The Role of Proton Cyclotron Resonance as a Dissipation Mechanism in Solar Wind Turbulence: A Statistical Study at Ion-kinetic Scales
The Role of Proton Cyclotron Resonance as a Dissipation Mechanism in Solar Wind Turbulence: A Statistical Study at Ion-kinetic Scales
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DOI：
10.3847/1538-4357/aab03d
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发表时间：
2018-01
期刊：
影响因子：
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通讯作者：
Lloyd D. Woodham;R. Wicks;D. Verscharen;C. Owen
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文献类型：
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作者：
Lloyd D. Woodham;R. Wicks;D. Verscharen;C. Owen
我们使用磁场和离子矩数据从MFI和SWE仪器上的风航天器研究太阳风湍流的性质在离子动力学尺度。我们使用自动化程序分析了2012年期间0.1和5.4 Hz之间磁场波动的光谱特性，计算高分辨率92 s功率和磁螺旋度谱。为了确保光谱特征是物理的，我们在2004年初使用地球磁层的尾瓣交叉点对MFI“噪声本底”进行了首次飞行测量。我们利用泰勒的假设多普勒频移到航天器的频率框架，发现在这些频率下观察到的频谱中断与质子回旋共振标度1/kc最相关，而不是质子惯性长度di或质子回旋标度ρi。当我们考虑周期时，这种一致性是最强的，其中，和与di处的谱突变和ρi处的谱突变相一致。我们还发现，在这些频率下观测到的相干磁螺旋度特征在低频下以1/kc为界，其绝对值在ρi处达到最大值。这些结果适用于慢速和快速的气流，但在螺旋度特征最强的Alfvénic快速风中具有更好的相关性。我们的结论是，这些研究结果是一致的质子回旋共振作为一个重要的机制，在太阳风中的湍流能量耗散，发生在我们选定的间隔至少有一半的时间。但是，我们不排除其他机制。
We use magnetic field and ion moment data from the MFI and SWE instruments on board the Wind spacecraft to study the nature of solar wind turbulence at ion-kinetic scales. We analyze the spectral properties of magnetic field fluctuations between 0.1 and 5.4 Hz during 2012 using an automated routine, computing high-resolution 92 s power and magnetic helicity spectra. To ensure the spectral features are physical, we make the first in-flight measurement of the MFI “noise-floor” using tail-lobe crossings of the Earth’s magnetosphere during early 2004. We utilize Taylor’s hypothesis to Doppler-shift into the spacecraft frequency frame, finding that the spectral break observed at these frequencies is best associated with the proton cyclotron resonance scale, 1/kc, rather than the proton inertial length, di, or proton gyroscale, ρi. This agreement is strongest when we consider periods where , and is consistent with a spectral break at di for and at ρi for . We also find that the coherent magnetic helicity signature observed at these frequencies is bounded at low frequencies by 1/kc, and its absolute value reaches a maximum at ρi. These results hold in both slow and fast wind streams, but with a better correlation in the more Alfvénic fast wind where the helicity signature is strongest. We conclude that these findings are consistent with proton cyclotron resonance as an important mechanism for dissipation of turbulent energy in the solar wind, occurring at least half the time in our selected interval. However, we do not rule out additional mechanisms.