Electric and magnetic field observations of Pc4 and Pc5 pulsations in the inner magnetosphere: A statistical study
Electric and magnetic field observations of Pc4 and Pc5 pulsations in the inner magnetosphere: A statistical study
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DOI：
10.1029/2009ja014243
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发表时间：
2009-12
影响因子：
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通讯作者：
Wenlong Liu;T. Sarris;Xinlin Li;S. Elkington;R. Ergun;V. Angelopoulos;J. Bonnell;K. Glassmeier
中科院分区：
文献类型：
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作者：
Wenlong Liu;T. Sarris;Xinlin Li;S. Elkington;R. Ergun;V. Angelopoulos;J. Bonnell;K. Glassmeier
[1]Pc 4和Pc 5波段的超低频（ULF）波在内磁层中普遍存在，对高能粒子输运有重要影响。研究超低频波的来源和特征也有助于我们更好地理解太阳风与磁层之间的相互作用过程。然而，由于仪器和空间覆盖的限制，ULF波在当地时间和L壳层内磁层的分布还没有得到完全的研究。最近的亚暴期间事件和大尺度相互作用的时间历史（THEMIS）使命提供了独特的机会，以调查不同的L壳层的超低频脉动的空间分布，在太阳极小期内，在磁层内具有完整的当地时间覆盖范围，同时进行电场和磁场测量。Pc 4和Pc 5脉动的电场观测确定整个13个月的测量，覆盖当地时间24小时。脉动的特点是作为环形或极向（包括压缩）模式，这取决于电场的极化。记录了脉动的发生率和波功率在径向距离和当地时间上的分布。而Pc 4和Pc 5事件的分布随径向距离和当地时间的变化很大，Pc 4事件更频繁地在5-6 RE附近的内部区域观察到，Pc 5事件更频繁地在7-9 RE附近的外部区域观察到，这表明场线共振是ULF波的重要来源。在侧翼区域，波功率主要是由环形模式，可能与开尔文-亥姆霍兹（KH）不稳定性。在中午部分，Pc 5超低频波功率主要由极向模态控制，可能与太阳风动压扰动有关。我们的观测表明，KH不稳定性在太阳风动压相对较弱的太阳活动极小期起着重要作用。我们还发现，贡献的Pc 5超低频波功率从外部源大于从内部源的贡献。这些统计结果在描述Pc 4和Pc 5波的特性方面是重要的，并且对于模拟高能粒子在磁层中的传输的任何努力也是重要的。
[1] Ultralow frequency (ULF) waves in the Pc4 and Pc5 bands are ubiquitous in the inner magnetosphere and have significant influence on energetic particle transport. Investigating the source and characteristics of ULF waves also helps us better understand the interaction processes between the solar wind and the magnetosphere. However, owing to the limitation in instrumentation and spatial coverage, the distribution of ULF waves in local time and L shell in the inner magnetosphere has not been completely studied. The recent Time History of Events and Macroscale Interactions During Substorms (THEMIS) mission provides unique opportunities to investigate the spatial distribution of ULF pulsations across different L shells with full local time coverage in the inner magnetosphere during solar minimum, with both electric and magnetic field measurements. Pc4 and Pc5 pulsations in the electric field observations are identified throughout 13 months of measurements, covering 24 h in local time. The pulsations are characterized as either toroidal or poloidal (including compressional) mode, depending on the polarization of the electric field. Subsequently, the pulsations' occurrence rate and wave power distributions in radial distance and local time are recorded. While the distributions of both Pc4 and Pc5 events vary greatly with radial distance and local time, Pc4 events are more frequently observed in the inner region around 5–6 RE and Pc5 events are more frequently observed in the outer region around 7–9 RE, which suggests that the field line resonance is an important source of the ULF waves. In the flank regions, the wave power is dominated by the toroidal mode, likely associated with the Kelvin-Helmholtz (KH) instability. In the noon sector, the Pc5 ULF wave power is dominated by the poloidal mode, likely associated with the solar wind dynamic pressure disturbance. The KH instability plays an important role, suggested by our observations, during the solar minimum when the solar wind dynamic pressure is relatively weak. We also find that the contributions to the Pc5 ULF wave power from the external sources are larger than the contributions from the internal sources. These statistical results are important in characterizing Pc4 and Pc5 waves and also important for any efforts to model the transport of energetic particles in the magnetosphere.