Fast‐moving diffuse auroral patches: A new aspect of daytime Pc3 auroral pulsations
Fast‐moving diffuse auroral patches: A new aspect of daytime Pc3 auroral pulsations
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DOI：
10.1002/2016ja023285
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发表时间：
2017-02
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影响因子：
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通讯作者：
T. Motoba;Y. Ebihara;A. Kadokura;M. Engebretson;M. Lessard;A. Weatherwax;A. Gerrard
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文献类型：
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作者：
T. Motoba;Y. Ebihara;A. Kadokura;M. Engebretson;M. Lessard;A. Weatherwax;A. Gerrard
极光脉动是磁层中波粒相互作用的便捷诊断。本文介绍了 2012 年 5 月 17 日在南极站（南磁纬度 74.4°）使用 ~2 Hz 采样全天相机测量的白天 Pc3（22-100 mHz）极光脉动事件的案例研究。白天 Pc3 极光脉动在闭合场线区域最活跃，该区域极光以弥漫性绿线发射为主，且在当地正午磁力±2 小时内。通常（但并非总是如此），相应的周期性变化是用同一位置的搜索线圈磁力计记录的。特别令人感兴趣的是二维极光特征，表明给定点的时间光度变化是由于规模约为 100 公里的微弱、非脉动极光斑块的重复形成和水平运动造成的。各个斑块以 15 km s−1 至 20–25 km s−1 的速度沿着磁子午线通过当地磁天顶依次向赤道传播。这些特性与典型的脉动极光有很大不同，是特定极光斑块中的周期性开关光度变化，并根据磁层中的对流电场进行漂移。我们推测，快速移动的极光斑块的这种重复模式是白天 Pc3 极光脉动的另一个方面，可能是压缩 Pc3 波的可见表现，它向地球传播并引起白天外磁层中沉淀 keV 电子通量的调制。
Auroral pulsations are a convenient diagnostic of wave‐particle interactions in the magnetosphere. A case study of a daytime Pc3 (22–100 mHz) auroral pulsation event, measured with a ~2 Hz sampling all‐sky camera at South Pole Station (74.4°S magnetic latitude) on 17 May 2012, is presented. The daytime Pc3 auroral pulsations were most active in a closed field line region where the aurora was dominated by diffuse green‐line emissions and within ±2 h of magnetic local noon. Usually, but not always, the corresponding periodic variations were recorded with a colocated search coil magnetometer. Of particular interest is the two‐dimensional auroral signature, indicating that the temporal luminosity variations at a given point were due to repeated formation and horizontal motion of faint, nonpulsating auroral patches with scale sizes of ~100 km. The individual patches propagated equatorward with speeds of 15 km s−1 up to 20–25 km s−1 one after another along the magnetic meridian through local magnetic zenith. These properties differ considerably from typical pulsating aurorae, being periodic on‐off luminosity variations in a particular auroral patch and drifting in accordance with the convection electric field in the magnetosphere. We speculate that such repetitive patterns of the fast‐moving auroral patches, being another aspect of the daytime Pc3 auroral pulsations, may be a visible manifestation of compressional Pc3 waves which propagate earthward and cause modulation of precipitating keV electron fluxes in the dayside outer magnetosphere.