EVIDENCE OF THE ION CYCLOTRON RESONANCE AT PROTON KINETIC SCALES IN THE SOLAR WIND
EVIDENCE OF THE ION CYCLOTRON RESONANCE AT PROTON KINETIC SCALES IN THE SOLAR WIND
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DOI：
10.1088/0004-637x/802/1/1
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
O. Roberts;Xing Li
中科院分区：
文献类型：
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作者：
O. Roberts;Xing Li
k滤波和波极化技术被应用于四个快速自由（与地球前震无关）太阳风区间的星团磁场数据。除了通常观测到的以与全局平均场\(B_0\)准垂直角度传播的磁场波动群外，在无法确定局部等离子体不稳定性时，也观测到了以准平行角度传播的波动群。在低波数（\(kv_A /\Omega_p \leqslant 0.6\)）时，两种成分都存在，且具有相似强度的功率，而在高波数（\(kv_A\Omega_p > 0.6\)）时，只能识别出垂直成分。这里\(v_A\)和\(\Omega_p\)分别是阿尔文速度和质子（角）回旋频率，\(k\)表示波数。所得到的色散曲线（以及左旋和右旋极化波动幅度的比值）在\((kv_A /\Omega_p) \sim 0.6\)处显示出急剧的转变（和下降），这对应于航天器频率\(f_{sc} = 0.32\)Hz。在更高的波数下，测量结果与先前的研究一致，表明存在动力学阿尔文波（KAW）湍流或KAW湍流与对流结构的混合。平行成分呈现出一种标度，其中谱指数\(\delta\)在约\(5/3\)和\(2\)之间变化，尽管数据点的数量不足以保证精确确定。观测到的平行成分的起源尚不清楚。平行成分的存在与离子回旋波是一致的，并且我们将该成分在高波数下的急剧下降解释为在所研究的太阳风区间中发生离子回旋共振的证据。
The k-filtering and wave polarization techniques are applied to Cluster magnetic field data at four intervals of fast free (not connected to Earth's foreshock) solar wind. In addition to the commonly observed population of magnetic field fluctuations propagating at quasi-perpendicular angles to the global mean field B0, a population of fluctuations propagating at quasi-parallel angles are also observed when no local plasma instability can be identified. At low wavenumbers (kvA/Ωp ⩽ 0.6) both components are present, and have powers of similar strength, while at higher wavenumbers (kvAΩp > 0.6) only the perpendicular component can be identified. Here vA and Ωp are the Alfvén speed and the proton (angular) gyration frequency, k denotes the wavenumber. The dispersion curve obtained (and the ratio of the magnitudes of left and right hand polarized fluctuations) shows a sharp transition (and decrease) at (kvA/Ωp) ∼ 0.6, which corresponds to a spacecraft frequency fsc = 0.32 Hz. At higher wavenumbers the measurements agree with previous studies indicating the presence of kinetic Alfvén wave (KAW) turbulence or a mixture of KAW turbulence and convected structures. The parallel component displays a scaling of where the spectral index δ ranges between about 5/3 and 2 although the number of data points does not warrant an accurate determination. The origins of the observed parallel component are unclear. The presence of a parallel component is consistent with ion cyclotron waves, and we interpret the sharp drop of this component at higher wavenumbers as evidence that the ion cyclotron resonance is occurring in the solar wind intervals studied.