CEDAR: Modeling Studies of Infrasonic Waves from Thunderstorms and Aurora

CEDAR：雷暴和极光次声波的建模研究

• 批准号: 0836391
• 负责人: Victor Pasko
• 金额: $ 25.35万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-01 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0836391&HistoricalAwards=false
• 关键词: CEDAR; Modeling; Studies; Infrasonic; Waves

This project is a three year effort to theoretically investigate mechanisms and effects of infrasonic waves generated by thunderstorms and aurora. The infrasonic waves correspond to acoustic waves in the frequency range 0.02-10 Hz. There is strong experimental evidence that thunderstorms and aurora represent significant sources of infrasonic wave activity spanning a broad altitude range from the troposphere up to the thermosphere. This evidence includes electrostatic production of 0.1-1 Hz infrasonic waves from thunderstorms, recent discovery of infrasound from lightning induced transient luminous events in the mesosphere called sprites, and radiation of infrasonic waves from supersonic auroral arcs and pulsating aurora. The project aims to characterize and quantify the observed infrasonic signals by undertaking a focused two-dimensional numerical modeling effort. It will address a limited set of unsolved problems related to infrasonic wave production by thunderstorms and aurora. The outstanding scientific questions to be pursued are: (1) What is the mechanism for the compression and rarefaction infrasonic pulses with periods 0.5 to 1 sec produced in association with lightning discharges? What is the fate and predicted signature of these pulses as they propagate downward and upward from thunderclouds and reach a remote observer after reflections from the ground and thermosphere? (2) What is the mechanism of the recently discovered infrasound radiation from sprites? Which physical factors, including both infrasound generation and propagation factors, contribute to formation of the chirp-like signatures that are observed? What are the specific features of observed waveforms, which would allow a remote observer to discriminate between infrasound radiation coming from thunderclouds at low altitudes and those from sprites? (3) What is the temporal and spatial structure of the body force acting on neutral air in auroral arcs that move with supersonic speeds, leading to auroral infrasound waves observed on the ground? What is the mechanism of the recently observed infrasound signals from pulsating aurora? Specific activities include development of a new efficient two-dimensional model of infrasound propagation using finite-difference time-domain techniques. The new model will be fully non-linear and will account for realistic temperature and wind structure in the Earth's atmosphere as well as for altitude dependent dissipation effects. The model will follow the fate of infrasonic wave packets at they propagate, reflect, and dissipate in the atmosphere in order to interpret existing published observations and to make specific predictions for future observations.

本项目历时三年，从理论上研究雷暴和极光产生次声波的机理和影响。次声波对应于频率范围为0.02-10赫兹的声波。有强有力的实验证据表明，雷暴和极光是次声波活动的重要来源，它跨越从对流层到热层的广泛高度范围。这些证据包括雷暴静电产生的0.1-1 Hz次声波，最近发现的中间层闪电引起的瞬态发光事件（称为精灵）次声波，以及超音速极光弧和脉动极光产生的次声波辐射。该项目旨在通过进行集中的二维数值模拟工作来表征和量化观察到的次声信号。它将解决有关雷暴和极光产生次声波的有限的尚未解决的问题。需要解决的突出的科学问题是：(1)闪电放电产生周期为0.5秒至1秒的次声脉冲的压缩和稀疏的机制是什么？当这些脉冲从雷雨云向下和向上传播，经过地面和热层的反射到达远程观测者时，它们的命运和预测特征是什么？(2)最近发现的精灵次声辐射的机制是什么？哪些物理因素，包括次声产生和传播因素，有助于形成所观察到的啁啾样特征？观察到的波形的具体特征是什么，这将允许远程观察者区分来自低空雷雨云和精灵的次声辐射？(3)在以超音速移动的极光弧中，作用于中性空气的力的时空结构是什么，导致在地面上观测到极光次声波？最近观测到的脉动极光的次声信号的机制是什么？具体活动包括利用时域有限差分技术开发一种新的高效二维次声传播模型。新模型将是完全非线性的，并将考虑地球大气中实际的温度和风结构以及高度相关的消散效应。该模型将跟踪次声波包在大气中传播、反射和消散的命运，以便解释现有发表的观测结果，并为未来的观测做出具体预测。