Lightning is one of the worst natural hazards, killing more people in the USA on average than hurricanes or tornadoes [see www.nws.noaa.gov/om/hazstats.shtml] and causing substantial damage to property and sensitive equipment. Although lightning flashes have been studied for many decades, several fundamental aspects of lightning physics are still not understood, including how they begin (initiate) and how they travel (propagate) through clouds and clear air to the ground. This research project will focus on lightning initiation and lightning propagation in a new way to help explain how these two fundamental aspects of lightning may work. The measurements proposed will be made at the NASA Kennedy Space Center (KSC) in Florida. Lightning is especially frequent at KSC, causes expensive operational delays, and sometimes damages sensitive rocket and shuttle vehicles and/or facilities.
The observation scheme for this project is to use five different 'eyes' (measurement systems) to observe lightning processes: (1) slow antennas, (2) fast antennas, (3) a network of seven crossed-loop magnetic sensors, (4) the KSC field mill network and (5) the KSC Lightning Detection And Ranging (LDAR) system. All of these sensors look at the electric or magnetic changes caused by lightning as it accelerates and moves charge. The five types of sensors are well known in lightning research, but all five have never before been used together to observe flashes. The different instruments respond to different parts of a flash: some parts are only a few meters in length while others are as long as a few thousand meters. A key feature of this project will be the use of a recently developed technique for the crossed-loop sensor network that allows one to determine the location of long (~1000 meter), fast electromagnetic pulses from lightning. The locations of these long pulses, found in both in-cloud and cloud-to-ground lightning flashes, have not been known in the past.
The intellectual merit of the project stems from combining the data from these five sensors to provide new insights into how lightning initiation and lightning propagation work.
The main broader impacts of the project fall into two categories: improving lightning safety and training new scientists. Developing a better understanding of the mechanisms behind a particular hazard (lightning, in this case) can lead to new and improved ways of protecting people and property from that hazard. Lightning protection systems are primarily based in science, and determining how lightning initiates and propagates may reveal new ways to protect objects on the ground and in the air. This project will also be important for the development and training of several new scientists, including one graduate student pursuing a Ph.D. degree, and two undergraduate physics students interested in being involved in scientific research. The results of this project will also be broadly disseminated in the peer-reviewed literature.
Lightning is beautiful and awe-inspiring and also scary, destructive, and deadly. Lightning is one of the worst natural hazards, killing more people in the USA on average than hurricanes or tornadoes and causing substantial damage to property and sensitive electrical equipment. In spite of decades of study, we still do not understand exactly what physical mechanism causes the first spark of a lightning flash, how that spark grows into a conducting path (the lightning ‘channel’), or how the channel moves through cloudy and clear air. This NSF project was an EAGER (EArly-concept Grant for Exploratory Research) award entitled "EAGER Multi-Frequency Studies of Lightning Initiation and Propagation." The goal was to test a unique array of 7 sensor types as a way of gathering new information about how lightning starts and where lightning travels. The 7 sensors can be thought of as 7 different types of ‘eyes’ for looking at lightning. The multiple eyes were all time-synchronized and included three sensors measuring radio emissions of lightning in the AM radio and FM radio bands (these emissions are the static that can be heard on radios during thunderstorms), two lightning ground strike location systems, an electric field measurement array, and a high speed video camera operating at 54,000 frames per second. To test the multiple sensor concept, lightning measurements were made under this project at the NASA Kennedy Space Center (KSC) in Florida during July and August of 2010. Lightning is especially frequent at KSC, causes expensive operational delays, and sometimes damages sensitive rocket components and/or facilities. A few firsts from this project show why the test was deemed successful. Lightning initiation is a mystery, but the data collected show the earliest charge motions recorded to date. These charge motions begin 1–6 ms before the first radio emissions by the lightning flash, meaning that the earliest charge movements occur without producing radio static. These charge motions occur immediately after flash initiation, and, with further study, should give valuable information about the initiation process. The first lightning events to produce radio static are called initial breakdown pulses. They apparently signal the beginning of the lightning channel development inside the cloud, but their location and mechanism have been unknown. In this project the first known high-speed video imagery of initial breakdown pulses was recorded. Comparing these videos to the radio emissions at the same time should help determine what the initial breakdown pulses are and how they are produced by the lightning channel. Most lightning dangers are associated with flashes that strike the ground (cloud-to-ground or CG lightning). The brightest part of the CG flash is usually the upward moving ‘return stroke.’ The return stroke is bright because it carries that largest electrical current, and it is this large current that is so hazardous to people and equipment. KSC has its own system (CGLSS) to locate the return stroke locations. During our data collection we discovered a new kind of return stroke that we call Upward Illumination (UI) or UI-type return stroke. In this project, UIs were found in 4 of 10 CG flashes observed with the high-speed camera. Although one of the ground-strike systems did detect all the UIs, none were detected by CGLSS. Additional study is needed to improve the detection of UI-type return strokes. In summary, this NSF award was successful in showing that multiple sensor arrays collecting time-correlated lightning data with high time resolution can provide new information about how lightning works.
