Giant Pulsations Excited by a Steep Earthward Gradient of Proton Phase Space Density: Arase Observation
Giant Pulsations Excited by a Steep Earthward Gradient of Proton Phase Space Density: Arase Observation
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DOI：
10.1029/2018gl078293
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发表时间：
2018-07
影响因子：
5.2
通讯作者：
Kazuhiro Yamamoto;M. Nosé;S. Kasahara;S. Yokota;K. Keika;A. Matsuoka;M. Teramoto;Kazue Takahashi
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文献类型：
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作者：
Kazuhiro Yamamoto;M. Nosé;S. Kasahara;S. Yokota;K. Keika;A. Matsuoka;M. Teramoto;Kazue Takahashi
我们目前的观测证据向西传播的奇模驻波超低频波和高能质子之间的漂移共振。2017年4月15日，Arase卫星在地磁当地时间2003小时探测到了13mHz（Pc4波段）的压缩波和大于50 keV的质子通量振荡。根据地面观测，方位波数（m数）估计为m −50，而漂移共振理论给出的奇模波和110 keV质子的m − 49，提供了漂移共振确实发生在这一事件中的证据。我们还发现质子相空间密度向地球方向存在陡峭的梯度，这可以定量解释波的激发。观测到的波显示了巨脉动（PGS）的典型特征，关于当地时间，m数和通量振荡。因此，本研究对Pgs的场线模式结构和激发机制具有重要意义。
We present observational evidence of drift resonance between westward propagating odd mode standing ultralow frequency waves and energetic protons. Compressional ∼13 mHz (Pc4 band) waves and proton flux oscillations at >50 keV were detected at ∼03 hr magnetic local time by the Arase satellite on 15 April 2017. The azimuthal wave number (m number) is estimated to be ∼−50 from ground observations, while the theory of drift resonance gives m ∼− 49 for odd mode waves and ∼110‐keV protons, providing evidence that the drift resonance indeed took place in this event. We also found a steep earthward gradient of proton phase space density, which can quantitatively explain the wave excitation. The observed waves show typical features of giant pulsations (Pgs), regarding local time, m number, and flux oscillations. This study, therefore, has great implications to the field line mode structure and excitation mechanism of Pgs.