Long-Term Variability of the Polytropic Index of Solar Wind Protons at 1 AU

Nicolaou, Georgios; Livadiotis, G.; Moussas, X.

doi:10.1007/s11207-013-0401-x

Cited by 58 publications

(71 citation statements)

References 11 publications

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“…It is generally accepted that when electromagnetic energy flux perpendicular to flow velocity

\overset{⇀}{v}

is much smaller than other terms, the MHD Bernoulli integral can still be considered to be quasi‐invariant along streamline. For example, for the solar wind, since the electromagnetic term is much smaller than the kinetic energy term, the electromagnetic term can be ignored no matter Poynting vector

\overset{⇀}{E} \times \overset{⇀}{B}

is or not parallel to flow velocity

\overset{⇀}{v}

[ Kartalev et al ., ; Nicolaou et al ., ]. However, for the magnetotail plasma sheet, the situation is slightly different.…”

Section: Description Of the Approachmentioning

confidence: 99%

“…Finally, we analyzed the distribution of polytropic indexes in different AE levels ( AE ≥ 200 nT and AE < 200 nT, respectively) by statistics for all streamflow tubes obtained from the data of Cluster in 2001–2009. This method has been used in estimating the polytropic index of solar wind [ Kartalev et al ., ; Nicolaou et al ., ]. It should be noted that in this paper we studied only the polytropic index α , which is different from the ratio of specific heats γ .…”

Section: Introductionmentioning

confidence: 99%

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Polytropic index of central plasma sheet ions based on MHD Bernoulli integral

et al. 2015

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This paper uses the data of Cluster from 2001 to 2009 to study the polytropic processes of central plasma sheet (CPS) ions. We first adopt the approach of MHD Bernoulli integral (MBI) to identify homogeneous streamflow tubes (quasi-invariant MBI regions) and then calculate the polytropic index of ions for those streamflow tubes whose outward electromagnetic energy ratios δ < 0.05. The central plasma sheet is actually a complicated system, which comprises many streamflow tubes with different polytropic relations and the transition layers in between. The polytropic indexes of the CPS ions range from 0.1 to 1.8 and have a quasi-Gaussian distribution. The median polytropic index is 0.93 for AE < 200 nT and 0.91 for AE ≥ 200 nT. Thus, there is no obvious difference between the polytropic indexes of the quiet time and the substorm time CPS ions, which suggests that the thinning and thickening processes of plasma sheet during substorm times do not change obviously the polytropic relation of the CPS ions. The statistical analysis using different δ (δ < 0.05, 0.025, and 0.01) shows that the outward emission of electromagnetic energy is an effective cooling mechanism and can make the polytropic index to decrease and shift toward isobaric. It is inferred that the CPS ions as a whole much likely behave in a way between isobaric and isothermal.

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“…It is generally accepted that when electromagnetic energy flux perpendicular to flow velocity

\overset{⇀}{v}

\overset{⇀}{E} \times \overset{⇀}{B}

is or not parallel to flow velocity

\overset{⇀}{v}

[ Kartalev et al ., ; Nicolaou et al ., ]. However, for the magnetotail plasma sheet, the situation is slightly different.…”

Section: Description Of the Approachmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polytropic index of central plasma sheet ions based on MHD Bernoulli integral

et al. 2015

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“…Zhu (1990) statistically analyzed the data of plasma number density and pressure measured by ISEE satellite from and found that the polytropic index in the CPS is 1.08 for AE < 100 nT and 1.31 for AE > 100 nT, respectively. The approach of MHD Bernoulli Integral is considered to be one of the best methods to calculate polytropic index since it can guarantee that the used data come approximately from the same unit (Kartalev et al, 2006;Nicolaou et al, 2014;Pang et al, 2016). The approach of MHD Bernoulli Integral is considered to be one of the best methods to calculate polytropic index since it can guarantee that the used data come approximately from the same unit (Kartalev et al, 2006;Nicolaou et al, 2014;Pang et al, 2016).…”

Section: 1029/2019ja026681mentioning

confidence: 99%

Kinetic Analysis of the Energy Transport of Two‐Flow Components in the Plasma Sheet

Cao

Ren

2019

JGR Space Physics

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Satellite observations indicate that multiple components often exist in the plasma sheet, particularly during impulsive fast flow events. In this paper, we perform a kinetic analysis of the energy transport of plasma sheet ion flow using a model of two‐component plasma sheet ion flows (Background convection flow represented by subscript “b” and Fast flow represented by subscript “f”) and compare the energy transport calculated by kinetic approach Qk with those obtained from magnetohydrodynamic (MHD) approach QMHD. The ratio of Qk/QMHD is always larger than unity and is positively proportional to the ratios of Vf/Vb and Tf/Tb. The maximum values of Qk/QMHD occur in the low‐speed ranges (i.e., small density ratio Nf/N). When Nf/N exceeds 0.4, the ratio of Qk/QMHD is almost the same for a wide parameter ranges of Vf, Tf, and Vb. Heat flux is important in low‐speed range and is neglectable in the high‐speed range. The adiabatic polytropic index 5/3 cannot correctly describe energy transport rate. A density ratio Nf/N of 0.3% of high‐speed ion flow can make the effective polytropic index obviously deviate from adiabatic polytropic index (5/3). The above theoretic results can well explain previously reported satellite in situ observations.

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“…For example, while the upstream solar wind has atypical polytropic index around the adiabatic value ofγ∼5/3 (e.g., Nicolaou et al 2014;Livadiotis & Desai 2016), for the downstream plasma in the inner heliosheath, there is nosuch evidence; on the contrary, there are cases where the measured γ is quite different, i.e., near the isobaric value, γ∼0 (e.g., Livadiotis & McComas 2012. Following previous studies, we consider the same upstream and downstream polytropic index for the shock transition.…”

Section: Subsonic Plasma Flow In the Heliosheathmentioning

confidence: 99%

Modeling the Plasma Flow in the Inner Heliosheath with a Spatially Varying Compression Ratio

Nicolaou

Livadiotis

2017

ApJ

Self Cite

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We examine asemi-analytical non-magnetic model of the termination shock locationpreviously developed by Exarhos & Moussas. In their study, the plasma flow beyond the shock is considered incompressible and irrotational, thus the flow potential is analytically derived from the Laplace equation. Here we examine the characteristics of the downstream flow in the heliosheath in order to resolve several inconsistencies existing in theExarhos & Moussas model. In particular, the model is modified in order to be consistent with the RankineHugoniot jump conditions and the geometry of the termination shock. It is shown that a shock compression ratio varying along the latitude can lead to physically correct results. We describe the new model and present several simplified examples for a nearly spherical, strong termination shock. Under those simplifications, the upstream plasma is nearly adiabatic for large (∼100 AU) heliosheath thickness.

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Long-Term Variability of the Polytropic Index of Solar Wind Protons at 1 AU

Cited by 58 publications

References 11 publications

Polytropic index of central plasma sheet ions based on MHD Bernoulli integral

Polytropic index of central plasma sheet ions based on MHD Bernoulli integral

Kinetic Analysis of the Energy Transport of Two‐Flow Components in the Plasma Sheet

Modeling the Plasma Flow in the Inner Heliosheath with a Spatially Varying Compression Ratio

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