Energetic Electron Precipitation: Multievent Analysis of Its Spatial Extent During EMIC Wave Activity
Energetic Electron Precipitation: Multievent Analysis of Its Spatial Extent During EMIC Wave Activity
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DOI：
10.1029/2018ja026291
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发表时间：
2019-04
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通讯作者：
L. Capannolo;Wen Li;Qianli Ma;Xiao‐Chen Shen;Xiao‐jia Zhang;R. Redmon;Juan V. Rodriguez;M. Engebretson;C. Kletzing;W. Kurth;G. Hospodarsky;H. Spence;G. Reeves;T. Raita
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作者：
L. Capannolo;Wen Li;Qianli Ma;Xiao‐Chen Shen;Xiao‐jia Zhang;R. Redmon;Juan V. Rodriguez;M. Engebretson;C. Kletzing;W. Kurth;G. Hospodarsky;H. Spence;G. Reeves;T. Raita
电磁离子回旋加速器(EMIC)波可以驱动数十keV质子和相对论电子的沉淀，是引起辐射带磁通丢失的潜在候选者。在这项研究中，我们对多颗低地球轨道(LEO)极地作业环境卫星/气象学作业卫星(POES/MetOp)观测到的三个EMIC驱动的降水个例进行了定量分析。在EMIC波活动期间，质子沉淀发生在几十keV到数百keV之间，而电子沉淀主要发生在相对论能量。我们将电子沉淀的观测结果与准线性理论的计算结果进行了比较。在所有情况下，我们考虑了与EMIC波同时观测到的其他磁层波的影响，即等离子体层嘶嘶和磁声波，发现MeV能量下的电子沉淀主要是由EMIC驱动的俯仰角散射引起的。有趣的是，LEO卫星观测到的每一次降水事件都延伸到一个有限的L壳区(平均ΔL~0.3)，这表明电磁波引起的俯仰角散射只在有利条件满足时才发生，可能发生在局部区域。此外，我们利用LEO星座，结合赤道附近(Van Allen探测器探测到的)或地面(磁强计测量到的)EMIC波观测，探索了不同的L壳层和磁本地时间扇区的降水发生情况。我们的分析表明，虽然EMIC波只在一个较窄的ΔL中驱动降水，但正如POES/MetOp所确定的那样，电子降水在一个相当宽的区域(高达~4.4hMLT和~1.4h L壳层)触发了不同的位置，卫星之间的模式相似。
Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of tens of keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this study, we quantitatively analyze three cases of EMIC‐driven precipitation, which occurred near the dusk sector observed by multiple Low‐Earth‐Orbiting (LEO) Polar Operational Environmental Satellites/Meteorological Operational satellite programme (POES/MetOp) satellites. During EMIC wave activity, the proton precipitation occurred from few tens of keV up to hundreds of keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi‐linear theory. For all cases, we consider the effects of other magnetospheric waves observed simultaneously with EMIC waves, namely, plasmaspheric hiss and magnetosonic waves, and find that the electron precipitation at MeV energies was predominantly caused by EMIC‐driven pitch angle scattering. Interestingly, each precipitation event observed by a LEO satellite extended over a limited L shell region (ΔL ~ 0.3 on average), suggesting that the pitch angle scattering caused by EMIC waves occurs only when favorable conditions are met, likely in a localized region. Furthermore, we take advantage of the LEO constellation to explore the occurrence of precipitation at different L shells and magnetic local time sectors, simultaneously with EMIC wave observations near the equator (detected by Van Allen Probes) or at the ground (measured by magnetometers). Our analysis shows that although EMIC waves drove precipitation only in a narrow ΔL, electron precipitation was triggered at various locations as identified by POES/MetOp over a rather broad region (up to ~4.4 hr MLT and ~1.4 L shells) with similar patterns between satellites.