Statistical study of auroral roar emissions observed at South Pole Station
Statistical study of auroral roar emissions observed at South Pole Station
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南极站观测到的极光轰鸣发射统计研究
DOI：
10.1029/2001ja000319
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发表时间：
2002
影响因子：
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通讯作者：
A. Weatherwax
中科院分区：
文献类型：
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作者：
J. Labelle;A. Weatherwax
[1]极光咆哮是在极光地带地面观测到的一种频带受限的自然极光射电发射，频率接近3兆赫和4.5兆赫，接近电子回转频率的2倍和3倍。使用半自动数据分析技术，我们生成了1999年在南极站(74°不变纬度)观测到的极光咆哮发射的频率、幅度和世界时间的数据库。这些数据证实，只有在电离层不被照射的时候，才能在地面观测到极光咆哮发射，而磁当地时间在控制在地面观测到的极光咆哮发射的发生率方面发挥着重要作用。在地磁活动较强的时期，极光咆哮的发生率和极光咆哮的幅度和频率范围增大。对于大幅度事件，极光咆哮频率的分布是双峰的，我们将其解释为证据，表明在地面观察到的极光咆哮发射的很大一部分来自顶部电离层。最后，从磁力计和甚低频数据推断的极光咆哮相对于亚暴起点的叠加纪元分析表明，极光咆哮发射有利地发生在这种事件之前，而不是发生在它们之后，这与以前的个案研究和轶事证据是一致的。
[1] Auroral roar is a band-limited natural auroral radio emission observed at ground level in the auroral zone at frequencies near 3 MHz and 4.5 MHz, close to 2 and 3 times the electron gyrofrequency. Using semiautomated data analysis techniques, we generate a database of frequencies, amplitudes, and universal times of 2fce-auroral roar emissions observed at South Pole Station (74° invariant latitude) during 1999. These data confirm that auroral roar emissions are observed at ground level only during times when the ionosphere is not illuminated, and magnetic local time plays a significant role in controlling the occurrence rates of auroral roar emissions observed at ground level. Auroral roar occurrence rates and the ranges of auroral roar amplitudes and frequencies increase during times of high geomagnetic activity. The distribution of auroral roar frequencies is bimodal for large-amplitude events, which we interpret as evidence that a substantial fraction of the auroral roar emissions observed at ground level originate in the topside ionosphere. Finally, superposed epoch analyses of occurrences of auroral roar relative to substorm onsets inferred from magnetometer and VLF data show that auroral roar emissions occur favorably preceding such events rather than after them, consistent with previous case study and anecdotal evidence.