Statistical study of selective oxygen increase in high‐energy ring current ions during magnetic storms
Statistical study of selective oxygen increase in high‐energy ring current ions during magnetic storms
复制标题
磁暴期间高能环流离子选择性增氧的统计研究
DOI：
10.1029/2018ja026168
复制
发表时间：
2019
期刊：
影响因子：
--
通讯作者：
and Y. Obana
中科院分区：
文献类型：
--
作者：
Mitani;K.;K. Seki;K. Keika;M. Gkioulidou;L. J. Lanzerotti;D. G. Mitchell;C. A. Kletzing;A. Yoshikawa;and Y. Obana
离子从等离子体片向环电流的输运是环电流发展的主要原因。高能（>150 keV）环电流离子已知在几天内扩散传输。最近的一项研究表明，由于在2013年4月24日磁暴期间由漂移和漂移反弹共振与Pc 3-5超低频波的组合引起的扩散传输，高能氧离子比质子更接近地球。为了了解这种选择性氧增加（SOI）的发生条件，我们利用货车艾伦探测器上的辐射带风暴探针离子成分实验装置，在2013-2017年90次磁暴期间，在L ~ 3-6测量了质子和氧离子之间的相空间密度（PSD），第一绝热不变量（μ）为0.1-2.0 keV/nT。我们确定了SOI事件，其中氧PSD增加，而质子PSD不增加在9小时（一个轨道周期）期间。在90次磁暴中，33%的磁暴伴随SOI事件。在SOI事件期间，地面磁力计观测到的Pc 4和Pc 5波的全球增强表明，由于漂移反弹共振与Pc 4振荡和漂移共振与Pc 5振荡的组合而导致的径向传输可能是SOI的原因。SOI事件对磁暴强度的贡献平均约为9%。
Ion transport from the plasma sheet to the ring current is the main cause of the development of the ring current. Energetic (>150 keV) ring current ions are known to be transported diffusively in several days. A recent study suggested that energetic oxygen ions are transported closer to the Earth than protons due to the diffusive transport caused by a combination of the drift and drift‐bounce resonances with Pc 3–5 ultralow frequency waves during the 24 April 2013 magnetic storm. To understand the occurrence conditions of such selective oxygen increase (SOI), we investigate the phase space densities (PSDs) between protons and oxygen ions with the first adiabatic invariants (μ) of 0.1–2.0 keV/nT measured by the Radiation Belt Storm Probes Ion Composition Experiment instrument on the Van Allen Probes atL~ 3–6 during 90 magnetic storms in 2013–2017. We identified the SOI events in which oxygen PSDs increase while proton PSDs do not increase during a period of ~9 hr (one orbital period). Among the 90 magnetic storms, 33% were accompanied by the SOI events. Global enhancements of Pc 4 and Pc 5 waves observed by ground magnetometers during the SOI events suggest that radial transport due to combination of the drift‐bounce resonance with Pc 4 oscillations and the drift resonance with Pc 5 oscillations can be the cause of SOIs. The contribution of the SOI events to the magnetic storm intensity is roughly estimated to be ~9% on average.