scholarly journals Relationship between Polytropic Index and Temperature Anisotropy in Space Plasmas

2021 ◽  
Vol 909 (2) ◽  
pp. 127
Author(s):  
G. Livadiotis ◽  
G. Nicolaou
Keyword(s):  
Space Plasmas ◽  
Polytropic Index ◽  
Temperature Anisotropy

scholarly journals Temperature anisotropy instabilities stimulated by the interplay of the core and halo electrons in space plasmas

2018 ◽  
Vol 25 (2) ◽  
pp. 022902 ◽  
Author(s):  
M. Lazar ◽  
S. M. Shaaban ◽  
H. Fichtner ◽  
S. Poedts
Keyword(s):  
Space Plasmas ◽  
Temperature Anisotropy ◽  
The Core

scholarly journals Whistler instabilities from the interplay of electron anisotropies in space plasmas: a quasi-linear approach

2019 ◽  
Vol 492 (3) ◽  
pp. 3529-3539 ◽  
Author(s):  
S M Shaaban ◽  
M Lazar
Keyword(s):  
Heat Flux ◽  
Free Energy ◽  
Cumulative Effects ◽  
Space Plasmas ◽  
Stable States ◽  
Temperature Anisotropy ◽  
Realistic Interpretation ◽  
Linear Approach ◽  
Statistical Studies ◽  
Equipartition Of Energy

ABSTRACT Recent statistical studies of observational data unveil relevant correlations between whistler fluctuations and the anisotropic electron populations present in space plasmas, e.g. solar wind and planetary magnetospheres. Locally, whistlers can be excited by two sources of free energy associated with anisotropic electrons, i.e. temperature anisotropies and beaming populations carrying the heat flux. However, these two sources of free energy and the resulting instabilities are usually studied independently preventing a realistic interpretation of their interplay. This paper presents the results of a parametric quasi-linear study of the whistler instability cumulatively driven by two counter-drifting electron populations and their anisotropic temperatures. By comparison to individual regimes dominated either by beaming population or by temperature anisotropy, in a transitory regime the instability becomes highly conditioned by the effects of both these two sources of free energy. Cumulative effects stimulate the instability and enhance the resulting fluctuations, which interact with electrons and stimulate their diffusion in velocity space, leading to a faster and deeper relaxation of the beaming velocity associated with a core heating in perpendicular direction and a thermalization of the beaming electrons. In particular, the relaxation of temperature anisotropy to quasi-stable states below the thresholds conditions predicted by linear theory may explain the observations showing the accumulation of these states near the isotropy and equipartition of energy.

scholarly journals Solar wind temperature anisotropy constraints from streaming instabilities

2018 ◽  
Vol 613 ◽  
pp. A23 ◽  
Author(s):  
S. Vafin ◽  
M. Lazar ◽  
H. Fichtner ◽  
R. Schlickeiser ◽  
M. Drillisch
Keyword(s):  
Solar Wind ◽  
Large Deviations ◽  
The Other ◽  
Space Plasmas ◽  
Plasma Stability ◽  
Particle Collisions ◽  
Temperature Anisotropy ◽  
Large Interval ◽  
Low Rate ◽  
Kinetic Instabilities

Due to the relatively low rate of particle-particle collisions in the solar wind, kinetic instabilities (e.g., the mirror and firehose) play an important role in regulating large deviations from temperature isotropy. These instabilities operate in the high β∥ > 1 plasmas, and cannot explain the other limits of the temperature anisotropy reported by observations in the low beta β∥ < 1 regimes. However, the instability conditions are drastically modified in the presence of streaming (or counterstreaming) components, which are ubiquitous in space plasmas. These effects have been analyzed for the solar wind conditions in a large interval of heliospheric distances, 0.3–2.5 AU. It was found that proton counter-streams are much more crucial for plasma stability than electron ones. Moreover, new instability thresholds can potentially explain all observed bounds on the temperature anisotropy, and also the level of differential streaming in the solar wind.

scholarly journals On the Calculation of the Effective Polytropic Index in Space Plasmas

Entropy ◽  
2019 ◽  
Vol 21 (10) ◽  
pp. 997 ◽  
Author(s):  
Georgios Nicolaou ◽  
George Livadiotis ◽  
Robert T. Wicks
Keyword(s):  
Plasma Density ◽  
Plasma Temperature ◽  
Statistical Error ◽  
Space Plasmas ◽  
Polytropic Index ◽  
Plasma Measurement ◽  
Wind Spacecraft ◽  
Index Value ◽  
The Relationship

The polytropic index of space plasmas is typically determined from the relationship between the measured plasma density and temperature. In this study, we quantify the errors in the determination of the polytropic index, due to uncertainty in the analyzed measurements. We model the plasma density and temperature measurements for a certain polytropic index, and then, we apply the standard analysis to derive the polytropic index. We explore the accuracy of the derived polytropic index for a range of uncertainties in the modeled density and temperature and repeat for various polytropic indices. Our analysis shows that the uncertainties in the plasma density introduce a systematic error in the determination of the polytropic index which can lead to artificial isothermal relations, while the uncertainties in the plasma temperature increase the statistical error of the calculated polytropic index value. We analyze Wind spacecraft observations of the solar wind protons and we derive the polytropic index in selected intervals over 2002. The derived polytropic index is affected by the plasma measurement uncertainties, in a similar way as predicted by our model. Finally, we suggest a new data-analysis approach, based on a physical constraint, that reduces the amount of erroneous derivations.

scholarly journals Effects of the Background Turbulence on the Relaxation of Ion Temperature Anisotropy in Space Plasmas

2021 ◽  
Vol 9 ◽  
Author(s):  
Pablo S. Moya ◽  
Roberto E. Navarro
Keyword(s):  
Solar Wind ◽  
Power Law ◽  
Large Scale ◽  
Wave Spectrum ◽  
Collisionless Plasma ◽  
Space Plasmas ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Background Spectrum ◽  
Background Magnetic Field

Turbulence in space plasmas usually exhibits two regimes separated by a spectral break that divides the so called inertial and kinetic ranges. Large scale magnetic fluctuations are dominated by non-linear MHD wave-wave interactions following a −5/3 or −2 slope power-law spectrum. After the break, at scales in which kinetic effects take place, the magnetic spectrum follows a steeper power-law k−α shape given by a spectral index α &gt; 5/3. Despite its ubiquitousness, the possible effects of a turbulent background spectrum in the quasilinear relaxation of solar wind temperatures are usually not considered. In this work, a quasilinear kinetic theory is used to study the evolution of the proton temperatures in an initially turbulent collisionless plasma composed by cold electrons and bi-Maxwellian protons, in which electromagnetic waves propagate along a background magnetic field. Four wave spectrum shapes are compared with different levels of wave intensity. We show that a sufficient turbulent magnetic power can drive stable protons to transverse heating, resulting in an increase in the temperature anisotropy and the reduction of the parallel proton beta. Thus, stable proton velocity distribution can evolve in such a way as to develop kinetic instabilities. This may explain why the constituents of the solar wind can be observed far from thermodynamic equilibrium and near the instability thresholds.

scholarly journals Estimating the Polytropic Indices of Plasmas with Partial Temperature Tensor Measurements: Application to Solar Wind Protons at ~1 au

2021 ◽  
Vol 11 (9) ◽  
pp. 4019
Author(s):  
Georgios Nicolaou ◽  
George Livadiotis ◽  
Mihir I. Desai
Keyword(s):  
Solar Wind ◽  
Solar Wind Plasma ◽  
Polytropic Index ◽  
Temperature Anisotropy ◽  
Polytropic Equation ◽  
Interaction Regions ◽  
Index Value ◽  
Full Temperature ◽  
The Relationship ◽  
The Magnetic Field

We examine the relationships between temperature tensor elements and their connection to the polytropic equation, which describes the relationship between the plasma scalar temperature and density. We investigate the possibility to determine the plasma polytropic index by fitting the fluctuations of temperature either perpendicular or parallel to the magnetic field. Such an application is particularly useful when the full temperature tensor is not available from the observations. We use solar wind proton observations at ~1 au to calculate the correlations between the temperature tensor elements and the scalar temperature. Our analysis also derives the polytropic equation in selected streamlines of solar wind plasma proton observations that exhibit temperature anisotropies related to stream-interaction regions. We compare the polytropic indices derived by fitting fluctuations of the scalar, perpendicular, and parallel temperatures, respectively. We show that the use of the parallel or perpendicular temperature, instead of the scalar temperature, still accurately derives the true, average polytropic index value, but only for a certain level of temperature anisotropy variability within the analyzed streamlines. The use of the perpendicular temperature leads to more accurate calculations, because its correlation with the scalar temperature is less affected by the anisotropy fluctuations.

scholarly journals Effects of the Background Turbulence on the Relaxation of Ion Temperature Anisotropy in Space Plasmas

2021 ◽  
Author(s):  
Pablo S Moya ◽  
Roberto E Navarro
Keyword(s):  
Solar Wind ◽  
Power Law ◽  
Large Scale ◽  
Wave Spectrum ◽  
Space Plasmas ◽  
Linear Wave ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Background Spectrum ◽  
Background Magnetic Field

&lt;p&gt;Turbulence in space plasmas usually exhibits two regimes separated by a spectral break that divides the so called inertial and kinetic ranges. Large scale magnetic fluctuations are dominated by MHD non-linear wave-wave interactions following a -5/3 or -3/2 slope power-law spectrum. After the break, at scales in which kinetic effects take place, the magnetic spectrum follows a steeper power-law &lt;em&gt;k&lt;sup&gt;- &amp;#945;&lt;/sup&gt;&lt;/em&gt; shape given by a spectral index &lt;em&gt;&amp;#945; &lt;/em&gt;&gt; 5/3. The location of the break and the particular value of &lt;em&gt;&amp;#945;, &lt;/em&gt;depend on plasma conditions, and different space environments can exhibit different spectral indices. Despite its ubiquitousness, the possible effects of a turbulent background spectrum in the quasilinear relaxation of solar wind temperatures are usually not considered. In this work, a quasilinear kinetic theory is used to study the evolution of the proton temperatures in a solar wind-like plasma composed by cold electrons and bi-Maxwellian protons, in which electromagnetic waves propagate along a background magnetic field. Four wave spectrum shapes are compared with different levels of wave intensity. We show that a sufficient turbulent magnetic power can drive stable protons to transverse heating, resulting in an increase in the temperature anisotropy and the reduction of the parallel proton beta. Thus, stable proton velocity distribution can evolve in such a way as to develop kinetic instabilities. This may explain why the constituents of the solar wind can be observed far from thermodynamic equilibrium and near the instability thresholds.&lt;/p&gt;

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