arXiv 2009.040892020-09-09physics.space-ph

磁螺旋度特征及其在调节太阳风中磁能谱和质子温度中的作用

Magnetic helicity signature and its role in regulating magnetic energy spectra and proton temperatures in the solar wind

G. Q. Zhao, Y. Lin, X. Y. Wang, H. Q. Feng, D. J. Wu, H. B. Li, A. Zhao, Q. Liu

备注：: 28 pages, 8 figures
DOI：: 10.3847/1538-4357/abca3b

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摘要：

在以前的论文中，我们发现质子温度与太阳风中的质子尺度湍流有明显的联系，磁螺旋度信号似乎是这种联系的一个重要指标。本文根据15年的现场观测，进一步研究了太阳风湍流的磁螺旋度及其对磁能谱和质子温度的调节作用。结果表明，在$0.3 \lesssim kρ_p \lesssim 1$尺度下，螺旋度特征在太阳风湍流中非常普遍，其中$k$是波数，$ρ_p$是质子回旋半径。螺旋度的符号大多为正，表明湍流的右旋偏振占主导地位。当$kρ_p$和$β_{{\parallel}p}$小于1时，螺旋度大小通常随$k$和$β_{{\parallel}p}$（质子平行β）增加。随着螺旋度的增加，能谱的功率指数变得更负，质子温度$T_{{\perp}p}$和$T_{{\parallel}p}$显著上升，其中$T_{{\perp}p}$和$T_{{\parallel}p}$是相对于背景磁场的垂直和平行温度。特别地，当满足$β_{{\parallel}p} < 1$时，$T_{{\perp}p}$的上升比$T_{{\parallel}p}$快。$T_{{\perp}p}$随螺旋度幅值的快速上升可以解释为动力阿尔文波（KAW）湍流优先垂直加热太阳风质子的结果。

英文摘要：

In a previous paper, we found that proton temperatures are clearly associated with the proton-scale turbulence in the solar wind, and magnetic helicity signature appears to be an important indicator in the association. Based on 15 years of in situ measurements, the present paper further investigates the magnetic helicity of solar wind turbulence and its role in regulating magnetic energy spectra and proton temperatures. Results show that the presence of the helicity signature is very common in solar wind turbulence at scales $0.3 \lesssim kρ_p \lesssim 1$, with $k$ being the wavenumber and $ρ_p$ the proton gyroradius. The sign of the helicity is mostly positive, indicating the dominance of right-handed polarization of the turbulence. The helicity magnitude usually increases with $k$ and $β_{{\parallel}p}$ (the proton parallel beta) when $kρ_p$ and $β_{{\parallel}p}$ are less than unity. As helicity magnitude increases, the power index of the energy spectrum becomes more negative, and the proton temperatures $T_{{\perp}p}$ and $T_{{\parallel}p}$ rise significantly, where $T_{{\perp}p}$ and $T_{{\parallel}p}$ are the perpendicular and parallel temperatures with respect to the background magnetic field. In particular, the rise of $T_{{\perp}p}$ is faster than $T_{{\parallel}p}$ when $β_{{\parallel}p} < 1$ is satisfied. The faster rise of $T_{{\perp}p}$ with the helicity magnitude may be interpreted as the result of the preferentially perpendicular heating of solar wind protons by kinetic Alfvén wave (KAW) turbulence.

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