| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | July 7, 2011 |
| Latest Amendment Date: | July 7, 2011 |
| Award Number: | 1110030 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Chungu Lu
AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | July 15, 2011 |
| End Date: | June 30, 2015 (Estimated) |
| Total Intended Award Amount: | $710,646.00 |
| Total Awarded Amount to Date: | $710,646.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
113 FALKNER UNIVERSITY MS US 38677-9704 (662)915-7482 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
113 FALKNER UNIVERSITY MS US 38677-9704 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Physical & Dynamic Meteorology |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
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 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.
By using a unique array of sensors, this project aims to gather new information about lightning initiation and lightning propagation to help explain how these two fundamental aspects of lightning may work. The measurements 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.
Intellectual merits:
This NSF project is an extension of a recently completed NSF EArly-concept Grant for Exploratory Research award - "EAGER Multi-Frequency Studies of Lightning Initiation and Propagation" - and builds on the successful results of that initial award. The completed EAGER project used lightning observations with five different measurement systems. The enhanced observational scheme for this NSF project will expand EAGER project with eight systems to observe lightning processes: (1) "slow" antennas, (2) "fast" antennas, (3) a network of seven crossed-loop magnetic sensors, (4) the KSC electric field mill network, (5) the KSC Lightning Detection And Ranging (LDAR) system, (6) the KSC Cloud-to-Ground Lightning Surveillance System (CGLSS), (7) high-speed video cameras (at 54,000 frames/second), (8) VHF radio emissions, and (9) fast electric field changes (dE/dt). All nine sensors look at electromagnetic changes caused by lightning as it accelerates and moves charge; the sensors operate across a wide and partially overlapping range of electromagnetic frequencies.
The various sensors respond to different parts of a flash: some parts are only a few meters in length while others are as long as a several thousand meters. There are two key features of the sensor array that will be especially useful in this new lightning investigation. First, the array will be able to determine the previously unknown locations of the long, fast electromagnetic pulses that occur during the initiation of both in-cloud and cloud-to-ground lightning flashes. Second, the high-speed video images of a propagating lightning flash will literally give us visual pictures to combine with and compare with the data from the other 8 sensors. Overall, the intellectual merit of the project stems from combining the data from these nine sensors to provide new insights into how lightning initiation and lightning propagation work.
Broader impacts:
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, two other graduate students just beginning their training, and two undergraduate physics students interested in being involved in scientific research. The training involves techniques that are specific to electromagnetic measurements of lightning as well as techniques that are generally applicable in many situations (including computer programming, computer control of instruments, computer modeling, etc.). The results of this project will also be broadly disseminated in the peer-reviewed literature.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Lightning is one of the worst natural hazards, killing more people in the USA on average than hurricanes or tornadoes Although much has been learned about lightning, 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.
The goal of this NSF project—“Multi-Frequency Studies of Lightning Initiation and Propagation”—was to learn more about how lightning starts and how it travels. In July and August of 2010 and 2011, we collected lightning data at the Kennedy Space Center (KSC) in Florida with 7 types of sensors, which can be thought of as 7 different ‘eyes’ for looking at lightning. The multiple eyes were all time-synchronized and included 4 sensor arrays measuring radio emissions of lightning at different frequencies (these emissions are the static that can be heard on AM radios during thunderstorms), plus an electric field measurement array, a standard speed video camera, and a high speed video camera operating at 50,000 frames per second. Two of the radio arrays allowed us to locate where a lightning flash began. Together the arrays allowed us to track the short and long jumps that make up the developing lightning flash’s path through the cloud and across the sky. Three of the radio arrays also allowed us to determine where a flash hit the ground. The electric field array allowed us to determine how much electric charge each flash moved. The high-speed camera showed (for the first time ever) what flash initiation looks like and showed what the jumps along the path look like. Our investigations of these data have resulted in 14 refereed publications in scientific journals. A few of the key results are discussed next.
Previously, lightning has been thought to begin with the (poorly understood) “initial breakdown (IB) pulses.” In earlier studies, IB pulses had only been recorded with a single radio receiver. Their locations were not known, nor had they been seen visually. We developed a new way to use radio arrays to locate IB pulses and to determine how much current they carried. We also obtained the first-ever high-speed video images of IB pulses (see Figure 1); they appear as thin, bright lines that extend in jumps of about 100 - 200 m. The IB pulses extend the flash to a length of about 1500 m (approximately one mile); then the flash propagation transitions from “IB pulse” mode to “stepped leader” mode (discussed below). Comparing the videos with the radio emissions is helping us understand what the IB pulses are.
We discovered that lightning begins earlier that previously thought, with the earliest charge motion beginning about one-thousandth of a second (0.001 second) before the IB pulses begin. This earliest charge motion seems to start the IB pulses. The earliest charge motion itself seems to be started by a single fast radio pulse that is much shorter and smaller than an IB pulse. These data indicate that the first radio pulse and the early charge motion are the real way in which lightning begins.
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’ (See Figure 2). The return stroke is bright because it carries a large 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 (see Figure 3). In this project, UIs were found in 22 of 180 CG flashes observed with the high-speed came...
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