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CEDAR: Modification of Ionosphere by Lightning ElectroMagnetic Pulse (LEMP): Dependence on Lightning Type, Stroke Order, and Other Factors

CEDAR：闪电电磁脉冲 (LEMP) 对电离层的改变：取决于闪电类型、行程顺序和其他因素

基本信息

批准号：
2055178
负责人：
Vladimir Rakov
金额：
$ 39.99万
依托单位：
University of Florida
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2021
资助国家：
美国
起止时间：
2021-06-01 至 2025-05-31
项目状态：
未结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2055178&HistoricalAwards=false
关键词：
CEDAR Modification Ionosphere Lightning ElectroMagnetic

项目摘要

Atmospheric lightning is a very familiar phenomenon seen during thunderstorms. However, it is not well-known that lightning strokes seen in the lower atmosphere could also travel upward as an electromagnetic pulse, modifying the properties of the upper atmosphere. The study of lightnings is especially useful for the understanding of the ionosphere, which is the layer of atmosphere above 50 miles altitude that has abundance of charged particles such as ions and electrons. Cumulative effects of lightnings could potentially modify the ionosphere, which in turn affect radio communication and global navigation. This project will carry out a cross-disciplinary study of the modification of ionosphere by Lightning Electro Magnetic Pulse (LEMP). The atmospheric conductivity profile that largely determines the apparent ionospheric reflection height is expected to be modified as a result of ionization caused by LEMP. This modification will be detected via comparison of conductivity profiles inferred from electromagnetic field signatures (including skywaves) of individual lightning strokes occurring within the same flash. There is some evidence of cumulative effect of multiple strokes in lowering the apparent ionospheric reflection height. For the first time, ionospheric reflection heights estimated using in-cloud lightning pulses (elevated sources) and return-stroke pulses in cloud-to-ground flashes (CGs) (near-ground-level sources) of different polarity will be compared. This project will attempt to answer the following new scientific questions (SQs) that are relevant to the primary objective of the CEDAR Program, with emphasis on perturbations (LEMPs) that propagate upward from the lower atmosphere: 1. How is the atmospheric conductivity profile changing on the time scale of individual lightning flash? 2. What are the limits of applicability of the Hetzian dipole model that is widely used in studying lightning interaction with the ionosphere?3. Why is the apparent ionospheric reflection height for positive lightning larger than for negative lightning in the same thunderstorm? 4. How important are lightning processes other than negative return strokes in CGs in disturbing the lower ionosphere? Wideband LEMPs will be recorded at the well-established facilities (Lightning Observatory in Gainesville and Golf Course Station) in Florida, at distances ranging from 50 to 500 km, in different seasons, over land and over sea, under both daytime and nighttime conditions. Data acquired will be used to address SQs 1, 3 and 4. A Finite-Difference Time-Domain (FDTD) model of LEMP propagation in the Earth-ionosphere waveguide in the spherical coordinate system will be used to address SQs 1 to 3. An optimization procedure to find best-fit parameters of equivalent exponential atmospheric conductivity profile from measured LEMP waveforms (including skywaves) produced by individual strokes of a flash will be used for SQ 1. The model will employ realistic lightning sources and cover an essentially full frequency bandwidth of interest (up to hundreds of kilohertz). Research results will be used in the popular University of Florida senior undergraduate/graduate course “Lightning”. The project researchers will remain committed to high-school science education and to enhancement of public awareness of lightning hazards. The studies will continue to foster international collaboration on FDTD modeling. The results of this project will have implications for other disciplines, including radio communication, ionospheric remote sensing, assessment of methods for artificial modification of the ionosphere, ionospheric chemistry, and ionospheric plasma physics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

大气闪电是雷暴期间非常常见的现象。然而，人们并不知道在低层大气中看到的闪电也可以作为电磁脉冲向上传播，改变高层大气的性质。对闪电的研究对于理解电离层特别有用，电离层是海拔50英里以上的大气层，具有丰富的带电粒子，如离子和电子。闪电的累积效应可能会改变电离层，进而影响无线电通信和全球导航。该项目将对闪电电磁脉冲（LEMP）对电离层的影响进行跨学科研究。大气电导率分布在很大程度上决定了表观电离层反射高度，预计由于LEMP引起的电离作用而被修改。这种修改将通过比较从同一闪光中发生的单个雷击的电磁场特征（包括天波）推断的电导率剖面来检测。有一些证据表明，在降低视电离层反射高度的多次中风的累积效应。将首次比较使用云中闪电脉冲（高架源）和不同极性的云地闪（CG）（近地面源）回击脉冲估算的电离层反射高度。该项目将试图回答以下与CEDAR计划的主要目标相关的新科学问题（SQ），重点是从低层大气向上传播的扰动（LEMP）：1。大气电导率剖面在单个闪电的时间尺度上是如何变化的？2.广泛用于研究闪电与电离层相互作用的赫兹偶极子模型的适用范围有哪些限制？3.为什么在同一雷暴中，正闪电的电离层视反射高度大于负闪电的视反射高度？4.在扰动低电离层方面，闪电过程（而非CG中的负回击）有多重要？宽带LEMP将在佛罗里达完善的设施（盖恩斯维尔的闪电观测站和高尔夫球场站）记录，距离从50到500公里，在不同的季节，在陆地和海上，在白天和夜间的条件下。采集的数据将用于解决SQ 1、3和4。将使用球坐标系中地球电离层波导中LEMP传播的时域有限差分（FDTD）模型来解决SQ 1至SQ 3。SQ 1将采用一种优化程序，从测量的闪电脉冲波形（包括天波）中找到等效指数大气电导率剖面的最佳拟合参数。该模型将采用真实的闪电源，并覆盖基本上完整的频率带宽（高达数百千赫）。研究成果将用于受欢迎的佛罗里达大学高级本科/研究生课程“闪电”。项目研究人员将继续致力于高中科学教育和提高公众对雷电危害的认识。这些研究将继续促进FDTD建模方面的国际合作。该项目的成果将对其他学科产生影响，包括无线电通信、电离层遥感、电离层人工修改方法的评估、电离层化学和电离层等离子体物理学。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。