Xiao Fuliang, Yang Chang, Su Zhenpeng, Zhou Qinghua, He Zhaoguo, He Yihua, Baker D N, Spence H E, Funsten H O, Blake J B
School of Physics and Electronic Sciences, Changsha University of Science and Technology, 2nd Section, South Wanjiali Road #960, Yuhua District, Changsha, Hunan 410004, China.
Chinese Academy of Sciences Key Laboratory for Basic Plasma Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
Nat Commun. 2015 Oct 5;6:8590. doi: 10.1038/ncomms9590.
Van Allen radiation belts consist of relativistic electrons trapped by Earth's magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90° further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day-night asymmetry in Earth's magnetic field. However, direct observation of a butterfly distribution well inside of geostationary orbit and the origin of this phenomenon have not been provided so far. Here we report high-resolution observation that a unusual butterfly pitch angle distribution of relativistic electrons occurred within 5 Earth radii during the 28 June 2013 geomagnetic storm. Simulation results show that combined acceleration by chorus and magnetosonic waves can successfully explain the electron flux evolution both in the energy and butterfly pitch angle distribution. The current provides a great support for the mechanism of wave-driven butterfly distribution of relativistic electrons.
范艾伦辐射带由被地球磁场捕获的相对论电子组成。被捕获的电子常常围绕地球做方位角漂移，并呈现出蝴蝶形俯仰角分布，其最小值出现在比地球同步轨道更远的90°处。这通常归因于地球磁场昼夜不对称导致的漂移壳层分裂。然而，到目前为止，尚未提供对地球同步轨道内蝴蝶分布的直接观测以及该现象的起源。在此，我们报告高分辨率观测结果，即在2013年6月28日的地磁暴期间，在5个地球半径范围内出现了相对论电子异常的蝴蝶形俯仰角分布。模拟结果表明，合声与磁声波的联合加速能够成功解释电子通量在能量和蝴蝶形俯仰角分布方面的演化。这一结果为相对论电子的波驱动蝴蝶分布机制提供了有力支持。
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