Professor C.T.R Wilson , Royal Society of London [1925, 1956], who developed an overall theory of thundercloud electrification, which is widely regarded as a "definitive statement as to the electrical state of thunderstorms" [Wallace and Hobbs, 1977] a) Wilson's Thundercloud Electric Field Theory Wilson [1925] started a general discussion of "the electric field of a thundercloud" by stating: "The electric field of the cloud may cause ionization at great heights, the result being continuous or discontinuous discharge between the cloud and the upper atmosphere ...... The charges separated in the thundercloud may re-combine directly by a short-circuiting discharge within the cloud or by continuous or discontinuous discharges through external circuits, one such circuit including the earth and the upper atmosphere...." [Wilson, 1925] When Wilson referred to the "upper atmosphere", he was specifically pointing to the 60-80 km range. This serves as the first hypothetical suggestion that electrical disturbances were occurring at this range in the atmosphere as a direct result of active thunderstorms. In his later, more comprehensive work on thundercloud electricity, Wilson [1956] further went on to describe that "...as soon as the cloud has acquired an appreciable positive electric moment ...., external ionization currents come into action in three regions." Wilson goes on to explain these three regions, one of which is "... the current between the top of the cloud and the ionosphere" [Wilson, 1956]. Wilson argued that this is an important consideration, since "...the effect of the external ionization currents is to increase each of the two main charges of the cloud.......". The main thrust of Wilson's material set forth here is based on a complex - but classical - electrodynamic analysis of the entire cloud/atmosphere complex. Wilson completed his treatise on this subject by dedicating an entire section, entitled "DISCHARGE BETWEEN CLOUD AND UPPER ATMOSPHERE". In his words: "It is quite possible that a discharge between the top of the cloud and the ionosphere is a normal accompaniment of a lightning discharge to earth. Consider first, however, what will happen if no such upper discharge occurs." [Wilson, 1956] Wilson provided an argument that C-I events must take place, since their absence would cause a condition that is not observed normally - "...the regeneration of the main field of the cloud , an accumulation of negative charge occurring where their fall is retarded or stopped by the upward air stream". As further proof to his argument, the following discussion was provided: "There have been a number of reports of ordinary lightning discharges extending upwards from the top of a thundercloud. What is likely to be a more normal accompaniment of a discharge to earth, but one which is only likely to be visible under very special conditions, is a diffuse discharge between the top of the cloud and the upper atmosphere. .........many years ago I observed what appeared to be discharges of this kind from a thundercloud below the horizon There were diffuse fan-shaped flashes of greenish color extending up into a clear sky." [Wilson, 1956] Another radical idea was offered: C-I events may actually cause (or initiate) normal intracloud and/or cloud -to- ground lightning: "It is, on the other hand, possible that a lightning discharge to earth from the base of the cloud may be initiated by a discharge above the cloud. A large potential difference between the top of the cloud and the upper atmosphere will drag down negative ions from the very large supply existing in the ionosphere." "There is obviously a limit to the potential which can be reached in a thundercloud. At a height where the pressure is half an atmosphere the limit set by the sparking potential would be about 12 x 109 V [Volts]. A potential of one-tenth of this, giving the equivalent of a field of 3000 V/cm at normal pressure, could hardly fail to cause a discharge initiated by accelerated electrons in the upper atmosphere. The maximum potential attainable in a thundercloud cannot mush exceed this limit of about 109V." [Wilson , 1956] So, in summary, Wilson’s theory not only predicted the existence of C-I events, but actually argued that these are a profoundly important part of the entire electrification process of a thundercloud. In addition,there appears to be a potential symbiotic cause-and-effect relationship between conventional lightning and C-I events: each can possibly cause the other. b) Roussel-Dupre's theory of CosmicRay excitation / Gamma Ray emission Measurments from NASA’s Compton Gamma Ray Observatory (GRO) of Gamma Rays from intense thunderstorms have lead some scientists to speculate as to the specific mechanism that actually stimulates the C-I event at the moment in intiation. In a recent publication, Robert Roussel-Dupre’ of Los Alamos National Laboratory has commented : "Usually, the electrons and ions in this region [above the thundercloud] will quickly recombine, annulling the [electric] field. However, if an electron is produced with enough energy to knock more of its kin from neighboring atoms, an avalanche of of charge can ensue. The newly freed electrons, pulled upward along the field lines, bump into atmospheric molecules, which then fluoresce at visible wavelengths. Indeed, studies have shown that the red hues of sprites come from glowing nitrogen molecules (N2). The gamma rays come about as the high- speed electrons [sometimes referred to as "Beta Particles"] are deflected by other charged particles .....while radio pulses picked up by ALEXIS [a new experimental satellite] are generated at certain points in the electrons upward journey. " [Roth, 1996] While there are numerous different ideas as to how the initial "seed electron" starts out, but Roussel-Dupre' provides a scenario where cosmic rays are given credit - "these high-energy extraterrestrial particles have long been known to knock electrons from atoms and molecules in the Earth's upper atmosphere." [Roth, 1996] c) Meteorites One of the more obscure hypotheses regarding C-I generation is the one offered by Muller [1995] who argued: "However, there is another possible triggering phenomena: meteors. Meteors ionize large paths of air, and even if the ionization path does not quite reach the thunderhead, the path could trigger [electrical] breakdown........ We postulate that the mesosphere behaves like a triggered spark chamber. Downward lightning suddenly increases the electric field above a thunder cloud. Only when such lightning is roughly coincident with the arrival of a meteor above the cloud do we get a red sprite. Because the ionization lasts for several seconds, the coincidence does not have to be exact." [Muller, 1995] d) Others One well regarded theory regarding the appearance of elves is EMP. Theoretical calculations from researchers at Tohoku University have determined that the time between lightning flash and elve appearance ( less than 1 microsecond ) fits the right time interval for an electromagnetic pulse to reach the ionosphere, and possibly cause an elve [Kerr, 1995]. Sprites, on the other hand, are not affected by this, apparently. It has been determined that "....sprites lag the huge positive lightning stroke triggering them by several milliseconds. That's much longer than it would take for the electromagnetic pulse from a lightning stroke to arrive at the altitude of a sprite" [Kerr, 1995]. For the most part, Sprites are considered to follow a electrostatic model that is very close to that proposed by Wilson. The timing of a sprite with respect to a lightning bolt tends to support this idea. B. Why Study Cloud -to- Ionosphere events? The C-I event may seem like a fanciful apparition, worthy of just simple curiosity, but a careful look at some important factors is needed before we dismiss these marvelous events. To start off, we will look at the immediate impact that a C-I event may have on the middle atmosphere. After this, we will briefly touch on possible negative results for aircraft operating above a thunderstorm. Finally, a review of some issues regarding atmospheric electricity. 1. Possible Impacts on Chemistry of Upper Atmosphere To begin this discussion, we must first determine what part of the atmosphere - exactly - do most C-I events occur? There has been uniform agreement that sprites, blue jets, and elves occur in an altitude range from as low as 40 km to as high as 110 km. This incorporates the upper stratosphere , through the entire mesosphere. This includes the lower end of the ionosphere, and specifically the D and E layers. See Table 1 below for the heights of each of the ionosperic layers. Figure 2 will provide a quick way of placing each of these layers within the context of the entire atmosphere. __________________________________________________________________ Region Heights (km) Electron Density Principal (cm-3) Ions __________________________________________________________________ D < 90 103 to 104 NO+ E 90-140 105 NO+,O2+ F1 } >140 Maximum of 106 NO+,O+, F2 from 250 to 500km O2+,N2+ __________________________________________________________________ Ionospheric Regions TABLE 1 [Iribarne anf Cho, 1980] Having an overview to the ionosphere, what are the most common gas species found in the D and E regions? As a rule, both regions have N2, O2, NO, and O as the most common . The key question is as follows: what happens chemically when we add beta particles (high energy electrons, such as with a sprite) to this chemical soup? While there are so many potential reactons to consider, look at the following reactions from Iribrane, [1980]. Note that e represents a single electron, and M is any kind of "third body" atom or molecule. (I) O+ + e + M ==> O + M* (II) O2+ + e ==> O + O (III) NO+ + e ==> N + O (IV) N2+ + e ==> N + N (V) O2 + e + M ==> O2- + M* (VI) O3+O ==> 2O2 Note in particular equations (II), (III), and (IV). Here, we have dissociative recombination - destroying molecular ions to produce neutral atomic species. Equation (I) also clearly destroys ions as well. In the case of (I), the species M has energy added to it - hence the "*" symbol to denote the increased energy. This aded energy is due to the recombination of the O+ ion with the electron. Equation (V) is a special case of the D region in particular. The important item to note is the obvious impact that beta particles have on ionospheric chemistry. As a final comment on this issue, look at equation (VI). You may note that there are no beta particles in this equation. Further, ozone is the first term. Note that this equation provides one of the means for stratospheric ozone to be destroyed. Also, keep in mind that the first five equations are still valid reactions even in the mid-stratosphere, so that a sprite or blue jet - thrusting numerous beta particles upward, is causing neutral atomic oxygen to be produced. This, in turn, affects ozone concentration. While there is no intention (by the author) to cause a sudden concern for the "threat" to the ozone layer that is imposed by a C-I event, it is worthwhile to note that there could be a series of complex chemical reactions taking place that have a significant impact on middle and upper atmospheric chemistry. 2. Impact on High Altitude Aircraft and Spacecraft As was discussed during the Roussel-Dupre' theories, C-I events are associated with gamma radiation, in addition to natural beta particle radiation. Neither of these influences would be considered good for aircraft pilots/passengers, or astronauts (although the astronaut is clearly better protected). Also , gamma radiation tends to cause problems for highly sensitive electronic equipment. Solar events of a similar nature have, in the past, caused serious problems for orbiting satellites - going so far as to reset key pieces of equipment without human controllers even realizing it. It would not be difficult to calcuate the theoretical electrical field for an aircraft passing through such a system, thus enabling planners to assess the potential difference to which aircraft, personnel, and equipment would be subjected (See Appendix A for such an example). 3. Insight into electrical charge distribution / interaction in the Atmosphere Much has already been written regarding the electrical charge distribution associtated with sprites. The work of Wilson and Roussel-Dupre' provide ample motivation in this arena. As we continue our study of C-I events, we will undoubtedly observe either the confirmation of Wilson's theories, or we may see new truths yet. C. Current Observation Efforts 1. Video a) Ground based observations Some of the most compelling observations and discoveries have been made at a NASA funded laboratory at the Yucca Ridge Field Station (YRFS) in northern Colorado. This location is situated on a high mountain top, and provides excellent coverage for a large area. Here, special Low Light Television (LLTV) imagery has been recorded. LLTV normally consists of a special photocathode multiplier tube which enhances the light emitted. Incoming photons are converted to electrons, then the energy of these electrons is increased, then converted back into higher energy photons - thus yielding a brighter image. Usually, LLTV equipment is configured with special optical filters. These filters take advantage of energy emitted from a variety of atmospheric gaseous constituents, such as N2, O2, etc. In our work, we primarily looked at imagery using a filter for energy emitted at 7774 Angtroms - a common frequency for atomic oxygen, otherwise referred to as OI (which refers simply to conventional atomic oxygen. If this were ionized oxygen {one electron missing}, then the symbol would be OII. Ionized oxygen {two electrons missing}would be OIII, and so on [Harrison, 1969]). In addition to conventional video work, spectrographic data has been collected, and has already answered some of the questions that have been haunting researchers for some time [Mende et al , 1995]. This work has been accomplished by the use of the slit spectrograph. Chief among these discoveries has been the confirmation of the source of the red color associated with sprites : electron collisions with N2 molecules in the stratosphere and mesosphere. b) Aircraft measurements Researchers at the University of Alaska have also been conducting a variety of observation efforts using LLTV and other special video and spectrographic equipment. What is distinctive about this effort is the ability of two different aircraft - each observing simultaneously - to accurately pinpoint the location of C-I events. By maintaining course and speed relative to each other properly, each can be on a path normal to each other, allowing for easy triangulation. Also, knowledge of azimuth and elevation - as well as plane altitude - allow for more precise determinations of C-I altitude - an important item to know in order to understand the overall interaction. [Sentman et all, 1994] c) Spacecraft imagery / data Since even before the Franz paper of 1990, a number of groups have been actively engaged in C-I event observations, analysis, and research in space. One actively interested party is the NASA Marshall Space Flight Center, where work from Boeck el al [1995], and the prolific writing of Vaughan [1982, 1989, 1992, 1995] have provided much insight. Many of the NASA efforts have focused on visual observations from the Space Shuttle. Other promising data has come from the Compton Gamma Ray Observatory, on orbit since 1991. The Compton Observatory has unexpectedly been bombarded by gamma radiation from the planet surface. Referred to as "Terrestrial Gamma-ray Flashes or (TGF's)", these are short (in the order of milliseconds) blasts of gamma ray radiation that are clearly related to intense thunderstorm activity [Horsack, 1996]. C-I events, and blue jets in particular, are suspected as possibly related to this type of event [Zimmer, 1995]. 2. VLF detection During the last two years, exciting work has been completed with respect to the identification of sprites using a Very Low Frequency (VLF - 5 to 50 kHz ) omni-directional signal receiver. Here, standard VLF radio waves are transmitted in to the ionosphere, and these waves can travel long distances at this altitude, due to the electromagnetic wave ducting that occurs in the ionosphere. The occurrence of a red sprite has been shown to correlate to disturbances in the received VLF wave. The wave guide is scattered a great deal by the C-I, causing a distinctive perturbation pattern for VLF signals. Using only a single VLF receiver, it has been demonstrated that sprites can be located within 100 km, and 90 degrees in azimuth. Adding a network of such receivers can significantly improve the precision of these measurements. [Dowden et al, 1996]. Initial work has shown that it is possible to discern both sprites and elves in the VLF signal [Dowden et al, 1995] II. OBSERVATION EFFORTS AT CREIGHTON UNIVERSITY C-I observation efforts at Creighton University started in late May 1996. Initially, our intent was to operate solely from a single location atop the building of the Atmospheric Science Department in downtown Omaha. This location offered a good view of potential thunderstorms from the Northwest , through the North, and through the East. However, due to light effects from the greater Omaha Metropolitan area, we were unable to adequately visualize distant thunderstorm imagery - we would be able to see only the most brilliant flashes from C-I events. Later, a series of new sites was chosen. Our intent was to find a location that had a ready electric power supply, as little city lighting as available, and decent elevation, such as on a hill or tall building. I will continue with a summary of the details surrounding our efforts. A. Equipment used The primary piece was the XYBION IMC-201 Multispectral Video Camera. Two of these cameras (and some other equipment) were provided by Los Alamos National Laboratory for the purpose of recording C-I imagery. These cameras have a rotating "filter wheel" - a wheel containing several different opaque optical filters. Each filter is designed to only detect electromagnetic radiation at certain wavelengths. The primary camera has six optical filters, with spectral characteristics as shown in Table 2. The basic camera can be seen in figure 3.Our primary efforts focused around filter (or channel) number 5, at 7774 angstroms - one of the atomic oxygen lines. This was chosen on the ______________________________________________________________ Filter # Gas Species Wavelength (Angstroms) 1 N2+ 4278 (+/- 1.87%) 2 HI 4861 (+/- 1.87%) 3 OI 5571 (+/- 1.87%) 4 OI 6300 (+/- 1.87%) 5 OI 7774 (+/- 1.87%) 6 OH 7820 (+/- 1.87%) . _______________________________________________________________ XYBION IMC-201 Camera Spectral Characteristics Table 2 sole basis that this channel provided the best looking imagery when compared to the other five filters and their respective imagery. The term "best looking" should be interpreted to mean best gray shade contrast - the camera will eventually produce a digitized image from the video input in an 8-bit graphic image (256 gray shades). Each of these images is the exact same resolution - 756 (Horizontal) pixels by 485 (Vertical) pixels, so the only real issue was the determination of adequate contrast. Channel 5 won easily: after trying to image an active thunderstorm in late May 96, we noted that channels 1,2,3,4, and 6 were not able to provide intelligible imagery. Thus, the decision was made to use this channel on a consistent basis - in order to have some form of "baselined" imagery. The specific details of camera operation were controlled by a touchpad on the reat plate of the IMC-201, and the resultant imagery was sent to a VCR/TV combination - as depicted. The VCR recorded the imagery in standard VHS format, for post-analysis later. Attempts were made to record rough geographic and navigational details. With the camera mounted on a tripod, the camera field of view (FOV) , azimuth (with respect magnetic north), elevation, and rough position were recorded. Geographic notes were taken of surrounding landmarks for future reference. Also, notes were taken on the time. No attmept was made to correct the camera's internal clock, but a time difference of 7 minutes, 32 seconds was noted (the system time, for example, may say 04:07:32 GMT when it is really 04:00:00 GMT). The primary difficulty we experienced lay in the inital set-up of the entire camera/TV/VCR, which required some minor re-engineering. The post analysis of the VCR tapes was conducted using a special slow-motion VCR machine. This high quality machine gave us the chance to look at our imagery in a slower manner, frame by frame. Our ability to make observations of the recorded sprite imagery was improved greatly. B. Method of Employment Again, our intent was to operate solely from a single location atop the building of the Atmospheric Science Department in downtown Omaha, and due to unfavorable lighting conditions in downtown Omaha, our vantage point had limited utility. We set out to find a series of different locations that would provide a better look with few background lights from towns and cities, and a wide azimuthal look angle. One such place was found in Bellevue, Nebraska, just south of Omaha. Our efforts consisted of carrying the camera, and associated equipment from Creighton to the Bellevue site, where we set up the the camera on a hill located near 41o09'30"N and 095o57'20"W (position only accurate to within +/- 10") at over 1110 feet above man sea level. At this location, we had a good view from the South-Southwest, through the West, to the North-Northwest, with comparatively less town light interference from the surrounding country towns. Our view to the Southwest (Azimuth: 240o magnetic) was especially good- essentially, there were no significant lights to cause concern - just some repetitive aviation beacons, which were relatively low on the horizon and easy to distinguish fro other lights. C. Results 1. Multiple events from August 15, 1996 a) Synoptic Weather Scenario b) Location / Description of local conditions c) Imagery / Information 2. Events from August 22, 1996 a) Synoptic Weather Scenario b) Location / Description of local conditions c) Imagery / Information 3. Miscellaneous III. LESSONS LEARNED / AREAS FOR FUTURE IMPROVEMENT A. Multispectral Data 1. Conventional visual data 2. Low-light Video 3. Multi-filter imagery 4. Image analysis B. Utility of Digital Radar data and NLDN information C. VLF data correlation D. Additional resources needed 1. Personnel 2. Power supply 3. Location and number of Observation Sites IV. CONCLUSIONS In summary, efforts at Creighton University have yielded some hopeful results. We were able to store limited types of imagery for a variety of C-I phenomena. We observed the events at different times of the year, and under somewhat differing conditions. Specifically, we observed obvious Red Sprites, (possible) blue jets, and certainly at least two instances of elves. We were able to compute rough altitudes for the tops of these flashes, and correlated them with distinct meteorological phenomenon. Also, there is now a clearer sense of how to capture this imagery, and an improved plan of attack for the systematic pursuit of these strange "lights-in-the-sky". We know what conditions are best suited for sprite observation. We have a good idea of the kind of new data and imagery will be needed in the future to better understand these phenomena. Finally, we have a working hypothesis to explore for future validation with respect to the formation of these C-I events. As data collection efforts improve, we hope to refine our understanding of these atmospheric events. BIBLIOGRAPHY Boeck, W.L. O.H. Vaughn, Jr.,R. Blakeslee, B. Vonnegut, M. Brook, and J. 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