FINAL REPORT

Sensor System to Monitor Cloud-to-Stratosphere Electrical Discharges

 submitted to

National Aeronautics and Space Administration
John F. Kennedy Space Center
Kennedy Space Center, Florida 32899

under

NASA SBIR Phase II
Contract NAS10-12113

submitted by

Walter A. Lyons, Ph.D.
Principal Investigator

FMA Research (formerly ASTeR, Inc.)
Yucca Ridge Field Station
46050 Weld County Road 13
Ft. Collins, CO 80524
970-568-7664
walyons@frii.com
25 April 1996

 TABLE OF CONTENTS

EXECUTIVE SUMMARY


1.INTRODUCTION
2. THE 1994 AND 1995 SPRITE FIELD PROGRAMS 3.0 CASE STUDIES 4.0 METHODS OF DETECTION 5.0 CLIMATOLOGY

6.0 SUMMARY, CONCLUSIONS AND RECOMMNEDATIONS 7.0 ACKNOWLEDGMENTS

8.0 REFEENCES AND EXTENDED BIBLIOGRAPHY

APPENDICES
EXECUTIVE SUMMARY This report summarizes the findings from the Phase II SBIR project, "Sensor System to Monitor Cloud-to-Stratosphere Electrical Discharges", from the NASA Kennedy Space Center, Contract NAS10-12113. The major tasks included (1) improving the understanding of the physics of transient luminous events, (2) forecasting their occurrence, (3) developing and testing sensor systems to detect and characterize the phenomena, (4) assessing their impact including the threat posed to aerospace operations, and (5) establishing an information exchange for observations and theoretical studies. Two field programs were conducted, SPRITES'94 and SPRITES'95 which resulted in the compilation of a very large library of video, audio and digital data from a suite of optical and RF sensors. Anecdotal reports of unusual forms of 'lightning' discharging into the 'stratosphere' have been reported globally for over a century (Toynbee and Mackenzie, 1886; Lyons and Williams, 1993) and theoretically postulated (Wilson, 1925, 1956). It remained for a chance observation from a low-light video system in 1989 to actually document that such events existed (Franz et al., 1990). Subsequently, low-light video imaging systems on board the Space Shuttle (Vaughan et al., 1992; Boeck et al., 1995), on aircraft (Sentman and Wescott, 1993; Sentman et al., 1995, Wescott et al., 1995) and at fixed ground stations (Lyons 1994 a,b; 1995; 1996) have revealed that large stratospheric and mesospheric transient luminous events (TLEs) above mesoscale convective systems (MCSs) are rather common. Observations each summer since 1993 from the Yucca Ridge Field Station (YRFS), 20 km northeast of Ft. Collins, CO, have documented over 2000 such events. The YRFS field programs have documented three types of TLEs: sprites, elves and a blue jet. During 1994, the emphasis was on developing forecasting techniques and data acquisition systems. Low-light imagers were operated in conjunction with a high speed photometer and several VLF receivers. A major discovery was the strong correlation between sprites, positive polarity cloud-to-cloud (+CG) flashes, and ELF transients called Q-bursts (Boccippio et al., 1995). Initial evidence of brief ionospheric flashes (now called elves) were also found. The results from SPRITES'94 and rapidly growing interest from the scientific community resulted in the SPRITES'95 observational effort becoming a major international field program with the participation of 48 scientists from 16 organizations representing four countries. The deployment of high resolution pointing photometers (Fukunishi et al., 1996) resulted in the definitive identification of a new class of transient luminous event, elves (emissions of light and VLF perturbations from EMP sources). For the first time, a ground-based LLTV captured an apparent blue jet (Lyons, 1996). The relationship between sprites, +CGs and Q-bursts was further confirmed (Inan et al., 1995; Fullekrug et al., 1996). Distinct signatures of sprites were also found in the VLF. The presence of VLF slow tails appears to distinguish between large peak current +CGs that do and do not produce sprites (Reising et al., 1996). Blue jets are not associated with specific +CGs but may be spawned in storms having a high rate of -CG activity. The first known climatology of large peak current CGs of both polarities was prepared from 14 summer months of NLDN data. A remarkable disparately was uncovered in the distribution of large positive and large negative CGs. The positives were strongly clustered in the High Plains and Upper Midwest, the region under surveillance by the YRFS sensors. The large -CGs were concentrated in the southeastern US, especially over the waters of the Gulf and Atlantic, including the KSC region. Whether blue jets are far more common in that area is still uncertain. Using the CG climatology, an estimate was made of the chances of the Space Shuttle being involved in a sprite or elve during descent into KSC. The probability, on the order of one in hundred, is markedly higher than the chances of being directly struck by conventional lightning. Several techniques have been developed that could allow for routine monitoring of electrical discharges having a high likelihood of generating sprites or elves. The measurement of ELF transients could provide nearly global coverage, and by connecting several sensors already deployed in the U.S., the airspace over KSC could be routinely monitored for sprites and elves. Among the accomplishments of the Phase II effort, many made in conjunction with cooperating science teams, include:

1) Sprites and elves are common occurrences in certain classes of thunderstorms
2) Surface-based imagers can detect sprites at ranges up to 1000 km under ideal conditions; Triangulation confirms sprites and +CG are collocated within 50 km
3) Above the High Plains, sprites and elves only occur with large (>20,000 km2) mesoscale convective systems producing +CG events; It is possible to forecast with high accuracy those storms which will generate sprites
4) Sprites and elves are quasi-electrostatic and EMP responses respectively to +CG flashes generally having much larger than average peak current
5) The brightest portion of the sprite may have a duration on the order of 1-10 ms, followed by a long decay in luminosity; Elves are even more transient, lasting less than 1 ms
6) There are likely several additional different classes of transient luminous phenomena to be found above thunderstorms
7) Spectra confirmed the presence of the N2 first positive bands in sprites and elves
8) High resolution photometers confirmed presence of 427.8 nm band in sprites
9) Clear-cut 'VLF Sprite' signatures were discovered including the observation that those +CGs having a VLF slow tail (as measured at Palmer Station, Antarctica) had a much higher probability of being sprite producers; This suggests a key role for a continuing current in sprite-associated +CGs
10) Initial calculations indicate significant production of NO by sprites in the stratosphere/mesosphere and a potential to influence climate change processes
11) Firsts included coordinated launching of balloon-borne electric field mills into a sprite storm and attempts at radar mapping of sprites
12) Evidence of airglow enhancement from thunderstorm-generated gravity waves
13) Extensive press and media coverage (Discovery Channel, BBC, NY Times, New Scientist, Science, Discover Magazine, San Francisco Chronicle, etc.)
 Also prepared was an extensive bibliography of papers from several disciplines relevant to the observations and theoretical understanding of transient luminous events. An appendix volume presents summaries of the data sets available, and key research papers generated by the project staff and cooperating groups. A companion video describes the project and its results, along with sample 'highlights' from several of the major case study days. Follow-on studies (SPRITES'96) are being funded by the U.S. Air Force Office of Scientific Research.