Modulation of Electromagnetic Ion Cyclotron Waves by Pc5 ULF Waves and Energetic Ring Current Ions
Modulation of Electromagnetic Ion Cyclotron Waves by Pc5 ULF Waves and Energetic Ring Current Ions
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DOI：
10.1029/2017ja024930
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发表时间：
2019-03
期刊：
影响因子：
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通讯作者：
A. Kakad;B. Kakad;Y. Omura;A. K. Sinha;Aditi Upadhyay;R. Rawat
中科院分区：
文献类型：
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作者：
A. Kakad;B. Kakad;Y. Omura;A. K. Sinha;Aditi Upadhyay;R. Rawat
本文介绍了在印度南极Maitri站对强电磁离子回旋（EMIC）波的短周期和长周期调制的地面观测。这些波的特征在2011年9月17日（一个中等扰动的日子）4.7-7.2 UT间隔期间由感应线圈磁力计记录的磁场变化中是明显的。在这些波之前，太阳风动压逐渐增加，从3.88 UT开始。在Pc 1频段（0.5-0.9 Hz）观察到离散的升调EMIC波。对观测到的波谱图的周期性的研究表明，存在短周期（约2.4分钟）和长周期（约39-69分钟）。我们的分析表明，短周期与磁场线振荡产生的Pc 5超低频（ULF）波，而长周期可能与环电流漂移离子。采用一种基于互相关技术的新方法来确定离散上升音的扫描速率。平均扫描率估计在0.44-1.9 mHz/s的范围内是相对较低的扫描率相比，从卫星观测的EMIC波的过去的报告。我们发现，较高的扫描速率与地面上较强的EMIC波有关，这与理论研究一致。这表明理论上提出的扫描速率对生成区域中EMIC波强度的依赖性即使在这些波传播到地面期间也被保留。
We present a ground observation of modulations of strong electromagnetic ion cyclotron (EMIC) waves by short and long periodicities at Indian Antarctic station, Maitri. The signatures of these waves were evident in the magnetic field variations recorded by an induction coil magnetometer during the interval 4.7–7.2 UT on 17 September 2011, a moderately disturbed day. These waves were preceded by a gradual increase in the solar wind dynamic pressure, which started at 3.88 UT. The discrete rising tone EMIC waves were observed in the Pc1 frequency band (∼0.5–0.9 Hz). The investigation of the periodicities of the observed wave spectrogram shows the presence of short (≈2.4 min) and long (≈39–69 min) periodicities. Our analysis shows that the short periodicities are associated with the Pc5 Ultra Low Frequency (ULF) waves generated by magnetic field line oscillations, while long periodicities might be associated with the ring current drifting ions. A new method, based on the cross‐correlation technique, is adopted to determine sweep rates of the discrete rising tones. The average sweep rates estimated in the range of 0.44–1.9 mHz/s are relatively low as compared to the past reports of sweep rates derived from the satellite observations of EMIC waves. We found that the higher sweep rates are associated with the stronger EMIC waves on the ground, which is in agreement with the theoretical studies. This suggests that the theoretically proposed dependence of sweep rate on strength of EMIC wave in the generation region is retained even during the propagation of these waves to the ground.