Daytime high‐latitude auroral pulsations: Some morphological features and the region of the magnetospheric source
Daytime high‐latitude auroral pulsations: Some morphological features and the region of the magnetospheric source
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白天高纬度极光脉动：一些形态特征和磁层源区域
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
P. Newell
中科院分区：
文献类型：
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作者：
V. Vorobjev;O. Yagodkina;D. Sibeck;P. Newell
我们提出了在尖点和裂隙纬度处观察到的极光脉动作为太阳风和地磁条件函数的统计研究结果。脉动周期范围为 10 至 40 秒，但可通过 3 至 5 分钟的较长周期变化进行调制。极光脉动通常伴随着地磁脉动，几乎每天都会发生，而极光脉动只能在所研究的所有天数的 20% 至 30% 中看到。极光脉动显示出在地磁安静时期发生的明显趋势，此时行星际磁场（IMF）具有向黎明和向北或仅稍微向南的分量。极光脉动在地磁纬度 74°–75° 0800 到 1100 MLT 期间最常见。短周期脉动的纬向范围为数十秒至一百公里，纵向范围为数百公里。极光脉动没有表现出在太阳风速度或密度增强的间隔期间或在近径向 IMF 方向的间隔期间发生的趋势。将脉动发生的纬度与低空 DMSP F7 和 NOAA 7 航天器的观测进行比较的案例和统计研究表明，脉动发生在磁层深处的闭合磁场线上，紧邻高纬度高能粒子捕获边界的赤道。因此，我们得出的结论是，它们不是由白天磁层顶的磁合并、开尔文-亥姆霍兹不稳定性或地球前震内产生的脉动通过磁鞘传输到磁层的结果。极光脉动的起源仍然未知，尽管最终可能用辐射带外缘的不稳定性来解释它们。
We present the results of a statistical study of auroral pulsations observed at cusp and cleft latitudes as a function of solar wind and geomagnetic conditions. Pulsation periods range from 10 to 40 s but are modulated by longer-period variations ranging from 3 to 5 min. The auroral pulsations are generally accompanied by geomagnetic pulsations, which occur almost every day, whereas the auroral pulsations can only be seen on 20 to 30% of all days studied. The auroral pulsations show a distinct tendency to occur during geomagnetically quiet periods when the interplanetary magnetic field (IMF) has dawnward and northward or only slightly southward components. The auroral pulsations are most common from 0800 to 1100 MLT at 74°–75° geomagnetic latitude. The shorter-period pulsations have latitudinal extents ranging from several 10 s to 100 km, and longitudinal extents of several hundred kilometers. The auroral pulsations show no tendency to occur during intervals of enhanced solar wind velocities or densities, or during intervals of near-radial IMF orientation. Case and statistical studies comparing the latitude at which the pulsations occur with observations by low-altitude DMSP F7 and NOAA 7 spacecraft demonstrate that they occur deep within the magnetosphere on closed magnetic field lines immediately equatorward of the high-latitude trapping boundary for energetic particles. Consequently, we conclude that they do not result from magnetic merging on the dayside magnetopause, the Kelvin-Helmholtz instability, or the transmission of pulsations generated within the Earth's foreshock through the magnetosheath and into the magnetosphere. The origin of the auroral pulsations remains unknown, although it may ultimately be possible to explain them in terms of instabilities at the outer edge of the radiation belt.