Propagation of Electromagnetic Ion Cyclotron Waves in a Dipole Magnetic Field: A 2‐D Hybrid Simulation
Propagation of Electromagnetic Ion Cyclotron Waves in a Dipole Magnetic Field: A 2‐D Hybrid Simulation
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DOI：
10.1029/2021ja029720
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发表时间：
2021-12
期刊：
影响因子：
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通讯作者：
N. Kang;Q. Lu;Xinliang Gao;Xueyi Wang;Huayue Chen;Shui Wang
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文献类型：
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作者：
N. Kang;Q. Lu;Xinliang Gao;Xueyi Wang;Huayue Chen;Shui Wang
电磁离子回旋波(EMIC)是地球磁层内常见的等离子体波之一，在辐射带和环电流的粒子动力学中起着至关重要的作用。磁化波是由质子温度各向异性激发的，通常具有左手极化，然而，卫星观测通常报告在内磁层中存在线性极化的电磁波。本文采用偶极场中的二维混合程序(gcPIC-HIXED)模拟了赤道源区电磁波的传播。我们跟踪单个EMIC波包，并分析其特性是如何沿着其轨迹演化的。在对包的波法向角(WNA)进行诊断时，我们提出了一种新的波前形状识别(WFSI)方法。知道WNA后，椭圆度也可以计算出来。通过比较由线性理论计算的椭圆度和由模拟得到的椭圆度，我们得出结论：在质子-电子等离子体中，EMIC波在向更高纬度传播并倾斜时，由于传播效应，将从左手极化转变为线极化。我们还发现，波包的峰值频率(波幅最大的波模)在向高纬度传播时降低，这是由于不同模式的增长和衰减行为不同所致。
Electromagnetic ion cyclotron (EMIC) waves are one commonly observed plasma waves in the Earth's inner magnetosphere and play a crucial role in particle dynamics in the radiation belt and ring current. EMIC waves are excited by a proton temperature anisotropy and generally have a left‐handed polarization, however satellite observations have usually reported the existence of linearly polarized EMIC waves in the inner magnetosphere. In this paper, we employ a two‐dimensional (2D) hybrid code in a dipole field (gcPIC‐hybrid) to simulate the propagation of EMIC waves from the equatorial source region. We track one single EMIC wave packet and analyze how its properties evolve along its trajectory. In diagnosing the wave normal angle (WNA) of the packet, we propose a novel method called Wave Front Shape Identification (WFSI). The ellipticity can also been calculated after we know the WNA. By comparing the ellipticity calculated from the linear theory and the ellipticity diagnosed from the simulation, we conclude that in a proton‐electron plasma, EMIC waves would turn from a left‐handed polarization to a linear polarization solely due to the propagation effect when the waves propagate toward higher latitudes and become oblique. We also find that the peak frequency of the wave packet (the wave mode with the maximum amplitude) decreases when propagating toward higher latitudes, which is due to different growth and damping behavior of different modes.