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arXiv 2307.09800astro-ph.SRphysics.plasm-phphysics.space-ph
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内日球层行星际日冕物质抛射的湍流特性:对质子β和磁通量绳结构的依赖性

Turbulence Properties of Interplanetary Coronal Mass Ejections in the Inner Heliosphere: Dependence on Proton Beta and Flux Rope Structure

S. W. Good, O. K. Rantala, A. -S. M. Jylhä, C. H. K. Chen, C. Möstl, E. K. J. Kilpua

AI总结:

本研究分析内日球层ICMEs的磁场涨落功率谱,发现大尺度谱特性由通量绳结构主导,过渡-动力学特性受低质子β影响,而惯性范围谱指数保持约-5/3,表明湍流标度具有系统无关性。

摘要:

行星际日冕物质抛射(ICMEs)在广泛日心距离范围内具有低质子β和大尺度磁通量绳结构,使其成为研究太阳风涨落的独特环境。本文研究了由Solar Orbiter和Parker Solar Probe在0.25至0.95天文单位(au)之间观测到的28个ICMEs中磁场涨落的功率谱。在大尺度上,谱由通量绳内包含的功率主导。扣除背景通量绳场后,在$kd_i \leq 10^{-3}$范围内,平均谱指数从$-5/3$降至$-3/2$。通量绳扣除还揭示了磁场中更短的相关长度。在所有径向距离处,无论是否扣除通量绳,惯性范围内的谱指数通常接近$-5/3$,并在向动力学尺度过渡时陡化至一致低于$-3$的值。终止惯性范围的高频断裂点随径向距离近似线性演化,其尺度更接近质子惯性长度而非质子回旋尺度,这与低质子β等离子体的预期一致。惯性尺度上的磁压缩性未显示出与径向距离的任何显著相关性,这与一般太阳风情况形成对比。在ICMEs中,注入尺度上的独特谱特性主要取决于全局通量绳结构,而过渡-动力学特性则更多受低质子β影响;介于两者之间的惯性范围似乎与ICME的这两个特征均无关,表明湍流具有与系统无关的标度性。

英文摘要:

Interplanetary coronal mass ejections (ICMEs) have low proton beta across a broad range of heliocentric distances and a magnetic flux rope structure at large scales, making them a unique environment for studying solar wind fluctuations. Power spectra of magnetic field fluctuations in 28 ICMEs observed between 0.25 and 0.95 au by Solar Orbiter and Parker Solar Probe have been examined. At large scales, the spectra were dominated by power contained in the flux ropes. Subtraction of the background flux rope fields reduced the mean spectral index from $-5/3$ to $-3/2$ at $kd_i \leq 10^{-3}$. Rope subtraction also revealed shorter correlation lengths in the magnetic field. The spectral index was typically near $-5/3$ in the inertial range at all radial distances regardless of rope subtraction, and steepened to values consistently below $-3$ with transition to kinetic scales. The high-frequency break point terminating the inertial range evolved approximately linearly with radial distance and was closer in scale to the proton inertial length than the proton gyroscale, as expected for plasma at low proton beta. Magnetic compressibility at inertial scales did not show any significant correlation with radial distance, in contrast to the solar wind generally. In ICMEs, the distinctive spectral properties at injection scales appear mostly determined by the global flux rope structure while transition-kinetic properties are more influenced by the low proton beta; the intervening inertial range appears independent of both ICME features, indicative of a system-independent scaling of the turbulence.

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