Ion-scale Electromagnetic Waves in the Inner Heliosphere
Ion-scale Electromagnetic Waves in the Inner Heliosphere
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DOI：
10.3847/1538-4365/ab6c65
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发表时间：
2019-12
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影响因子：
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通讯作者：
T. Bowen;A. Mallet;Jia Huang;K. Klein;D. Malaspina;M. Stevens;S. Bale;J. Bonnell;A. Case-A.-Cas
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文献类型：
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作者：
T. Bowen;A. Mallet;Jia Huang;K. Klein;D. Malaspina;M. Stevens;S. Bale;J. Bonnell;A. Case-A.-Cas
了解太阳风和日冕中积极促进加热、加速和耗散的物理过程是 NASA 帕克太阳探测器 (PSP) 任务的主要目标。对离子尺度圆偏振电磁波的观测表明，回旋共振和波粒相互作用在日光层内部是动态相关的。对 PSP 第一次近日点遭遇中圆偏振事件的基于小波的统计研究表明，在 30-50% 的径向场间隔中观察到离子共振尺度的横向电磁波。测量到的平均波幅约为 4 nT，而波事件的平均持续时间约为 20 秒；然而，持续时间较长的波浪事件可以在长达一小时的时间尺度上不间断地存在。波矢量的确定表明传播平行于/反平行于平均磁场。虽然离子尺度波在径向平均磁场的间隔期间优先被观测到，但我们表明，与单航天器采样与各向异性湍流叠加的准平行波相关的测量限制，使得当平均磁场与太阳风流倾斜时测得的相干离子波谱不可观测；这些结果意味着相干离子尺度波的发生并不限于径向场配置。特征波振幅和持续时间缺乏径向缩放表明波是通过等离子体不稳定性就地产生的。此外，对质子分布函数的观察表明，温度各向异性可能驱动观察到的离子尺度波。
Understanding the physical processes in the solar wind and corona that actively contribute to heating, acceleration, and dissipation is a primary objective of NASA’s Parker Solar Probe (PSP) mission. Observations of circularly polarized electromagnetic waves at ion scales suggest that cyclotron resonance and wave–particle interactions are dynamically relevant in the inner heliosphere. A wavelet-based statistical study of circularly polarized events in the first perihelion encounter of PSP demonstrates that transverse electromagnetic waves at ion resonant scales are observed in 30–50% of radial field intervals. Average wave amplitudes of approximately 4 nT are measured, while the mean duration of wave events is on the order of 20 s; however, long-duration wave events can exist without interruption on hour-long timescales. Determination of wave vectors suggests propagation parallel/antiparallel to the mean magnetic field. Though ion-scale waves are preferentially observed during intervals with a radial mean magnetic field, we show that measurement constraints, associated with single spacecraft sampling of quasi-parallel waves superposed with anisotropic turbulence, render the measured coherent ion-wave spectrum unobservable when the mean magnetic field is oblique to the solar wind flow; these results imply that the occurrence of coherent ion-scale waves is not limited to a radial field configuration. The lack of radial scaling of characteristic wave amplitudes and duration suggests that the waves are generated in situ through plasma instabilities. Additionally, observations of proton distribution functions indicate that temperature anisotropy may drive the observed ion-scale waves.