阿雷西博多频IPS观测:太阳风密度湍流尺度及其各向异性

IF 2.7 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS
P. K. Manoharan, C. J. Salter
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引用次数: 0

摘要

本文分析了用阿雷西博305米射电望远镜在第24太阳周期结束和第25太阳周期开始的最小阶段进行的行星际闪烁(IPS)观测。这些观测跨越了~ 300到3100 MHz的宽频率范围,包括P、L和s波段,覆盖了~ 5到200太阳半径的日心距离。每个l波段观测提供了大约600兆赫带宽上的同时测量。此外,只要可行,在所有三个频带上对光源进行近乎同时的测量,对于研究沿同一视线穿过日球层的更宽频带上的闪烁特性是有用的。在l波段获得的闪烁动态谱显示,闪烁指数从最低频率到最高频率有系统地降低,这为了解太阳风密度对闪烁的影响提供了有价值的见解。对L波段多个源的闪烁指数(\(m\))的分析,以及对覆盖P、L和s波段的选定源的近同时观测,清楚地表明波长依赖\(m \propto \lambda ^{\omega }\),当考虑到散射屏的有效距离\(z\)时,这必然导致\(m\)对菲涅耳尺度的依赖。指数\(\omega \)在∼1 ~ 1.8之间。根据多日观测(即在一系列太阳抵消以减轻太阳风湍流可能的逐日变化的影响)确定的一个源的平均\(\omega \)值在各个源之间表现出变变性。关于闪烁的径向依赖性的结果与先前的IPS测量结果一致。在宽频率范围内获得的时间功率谱表现出与波长相关的功率级演化,并随着观测频率的增加而展宽。此外,随着观测频率的增加,频谱中“菲涅耳膝”的时间频率舍入增加表明了一种新的现象:随着密度-湍流结构尺度的减小,各向异性增加。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Arecibo Multifrequency IPS Observations: Solar-Wind Density Turbulence Scale Sizes and Their Anisotropy

We present an analysis of interplanetary scintillation (IPS) observations conducted with the Arecibo 305-m radio telescope during the minimum phase at the end of Solar Cycle 24 and the onset of Solar Cycle 25. These observations span a broad frequency range of ∼ 300 to 3100 MHz, encompassing the P-, L-, and S-bands, and cover heliocentric distances from ∼ 5 to 200 solar radii. Each L-band observation provided simultaneous measurements across a bandwidth of approximately 600 MHz. Furthermore, whenever feasible, the near-simultaneous measurements of a source acquired across all three frequency bands were useful to study the scintillation characteristics over a much wider frequency band along the same line of sight through the heliosphere. The dynamic spectrum of the scintillations obtained at the L-band shows a systematic decrease in the scintillation index from the lowest to the highest frequency, offering valuable insight into the influence of the solar wind density microstructures responsible for scintillation. Analyses of the scintillation index (\(m\)) for multiple sources at the L-band, along with near-simultaneous observations of selected sources covering the P-, L-, and S-bands, clearly demonstrate a wavelength dependence of \(m \propto \lambda ^{\omega }\), which inherently leads to a dependence of \(m\) on the Fresnel scale, when considering the effective distance to the scattering screen, \(z\). The index \(\omega \) ranges between ∼ 1 and 1.8. The average \(\omega \) value of a source, determined from observations made on multiple days (i.e., at a range of solar offsets to mitigate the influence of possible day-to-day variations in solar-wind turbulence) exhibits variability across sources. The results on the radial dependence of scintillation agree with earlier IPS measurements. The temporal power spectra obtained over the wide frequency range exhibit a power-level evolution in accordance with the wavelength dependence and a broadening with an increasing observation frequency. Furthermore, the increased temporal–frequency rounding of the “Fresnel knee” in the spectrum with the observing frequency suggests a novel phenomenon: an increase in anisotropy as the scale size of the density–turbulence structure decreases.

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来源期刊
Solar Physics
Solar Physics 地学天文-天文与天体物理
CiteScore
5.10
自引率
17.90%
发文量
146
审稿时长
1 months
期刊介绍: Solar Physics was founded in 1967 and is the principal journal for the publication of the results of fundamental research on the Sun. The journal treats all aspects of solar physics, ranging from the internal structure of the Sun and its evolution to the outer corona and solar wind in interplanetary space. Papers on solar-terrestrial physics and on stellar research are also published when their results have a direct bearing on our understanding of the Sun.
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