Collaborative Research: Direction-Finding Measurements of LF/MF/HF Auroral Radio Emissions at South Pole

合作研究：南极 LF/MF/HF 极光无线电发射的测向测量

• 批准号: 0442335
• 负责人: Allan Weatherwax
• 金额: --
• 依托单位: Siena College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-04-01 至 2008-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0442335&HistoricalAwards=false
• 关键词: Collaborative; Research; Direction; Finding; Measurements

The proposed project is focused on improving the experimental technique currently used at South Pole for better directional detection and understanding of the sources and propagation of observed low, medium, and high frequency (50 - 5000 kHz) emissions (and specifically medium-frequency bursts) generated in the auroral ionosphere by the solar and geomagnetic activity. The studies of near-Earth electromagnetic environment is important because ionospheric plasma waves and instabilities play a direct role in mediating exchange of the energy between charged particle populations, provide effective means of remote sensing of the ionospheric and magnetospheric plasma processes and boundaries, and represent a "local laboratory" for studying emissions mechanisms which also occur in remote planetary or astrophysical plasmas. The low-noise electromagnetic environment of the South Pole Station in the above-mentioned frequency band allows to study statistically two auroral radio emissions: (a) auroral roars, a narrowband emission near the electron cyclotron harmonics; and (2) auroral MF bursts, a broadband emission associated with geomagnetic substorm onsets. A versatile waveform receiver (deployed at South Pole since 2002) captured scores of auroral roar emissions at full resolution, and numerous examples of fully resolved low-frequency auroral hiss events are now available for the study. It is proposed to complete the analysis of the high-resolution "auroral roar" and "hiss" data, but then focus on the auroral medium-frequency (MF) bursts - an outstanding mystery of the aurora because its generation mechanism is still unknown. The project plans to deploy a new digital direction-finding receiver at South Pole and use it to perform a few significant observational experiments: (1) identify features of the substorm expansion correlated with the MF bursts by tracking the azimuth of bursts' arrival as a function of time as the substorm evolves; (2) compare and validate different methods of determining substorm onsets by comparing the timing from ultra-low-frequency and optical data and MF bursts; (3) analyze multi-wavelength optical and imaging riometer data to determine characteristics of the auroral electron spectra that cause the MF burst; and (4) determine the detailed relationship between MF burst and auroral hiss emissions using digital data from perpendicular crossed antennas and the handedness of polarization (indicative of the propagation mode) of MF burst events extending below 1500 kHz. The first two experiments will help discovering new experimental methods for the substorm studies, and the rest - to focus on determining the source mechanism of the MF bursts and its relation to other radio emissions. These experiments will provide significant experimental materials for theorists to markedly advance our knowledge of the auroral radio emissions and their relation to macrophysics of various auroral phenomena..

拟议项目的重点是改进目前在南极使用的实验技术，以便更好地定向探测和了解太阳和地磁活动在极光电离层产生的观测到的低、中、高频(50-5000千赫)辐射(特别是中频爆发)的来源和传播。近地电磁环境的研究很重要，因为电离层等离子体波和不稳定性在调节带电粒子群体之间的能量交换方面发挥了直接作用，为遥感电离层和磁层等离子体过程和边界提供了有效手段，并代表了研究远程行星或天体物理等离子体中也存在的发射机制的“本地实验室”。南极站在上述频段的低噪声电磁环境允许统计地研究两种极光射电发射：(A)极光咆哮，电子回旋谐波附近的窄带发射；(2)极光中频爆发，与地磁亚暴开始有关的宽带发射。一台多功能波形接收器(自2002年以来部署在南极)以全分辨率捕获了数十次极光咆哮发射，现在有许多完全分辨的低频极光嘶嘶事件的例子可供研究。建议完成高分辨率的极光咆哮和嘶嘶数据的分析，但随后将重点放在极光中频(MF)爆发--极光的一个突出谜团上，因为它的产生机制尚不清楚。该项目计划在南极部署一台新的数字测向接收机，并利用它进行一些重要的观测实验：(1)通过跟踪亚暴的到达方位角随亚暴的演变而确定与中频爆发相关的亚暴扩展特征；(2)通过比较超低频和光学数据与中频爆发的时间比较，比较和验证确定亚暴开始的不同方法；(3)分析多波长光学和成像里程计数据，以确定引起中频爆发的极光电子谱特征；以及(4)利用垂直交叉天线的数字数据和1500 kHz以下中频爆发事件的极化利手(指示传播模式)，确定中频爆发与极光嘶嘶发射之间的详细关系。前两个实验将有助于发现亚暴研究的新实验方法，其余的实验将集中于确定中频爆发的来源机制及其与其他射电辐射的关系。这些实验将为理论家提供重要的实验材料，显著提高我们对极光射电发射及其与各种极光现象的宏观物理关系的认识。