Energization of radiation belt electrons by ring current ion driven ULF waves
Energization of radiation belt electrons by ring current ion driven ULF waves
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DOI：
10.1029/2007ja012468
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发表时间：
2008-02
影响因子：
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通讯作者：
L. Ozeke;I. Mann
中科院分区：
文献类型：
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作者：
L. Ozeke;I. Mann
[1] 在本文中，我们研究了 MeV 能量辐射带电子可以被 ULF 波激发的假设，ULF 波本身被高能环流离子的漂移弹跳共振激发。我们表明，这种激励最有可能发生在耗尽等离子体槽条件下以及等离子体层顶位于低 L 壳层上时。例如，当等离子体层被侵蚀，使得等离子体层顶位于 L = 3 时，则 N = 2 漂移弹跳共振产生的 ULF 波可以分别与 ≃ 10–15 keV H+ 或 ≃ 100–300 keV O+ 环流离子产生 ULF 波，从而在 L ≃ 3–4 时对能量 >1 MeV 的电子进行有效激发。我们通过考虑具有基本场对准模式 m ≃ +20 引导的极向阿尔文波的辐射带电子漂移共振来说明从环流到辐射带的能量转移，该波由向西漂移的环流离子激发。我们的结果具有重要意义，因为它们为 MeV 辐射带电子的 ULF 波供能提供了新的范例，表明环流离子驱动的 ULF 波可能在 ULF 波的辐射带供能中发挥重要作用。考虑到风暴期间L~3-4环电流中~100 keV O+离子的普遍存在，以及风暴期间等离子体层顶的侵蚀，在风暴期间将满足从环电流到辐射带中>1 MeV电子的高效ULF波能量转移所需的条件。
[1] In this paper we examine the hypothesis that MeV energy radiation belt electrons can be energized by ULF waves, the ULF waves themselves being excited by drift-bounce resonance with energetic ring current ions. We show that this energization is most likely to occur during depleted plasmatrough conditions and when the plasmapause lies on a low L-shell. For example, when the plasmasphere has been eroded so that the plasmapause lies at L = 3, then efficient energization for electrons with energies >1 MeV at L ≃ 3–4 can be caused by ULF waves generated by the N = 2 drift-bounce resonance with either ≃ 10–15 keV H+, or ≃ 100–300 keV O+, ring current ions respectively. We illustrate this transfer of energy from the ring current to the radiation belt by considering a radiation belt electron drift resonance with fundamental field-aligned mode m ≃ +20 guided poloidal Alfven waves, the waves being excited by westward drifting ring current ions. Our results are significant in that they offer a new paradigm for the ULF wave energization of MeV radiation belt electrons, suggesting that ring current ion driven ULF waves may play an important role in radiation belt energization by ULF waves. Given the prevalence of ∼100 keV O+ ions in the ring current at L ∼ 3–4 during storm-times, and the storm-time erosion of the plasmapause, the conditions required for efficient ULF wave energy transfer from the ring current to >1 MeV electrons in the radiation belt will be satisfied during storm-times.