Combined scattering loss of radiation belt relativistic electrons by simultaneous three‐band EMIC waves: A case study
Combined scattering loss of radiation belt relativistic electrons by simultaneous three‐band EMIC waves: A case study
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DOI：
10.1002/2016ja022483
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发表时间：
2016-05
期刊：
影响因子：
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通讯作者：
Fengming He;Xing Cao;B. Ni;Z. Xiang;Chen Zhou;X. Gu;Zhengyu Zhao;R. Shi;Qi Wang
中科院分区：
文献类型：
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作者：
Fengming He;Xing Cao;B. Ni;Z. Xiang;Chen Zhou;X. Gu;Zhengyu Zhao;R. Shi;Qi Wang
多波段电磁离子回旋波可以有效地驱动辐射带相对论电子的散射损耗。然而，同时捕获EMIC波的三个频带在统计上是不常见的。利用数据从电场和磁场仪器套件和集成科学磁力计板载货车艾伦探针A，我们报告的同时存在的三个（H+，He+，和O+）的发射带的EMIC波事件，这提供了一个机会，看看所有的EMIC排放的组合散射效应和相对的作用，每个频带在扩散辐射带相对论电子在现实情况下。通过准线性扩散率计算和一维纯俯仰角扩散模拟获得的定量结果表明，同时三波段EMIC波的组合共振散射总体上由He+波段波扩散主导，这主要是由于其对波功率的主导作用。（H+、He+和O+波段的平均波幅分别约为0.4 nT、1.6 nT和0.15 nT）。在损失锥附近，2-3 MeV电子以10−6-10−5 s−1的速率进行俯仰角散射，而5-10 MeV电子可以以10−3-10−2 s−1的速率更有效地扩散，这接近强扩散水平，并导致大气损失的中等或重度填充的损失锥。相应的电子损失时间尺度（即，寿命）从~2 MeV能量下的几天到~10 MeV能量下的不到1小时不等。这个案例研究表明，在三个EMIC波段共存期间，He+波段波对辐射带相对论电子损失的主要贡献，并建议在未来的建模工作中应仔细考虑不同EMIC波段在相对论电子动力学中的作用。
Multiband electromagnetic ion cyclotron (EMIC) waves can drive efficient scattering loss of radiation belt relativistic electrons. However, it is statistically uncommon to capture the three bands of EMIC waves concurrently. Utilizing data from the Electric and Magnetic Field Instrument Suite and Integrated Science magnetometer onboard Van Allen Probe A, we report the simultaneous presence of three (H+, He+, and O+) emission bands in an EMIC wave event, which provides an opportunity to look into the combined scattering effect of all EMIC emissions and the relative roles of each band in diffusing radiation belt relativistic electrons under realistic circumstances. Our quantitative results, obtained by quasi‐linear diffusion rate computations and 1‐D pure pitch angle diffusion simulations, demonstrate that the combined resonant scattering by the simultaneous three‐band EMIC waves is overall dominated by He+ band wave diffusion, mainly due to its dominance over the wave power (the mean wave amplitudes are approximately 0.4 nT, 1.6 nT, and 0.15 nT for H+, He+, and O+ bands, respectively). Near the loss cone, while 2–3 MeV electrons undergo pitch angle scattering at a rate of the order of 10−6–10−5 s−1, 5–10 MeV electrons can be diffused more efficiently at a rate of the order of 10−3–10−2 s−1, which approaches the strong diffusion level and results in a moderately or heavily filled loss cone for the atmospheric loss. The corresponding electron loss timescales (i.e., lifetimes) vary from several days at the energies of ~2 MeV to less than 1 h at ~10 MeV. This case study indicates the leading contribution of He+ band waves to radiation belt relativistic electron losses during the coexistence of three EMIC wave bands and suggests that the roles of different EMIC wave bands in the relativistic electron dynamics should be carefully incorporated in future modeling efforts.