A statistical study of EMIC wave-associated He + energization in the outer magnetosphere: Cluster/CODIF observations
A statistical study of EMIC wave-associated He + energization in the outer magnetosphere: Cluster/CODIF observations
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DOI：
10.1029/2011ja016690
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发表时间：
2009-12
影响因子：
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通讯作者：
Jichun Zhang;L. Kistler;C. Mouikis;B. Klecker;J. Sauvaud;M. Dunlop
中科院分区：
文献类型：
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作者：
Jichun Zhang;L. Kistler;C. Mouikis;B. Klecker;J. Sauvaud;M. Dunlop
[1]在2001年3月1日至2008年4月1日期间，星团上的成分和分布函数（CODIF）分析仪观测到41个持续时间为1.10-4.97 h的He+ He事件，平均持续时间为3.18 ± 0.91 h。这些He+加热事件主要发生在外磁层（L = 7.9-14.6）下午区（MLT = 11：32-19：06）的低/中磁纬度（MLAT = −4.3°-51.7°）。在这些事件中，He+离子与电磁离子回旋（EMIC）波共振相互作用，并被垂直激励到高达1 keV的能量。在0.04-1 keV的能量范围内，它们对总离子密度的贡献平均提高到51%。在这些事件期间，对Cluster测量的等离子体数据进行叠加历元分析表明存在两个EMIC波控制因素：热各向异性H+（波自由能提供者）和冷稠密等离子体（波生成催化剂）。此外，它是常见的事件中，高能量的H+的密度升高和电子等离子体/陀螺频率比（fpe/fce）达到高于10的值。平静的太阳风和地磁活动似乎是产生EMIC波的有利条件，因此，在外磁层区域的合成的He+ Σ。原因是，在安静的太阳风和地磁条件下，来自等离子体片的热的各向异性H+和来自等离子体层羽或羽状区域的冷的致密等离子体的重叠可能存在于外磁层的下午部分。
[1] During the time period of 1 March 2001–1 April 2008, the Composition and Distribution Function (CODIF) Analyzer on board Cluster observed 41 prolonged He+ energization events, lasting for 1.10–4.97 h, on average, 3.18 ± 0.91 h. These He+ heating events occurred predominantly at low/middle magnetic latitudes (MLAT = −4.3°–51.7°) in the afternoon sector (MLT = 11:32–19:06) in the outer magnetosphere (L = 7.9–14.6). During the events, the He+ ions resonantly interacted with electromagnetic ion cyclotron (EMIC) waves and were perpendicularly energized to energies up to 1 keV. Their contribution to total ion density in the energy range of 0.04–1 keV was elevated on average up to 51%. A superposed epoch analysis of the plasma data measured by Cluster during these events indicates the presence of the two EMIC wave-controlling factors: hot anisotropic H+ (the wave free-energy provider) and cold dense plasma (the wave generation catalyst). In addition, it is common in the events that the density of the energetic H+ is elevated and electron plasma/gyrofrequency ratio (fpe/fce) reaches values higher than 10. Quiet solar wind and geomagnetic activity appear to be favorable conditions for the generation of the EMIC waves and thus the resultant He+ energization in the outer-magnetospheric region. The reason is that, under quiet solar wind and geomagnetic conditions, an overlap of hot anisotropic H+ from the plasma sheet and cold dense plasma from a plasmaspheric plume or plume-like region could exist in the afternoon sector of the outer magnetosphere.