A large survey of electron acceleration events
A large survey of electron acceleration events
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DOI：
10.1029/95ja03147
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发表时间：
1996-02
影响因子：
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通讯作者：
P. Newell;K. Lyons;C. Meng
中科院分区：
文献类型：
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作者：
P. Newell;K. Lyons;C. Meng
对所有国防气象卫星计划 (DMSP) 卫星在 9 年时间间隔内的降水数据进行了电子加速事件调查。选定的事件显示光谱峰值急剧下降；因此，仅研究加速势比源热能大 3-4 倍或更多的情况。总之，我们检查了超过 1.5 × 108 个单独的电子能谱，以寻找这种巨大的场对准加速的迹象。这项调查可以解决一些争议；例如，“中午间隙”是真实存在的，中午很可能是观测电子加速的最不可能的当地时间。有争议的“14 MLT（磁当地时间）热点”也是真实存在的，尽管它以 15 MLT 为中心，并且仅在向北的行星际磁场 (IMF) 条件下与椭圆形的其余部分不同。 6-9 MLT 区域存在较弱的“暖”点。从统计上看，大约 3 keV 及以上的潜在下降属于夜侧范围，最强烈的能量通量 (>1 erg cm−2 s−1) 也是如此。加速度事件的纬度尺度大小与特征宽度（= 28-35 km）的指数分布非常吻合，该特征宽度仅随 MLT 和 IMF 条件略有变化。如果代表驱动磁层过程的电离层足迹，则最佳候选解释是主等离子体片中的速度剪切。然而，在各种条件下存在纬度宽度指数分布的事实表明了另一种选择。如果存在嵌入极光椭圆形内的大尺度区域，其中每个光谱具有独立于相邻光谱的经历电子加速的随机概率P，则可以解释出现分布，并且实际上指示P的值（即～0.85）。
Precipitation data from all Defense Meteorological Satellite Program (DMSP) satellites over a 9-year interval were surveyed for electron acceleration events. Selected events evinced a sharp drop above the spectral peak; therefore only instances where the accelerating potential is 3–4 or more times larger than the source thermal energy were studied. In all, more than 1.5 × 108 individual electron spectra were examined for signs of such substantial field-aligned acceleration. Several controversies can be resolved by this survey; for example, the “midday gap” is real, with noon easily the least likely local time for observing electron acceleration. The debated “14 MLT (magnetic local time) hot spot” is also real, although it is centered about 15 MLT and is distinct from the rest of the oval only for northward interplanetary magnetic field (IMF) conditions. A weaker “warm” spot exists in the 6–9 MLT region. Potential drops of ∼3 keV and above are statistically the province of the nightside, as are the most intense energy fluxes (>1 erg cm−2 s−1). The latitudinal scale size of acceleration events fits surprisingly well to an exponential distribution with a characteristic width ( = 28–35 km) that varies only slightly with MLT and IMF conditions. If represents the ionospheric footprint of the driving magnetospheric processes, the best candidate explanation is velocity shears in the main plasma sheet. However, the fact that an exponential distribution of latitudinal widths exists under a variety of conditions suggests an alternative. If there exist large-scale regions embedded within the auroral oval wherein each spectrum has a random probability P of experiencing electron acceleration independent of neighboring spectra, then the occurrence distributions are explained, and actually indicates the value of P (namely, ∼0.85).