Dependence of the polytropic behaviour of solar wind protons on temperature anisotropy and plasma β near L1

IF 5.4 2区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS
C. Katsavrias, G. Nicolaou, G. Livadiotis
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引用次数: 0

Abstract

Context. A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature, while the value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom of that specific process.Aims. In this paper we investigate in depth the relationship between the proton effective polytropic index γ in the solar wind, the proton anisotropy α, and plasma β, while – for the first time to our knowledge to such an extent – we further investigate the dependence of the partial (with respect to the magnetic field) polytropic index to both the above-mentioned plasma parameters.Methods. To this end we use the entire Wind dataset spanning the 1995 to 2023 time period to derive the distributions of the polytropic index in the near-Earth space (L1).Results. Our results indicate that the proton γ increases with increasing proton anisotropy and decreases with increasing plasma β. Finally, we show that even though the average (over long time periods) total and partial proton polytropic index values are very close, these values correspond to isotropic plasma alone, with a further balance between the thermal and magnetic pressure.On the contrary, for shorter time periods and/or specific solar wind structures, where the proton anisotropy and plasma β exhibit deviations from these average values, the partial proton polytropic index exhibits significant variation that is dependent on the anisotropy and on plasma β.
太阳风质子的多向性行为与 L1 附近温度各向异性和等离子体 β 的关系
背景。多向过程通过流体密度和温度之间的特定关系描述了流体从一种状态向另一种状态的转变,而支配这种关系的多向指数值决定了该特定过程的传热和有效自由度。在本文中,我们深入研究了太阳风中质子有效多向性指数γ、质子各向异性α和等离子体β之间的关系,同时--据我们所知第一次在如此大的程度上--我们进一步研究了部分(相对于磁场)多向性指数对上述两个等离子体参数的依赖性。为此,我们使用了 1995 年至 2023 年的整个 Wind 数据集,得出了近地空间(L1)的多向性指数分布。我们的结果表明,质子γ随质子各向异性的增加而增加,随等离子体β的增加而减小。最后,我们表明,尽管质子多向性指数的平均值(在较长的时间段内)总值和部分值非常接近,但这些值只对应于各向同性的等离子体,热压和磁压进一步平衡。相反,在较短的时间段和/或特定的太阳风结构中,质子各向异性和等离子体β偏离了这些平均值,部分质子多向性指数表现出显著的变化,这种变化取决于各向异性和等离子体β。
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来源期刊
Astronomy & Astrophysics
Astronomy & Astrophysics 地学天文-天文与天体物理
CiteScore
10.20
自引率
27.70%
发文量
2105
审稿时长
1-2 weeks
期刊介绍: Astronomy & Astrophysics is an international Journal that publishes papers on all aspects of astronomy and astrophysics (theoretical, observational, and instrumental) independently of the techniques used to obtain the results.
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