H+, He+, He++, O++, N+ EMIC Wave Occurrence and Its Dependence on Geomagnetic Conditions: Results From 7 Years of Van Allen Probes Observations

IF 2.6 2区 地球科学 Q2 ASTRONOMY & ASTROPHYSICS
M. E. Usanova, L. A. Woodger, L. W. Blum, R. E. Ergun, C. Girard, D. L. Gallagher, R. M. Millan, J. G. Sample, A. T. Johnson, I. R. Mann
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Abstract

Electromagnetic ion cyclotron (EMIC) waves are believed to play an important role in the dynamics of the inner magnetosphere, including the ring current, the radiation belts and potentially, the cold plasma. In this work, we investigate their occurrence in the magnetosphere and the geomagnetic and solar wind conditions which lead to their excitation. We use an automated detection algorithm of EMIC waves observed by Van Allen Probes over the entire mission duration between 2012 and 2019. Consistent with earlier studies, we find that the H+ band occurrence maximizes in the dayside magnetosphere during enhancements of solar wind dynamic pressure. Both the H+ and He+ band are also generated along the duskside magnetosphere during disturbed geomagnetic conditions. In addition, to H+ and He+ bands commonly surveyed, we investigate the occurrence of H+ waves above and below 0.5 H+ gyrofrequency, as well as wave occurrence in the N+ and O++ bands. Most H+ waves are observed in the band below 0.5fH+. We find several events in the N+ band, indicative of their very low occurrence. The O++ band is observed during disturbed geomagnetic conditions and high solar wind dynamic pressure at low L-shells. Its radial localization coincides with the O++ torus. This study provides a comprehensive picture of EMIC wave distribution and insight into ion composition in the inner magnetosphere during variable geomagnetic conditions.

H+、He+、He++、O++、N+电磁波的发生及其与地磁条件的关系:范艾伦探测器 7 年的观测结果
电磁离子回旋波(EMIC)被认为在内部磁层(包括环流、辐射带和潜在的冷等离子体)的动力学中发挥着重要作用。在这项工作中,我们研究了它们在磁层中的发生以及导致其激发的地磁和太阳风条件。我们使用一种自动检测算法,对范艾伦探测器在 2012 年至 2019 年整个任务期间观测到的电磁波进行检测。与之前的研究一致,我们发现在太阳风动压增强时,H+波段在日侧磁层的出现率最大。在地磁扰动条件下,H+和He+波段也会沿黄昏侧磁层产生。除了常见的 H+ 和 He+ 波段,我们还研究了 0.5 H+ 陀螺频率上下的 H+ 波段,以及 N+ 和 O++ 波段中的波段。大多数 H+ 波是在 0.5fH+ 以下波段观测到的。我们在 N+ 波段发现了几个事件,表明其发生率非常低。O++波段是在地磁扰动和低L壳高太阳风动压条件下观测到的。它的径向定位与 O++ 磁环相吻合。这项研究提供了 EMIC 波分布的全面图景,并有助于深入了解多变地磁条件下内磁层的离子组成。
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来源期刊
Journal of Geophysical Research: Space Physics
Journal of Geophysical Research: Space Physics Earth and Planetary Sciences-Geophysics
CiteScore
5.30
自引率
35.70%
发文量
570
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