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

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、高频率（50 - 5000千赫）发射（特别是中频爆发）的来源和传播。对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介导带电粒子群之间的能量交换方面发挥着直接作用，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，并为研究也发生在遥远的行星或天体物理等离子体中的发射机制提供了“当地实验室”。南极站在上述频带内的低噪声电磁环境使人们能够对两种极光无线电发射进行统计研究：（a）极光咆哮，即电子回旋谐波附近的窄带发射;（2）极光中频爆发，即与地磁亚暴爆发有关的宽带发射。一个多功能波形接收器（自2002年以来部署在南极）以全分辨率捕获了数十个极光轰鸣发射，现在有许多完全分辨的低频极光嘶嘶声事件的例子可供研究。建议完成对高分辨率“极光轰鸣”和“嘶嘶声”数据的分析，但随后将重点放在极光中频（MF）爆发上-这是极光的一个突出谜团，因为其产生机制仍然未知。该项目计划在南极部署一个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）通过跟踪亚暴演变过程中作为时间函数的爆发到达方位角，识别与MF爆发相关的亚暴扩展特征;（2）通过比较超低频和光学数据以及MF爆发的时间，比较和验证确定亚暴爆发的不同方法;（3）分析多波长光学和成像仪数据以确定引起MF爆发的极光电子谱的特征;（4）利用垂直交叉天线的数字数据和偏振的旋向性确定了MF爆发和极光嘶嘶声发射之间的详细关系在一些实施例中，MF突发事件在1500 kHz以下延伸的频率范围（指示传播模式）。前两个实验将有助于为亚暴研究发现新的实验方法，其余的实验将侧重于确定MF爆发的源机制及其与其他无线电发射的关系。这些实验将为理论工作者提供重要的实验材料，以显着提高我们对极光射电发射及其与各种极光现象宏观物理学关系的认识。

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..