Remote Measurements of Lightning Current and Charge Transfer with Low Frequency ElectroMagnetic (EM) Sensors

Duke University, Durham NC

Investigators

Abstract

Despite at least several centuries of scientific inquiry, lightning remains an important and interesting target for modern research. Measurements of lightning associated with unusual phenomena such as sprites have anecdotally suggested that large currents and charge transfer in lightning strokes may be more common than previously appreciated, but little is known about current and charge transfer upper limits, the geographic distribution of these energetic events, and their associated meteorology. In fact, few quantitative measurements of charge transfer and continuing currents have been made in lightning of any kind. The overwhelming majority of lightning measurements have been made in limited geographic areas with short range or local instrumentation that are ideal for studying the details of individual flashes, but not for observing lightning processes over wider regions. Substantial progress over the past several years (partly with support of a predecessor NSF grant) has been made in developing techniques for long range, quantitative lightning current and charge transfer remote sensing. With these capabilities now essentially fully developed, a three-year research effort will apply these lightning remote sensing techniques to complete focused tasks related to the following topics: the mechanisms behind and implications of terrestrial gamma ray flashes; the basic statistics and meteorological variability of lightning charge transfer and continuing currents; novel measurements of the total storm-integrated lightning charge transfer to ground; and the analysis of correlated remote lightning charge and current measurements with high speed lightning video and lightning mapping array data. The intellectual merit of the measurements is that they will improve our understanding of the quantitative variability of lightning, and they will identify the meteorological conditions responsible for unusually strong lightning. The presence of certain classes of lightning charge transfer and continuing current characteristics in storms may also provide insight into fundamental storm electrical structure and development. The characteristics of lightning associated with terrestrial gamma ray flashes will be quantified, leading to a better understanding of the phenomenon and its possible link to lightning initiation. The technical approach leverages past experimental measurements that have already been made, and new measurements that will be made with existing instrumentation. This ensures the research can be completed cost-effectively. The research has broader impact in that it provides an excellent training opportunity for students with a balance of data-driven analysis, experiments and hardware, and theoretical modeling. One graduate student will be trained with support from this project, and undergraduate research assistants funded by Duke fellowships will also be involved. Research in this area has a high public profile because of broad interest in lightning and its effects. Past research in this area by the PI has generated media interest resulting in numerous press releases, media articles, and even two television appearances. Every effort will be made to ensure the broadest possible dissemination of the results. The measurements are a resource to the broader atmospheric electricity and atmospheric science communities and will be used in presentations and publications by multiple investigators as part of national and international collaborations. Data from the effort will be treated as a resource to the community and will continue to be made available to others. The measurements also have significant practical links to better understanding lightning hazards and could help better identify and mitigate the impact of lightning on human activities. The effort will also aid an ongoing collaboration to commercialize some of these lightning remote sensing techniques with QUASAR, Inc. (San Diego, CA).