The optical manifestation of dispersive field‐aligned bursts in auroral breakup arcs
The optical manifestation of dispersive field‐aligned bursts in auroral breakup arcs
复制标题
极光分裂弧中色散场对齐爆发的光学表现
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
M. Zettergren
中科院分区：
文献类型：
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作者：
H. Dahlgren;J. Semeter;R. Marshall;M. Zettergren
对亚暴膨胀的高分辨率光学观测显示，动态极光射线伴随着亮度的激增沿着磁力线向上传播。在地面成像仪中观察到的这种现象被称为极光火焰，而相应的能量分散的火箭特征更常被称为场对准爆发。在本文中，使用科学级互补金属氧化物半导体（CMOS）传感器（30° × 30°视场，120 km处30 m分辨率）以50帧/秒的速度获得的极光火焰观测结果用于深入了解沉淀电子的性质，类似于高分辨率粒子探测器。由于该系统的大视场和高空间分辨率，可以从单个传感器获得体积发射率高度的时间演变的一阶估计。测得的体积发射率进行了比较与模型化的本征轮廓的总和为一组有限的电子束与不同的能量所提供的TRANSCAR极光通量管模型。在几分之一秒的时间内，可以详细分析每条极光射线内的能量色散特征。降水能量和通量的演变表明，降水跨越了很大的能量范围，特征能量在0.2s内从2.1keV下降到0.87keV。磁天顶2.4赫兹的振荡对应于极光火焰的周期，加速被认为是由于阿尔文波与电离层上方的电子相互作用。
High‐resolution optical observations of a substorm expansion show dynamic auroral rays with surges of luminosity traveling up the magnetic field lines. Observed in ground‐based imagers, this phenomenon has been termed auroral flames, whereas the rocket signatures of the corresponding energy dispersions are more commonly known as field‐aligned bursts. In this paper, observations of auroral flames obtained at 50 frames/s with a scientific‐grade Complementary Metal Oxide Semiconductor (CMOS) sensor (30° × 30° field of view, 30 m resolution at 120 km) are used to provide insight into the nature of the precipitating electrons similar to high‐resolution particle detectors. Thanks to the large field of view and high spatial resolution of this system, it is possible to obtain a first‐order estimate of the temporal evolution in altitude of the volume emission rate from a single sensor. The measured volume emission rates are compared with the sum of modeled eigenprofiles obtained for a finite set of electron beams with varying energy provided by the TRANSCAR auroral flux tube model. The energy dispersion signatures within each auroral ray can be analyzed in detail during a fraction of a second. The evolution of energy and flux of the precipitation shows precipitation spanning over a large range of energies, with the characteristic energy dropping from 2.1 keV to 0.87 keV over 0.2 s. Oscillations at 2.4 Hz in the magnetic zenith correspond to the period of the auroral flames, and the acceleration is believed to be due to Alfvenic wave interaction with electrons above the ionosphere.