Effective Polytropic Indices of Anisotropic Planetary Magnetosheath Plasmas with Magnetoacoustic Waves

Meister, C.‐V.; Mäurer, Christoph; Hoffmann, D. H. H.

doi:10.1002/ctpp.201000071

Cited by 6 publications

(11 citation statements)

References 27 publications

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“…For example, the turbulent fluctuations can provide additional internal degrees of freedom and change the polytropic index [ Roussev et al ., ]. Slow magnetoacoustic waves, on the other hand, can change the polytropic index to be smaller than unity, which suggests that a compression of the plasma is accompanied by cooling [ Meister et al ., ].…”

Section: Discussionmentioning

confidence: 99%

“…A theoretical study of Meister et al . [] shows that the value of the polytropic index is not universal constant but depends on wave modes and the plasma population in turbulent systems. Their results show that slow magnetoacoustic waves have an effective polytropic index smaller than unity near the bow shock and in some proper magnetosheath and have an effective polytropic index larger than 2 in the vicinity of the magnetopause.…”

Section: Introductionmentioning

confidence: 99%

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Polytropic index of magnetosheath ions based on homogeneous MHD Bernoulli Integral

Pang

Cao

2016

JGR Space Physics

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This paper uses Cluster data during the period from 2001 to 2010 to study the polytropic processes of magnetosheath ions. Utilizing the method of homogeneous magnetohydrodynamic (MHD) Bernoulli integral (MBI), we first identify streamflow tubes, then use the constant of polytropic relation to guarantee that the streamflow tube experiences an unchanged polytropic process, and finally determine the polytropic index of ions in these streamflow tubes. The statistical results show that the magnetosheath is a complicated system in which the polytropic index of ions ranges from −2 to 3. The polytropic index distribution of ions is dependent on the electromagnetic energy flux perpendicular to the streamline. The median polytropic index of ions in the magnetosheath is 0.960, 0.965, and 0.974 for perpendicular electromagnetic energy ratio δE × B < 5%, δE × B < 3%, and δE × B < 1%, respectively. There are two basic polytropic processes in the magnetosheath: the dominant isothermal process and the isobaric process. When there is no exchange of electromagnetic energy between neighboring streamflow tubes, the magnetosheath ions are isothermal. However, when the perpendicular electromagnetic energy ratio increases, the isobaric polytropic process starts to emerge. The magnetosheath ion flows are highly localized because most streamflow tubes experiencing same polytropic processes last less than 60 s. Thus, the polytropic index of magnetosheath ion flows is highly variable.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polytropic index of magnetosheath ions based on homogeneous MHD Bernoulli Integral

Pang

Cao

2016

JGR Space Physics

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“…Song & Thomsen (1992) studied three magnetosheath passes with a slow mode transition in front of the magnetopause, and found that two of them have the same polytropic indices with α = 1.0 ± 0.1, and the other one has a similar polytropic index with α = 1.2 ± 0.1, i.e., the observed ions are closer to isothermal than to adiabatic. The theoretical results of Meister et al (2011) showed that the effective polytropic index of an anisotropic magnetosheath plasma depends on the wave modes.…”

Section: Introductionmentioning

confidence: 99%

Spatial Distribution and Low-frequency Disturbance Modulation of Magnetosheath Ion Polytropic Index

Pang

Geng

Wang

et al. 2022

ApJ

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We, using the Cluster data from 2001 to 2010, studied spatial distribution of the ion polytropic index in the magnetosheath, and the modulation of polytropic process by the low-frequency disturbances (4–18 mHz). The total of 30,3283 samples is divided into two sorts: quasi-perpendicular and quasi-parallel propagating ones. The median polytropic index increases with spreads narrowing from the bow shock to the magnetopause. The median polytropic indices are basically between isothermal and adiabatic in the inner magnetosheath, and between isothermal and isobaric in the outer magnetosheath. The spatial distributions of the correlation coefficient (CC) between the perturbed ion number density and the parallel magnetic field CC (δn, δB ∥) have a good correlation with those of polytropic index. The quasi-perpendicular disturbances are mostly mirror-like modes (D r ≪ 1) except for some slow-mode disturbances (D r ≥ 1) in the regions near the Sun–Earth line and the inner magnetosheath. The polytropic indices in the inner and middle magnetosheath modulated by mirror-like-mode disturbances are between 0.9 and 1.3. The quasi-parallel propagating low-frequency disturbances are predominantly slow modes in the inner and middle magnetosheath, and Alfvén modes in the outer magnetosheath. For the samples with quasi-parallel propagating disturbances, the polytropic processes are basically between isothermal and isobaric except near the magnetopause. The good correlation between the spatial distributions of polytropic index and low-frequency disturbances indicates that the distribution of the polytropic index in the magnetosheath is modulated by low-frequency disturbances.

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“…Using the double‐polytropic closure for the anisotropic magnetosheath plasma, Hau et al () showed that the magnetosheath plasma typically behaves more like quasi‐isothermal conditions (α ⊥ = 0.94 ± 0.10 and α ∥ = 1.14 ± 0.13), rather than adiabatic conditions (α ⊥ = 2 and α ∥ = 3). Pudovkin et al () and Meister et al () examined the thermodynamic properties for magnetized anisotropic plasma using the anisotropic magnetohydrodynamics (MHD) with the double‐adiabatic law and suggested that the effective polytropic index, which is characterized by the relationship between the total thermal energy and the number density of the plasma in their studies, depends both on the characteristics of the plasma flow and on the temperature anisotropy. Using the polytropic relation and Bernoulli's theorem, Pang et al () examined the polytropic indices for magnetosheath ions estimated along the same streamline and found that their probability distribution has a major peak near 1 (that is, quasi‐isothermal process) with a minor peak near 0 (that is, quasi‐isobaric process).…”

Section: Introductionmentioning

confidence: 99%

Dependence of Thermodynamic Processes on Upstream Interplanetary Magnetic Field Conditions for Magnetosheath Ions

et al. 2019

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Using Time History of Events and Macroscale Interactions during Substorms (THEMIS)observations over a 10-year period from 2008 to 2017, we statistically investigate the thermodynamic properties for magnetosheath ions and their dependence on upstream interplanetary magnetic field (IMF) conditions. The thermodynamic properties for magnetosheath ions are estimated by using the polytropic index averaged over the subinterval that belongs to the same streamline (α). The THEMIS observations show that the probability distribution of α for magnetosheath ions has a major peak at α~1 (quasi-isothermal conditions) with a longer left tail down to α~0 (quasi-isobaric conditions). The spatial distributions of α for two different types according to IMF spiral angle (i.e., Parker spiral and ortho-Parker spiral IMF orientations) reveal that the ions in the downstream of a quasi-perpendicular shock (quasi-perpendicular magnetosheath) exhibit quasi-isothermal processes, while those in the downstream of a quasi-parallel shock (quasi-parallel magnetosheath) show α lower than unity (down to α 0.8) implying the anticorrelation between the ion temperature and the ion number density variations. Moreover, α in the quasi-parallel magnetosheath tends to decrease with increasing magnetic local time distance from the magnetic local noon. These results indicate that the thermodynamic properties for magnetosheath ions depend on the bow shock geometry (quasi-perpendicular bow shocks versus quasi-parallel bow shocks) and are presumably controlled by a variety of instabilities, waves, and turbulence in the magnetosheath. Key Points:• The probability distribution of the polytropic index for magnetosheath ions has a major peak at 1 with a longer left tail down to 0 • Ions in the quasi-perpendicular magnetosheath exhibit quasi-isothermal processes • In the quasi-parallel magnetosheath, the variations in the ion temperature are anticorrelated with those in the ion number density Supporting Information:• Supporting Information S1• Figure S1 • Figure S2

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Effective Polytropic Indices of Anisotropic Planetary Magnetosheath Plasmas with Magnetoacoustic Waves

Cited by 6 publications

References 27 publications

Polytropic index of magnetosheath ions based on homogeneous MHD Bernoulli Integral

Polytropic index of magnetosheath ions based on homogeneous MHD Bernoulli Integral

Spatial Distribution and Low-frequency Disturbance Modulation of Magnetosheath Ion Polytropic Index

Dependence of Thermodynamic Processes on Upstream Interplanetary Magnetic Field Conditions for Magnetosheath Ions

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