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

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.

Download Full-text

Evolution of the MHD turbulence properties in the inner heliosphere with the PSP/SolO alignment data

10.5194/egusphere-egu21-14585 ◽

2021 ◽

Author(s):

Daniele Telloni ◽

Keyword(s):

Solar Wind ◽

High Frequency ◽

Interplanetary Space ◽

Solar Wind Plasma ◽

Radial Dependence ◽

Physical Processes ◽

Temperature Anisotropy ◽

Mhd Turbulence ◽

Radial Evolution ◽

Inner Heliosphere

<p>Radial alignments between pairs of spacecraft is the only way to observationally investigate the turbulent evolution of the solar wind as it expands throughout interplanetary space. On September 2020 Parker Solar Probe (PSP) and Solar Orbiter (SolO) were nearly perfectly radially aligned, with PSP orbiting around its perihelion at 0.1 au (and crossing the nominal Alfv&#233;n point) and SolO at 1 au. PSP/SolO joint observations of the same solar wind plasma allow the extraordinary and unprecedented opportunity to study how the turbulence properties of the solar wind evolve in the inner heliosphere over the wide distance of 0.9 au. The radial evolution of (i) the MHD properties (such as radial dependence of low- and high-frequency breaks, compressibility, Alfv&#233;nic content of the fluctuations), (ii) the polarization status, (iii) the presence of wave modes at kinetic scale as well as their distribution in the plasma instability-temperature anisotropy plane are just few instances of what can be addressed. Of furthest interest is the study of whether and how the cascade transfer and dissipation rates evolve with the solar distance, since this has great impact on the fundamental plasma physical processes related to the heating of the solar wind. In this talk I will present some of the results obtained by exploiting the PSP/SolO alignment data.</p>

Download Full-text

Dynamical evolution of the inner heliosphere approaching solar activity maximum: interpreting Ulysses observations using a global MHD model

Annales Geophysicae ◽

10.5194/angeo-21-1347-2003 ◽

2003 ◽

Vol 21 (6) ◽

pp. 1347-1357 ◽

Cited By ~ 17

Author(s):

P. Riley ◽

Z. Mikić ◽

J. A. Linker

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Maximum ◽

Dynamical Evolution ◽

Solar Wind Plasma ◽

Polar Regions ◽

Activity Maximum ◽

Interplanetary Magnetic Fields ◽

Interplanetary Physics ◽

Interaction Regions

Abstract. In this study we describe a series of MHD simulations covering the time period from 12 January 1999 to 19 September 2001 (Carrington Rotation 1945 to 1980). This interval coincided with: (1) the Sun’s approach toward solar maximum; and (2) Ulysses’ second descent to the southern polar regions, rapid latitude scan, and arrival into the northern polar regions. We focus on the evolution of several key parameters during this time, including the photospheric magnetic field, the computed coronal hole boundaries, the computed velocity profile near the Sun, and the plasma and magnetic field parameters at the location of Ulysses. The model results provide a global context for interpreting the often complex in situ measurements. We also present a heuristic explanation of stream dynamics to describe the morphology of interaction regions at solar maximum and contrast it with the picture that resulted from Ulysses’ first orbit, which occurred during more quiescent solar conditions. The simulation results described here are available at: http://sun.saic.com.Key words. Interplanetary physics (Interplanetary magnetic fields; solar wind plasma; sources of the solar wind)

Download Full-text

Proton Temperature-anisotropy Instability Coexisting with Ambient Turbulence in the Solar-wind Plasma

The Astrophysical Journal ◽

10.3847/1538-4357/ab0f9d ◽

2019 ◽

Vol 875 (2) ◽

pp. 125 ◽

Cited By ~ 1

Author(s):

S. A. Markovskii ◽

Bernard J. Vasquez ◽

Benjamin D. G. Chandran

Keyword(s):

Solar Wind ◽

Solar Wind Plasma ◽

Temperature Anisotropy ◽

Proton Temperature ◽

Ambient Turbulence

Download Full-text

Cluster-C1 observations on the geometrical structure of linear magnetic holes in the solar wind at 1 AU

Annales Geophysicae ◽

10.5194/angeo-28-1695-2010 ◽

2010 ◽

Vol 28 (9) ◽

pp. 1695-1702 ◽

Cited By ~ 27

Author(s):

T. Xiao ◽

Q. Q. Shi ◽

T. L. Zhang ◽

S. Y. Fu ◽

L. Li ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Geometrical Structure ◽

Occurrence Rate ◽

Geometrical Shape ◽

Magnetic Field Data ◽

Magnetic Field Magnitude ◽

The Relationship ◽

Plasma Measurements ◽

The Magnetic Field

Abstract. Interplanetary linear magnetic holes (LMHs) are structures in which the magnetic field magnitude decreases with little change in the field direction. They are a 10–30% subset of all interplanetary magnetic holes (MHs). Using magnetic field and plasma measurements obtained by Cluster-C1, we surveyed the LMHs in the solar wind at 1 AU. In total 567 interplanetary LMHs are identified from the magnetic field data when Cluster-C1 was in the solar wind from 2001 to 2004. We studied the relationship between the durations and the magnetic field orientations, as well as that of the scales and the field orientations of LMHs in the solar wind. It is found that the geometrical structure of the LMHs in the solar wind at 1 AU is consistent with rotational ellipsoid and the ratio of scales along and across the magnetic field is about 1.93:1. In other words, the structure is elongated along the magnetic field at 1 AU. The occurrence rate of LMHs in the solar wind at 1 AU is about 3.7 per day. It is shown that not only the occurrence rate but also the geometrical shape of interplanetary LMHs has no significant change from 0.72 AU to 1 AU in comparison with previous studies. It is thus inferred that most of interplanetary LMHs observed at 1 AU are formed and fully developed before 0.72 AU. The present results help us to study the formation mechanism of the LMHs in the solar wind.

Download Full-text

Solar Wind ∼0.15–1.5 keV Electrons around Corotating Interaction Regions at 1 au

The Astrophysical Journal ◽

10.3847/1538-4357/ac2505 ◽

2021 ◽

Vol 922 (2) ◽

pp. 198

Author(s):

Jiawei Tao ◽

Linghua Wang ◽

Gang Li ◽

Robert F. Wimmer-Schweingruber ◽

Chadi Salem ◽

...

Keyword(s):

Solar Wind ◽

Solar Wind Speed ◽

Kinetic Temperature ◽

Number Density ◽

Kappa Index ◽

Corotating Interaction Regions ◽

Fast Wind ◽

Magnetic Field Magnitude ◽

Interaction Regions ◽

The Relationship

Abstract Here we present a statistical study of the ∼0.15–1.5 keV suprathermal electrons observed in uncompressed/compressed slow and fast solar wind around 59 corotating interaction regions (CIRs) with good measurements by Wind 3DP from 1995 through 1997. For each of these CIRs, we fit the strahl and halo energy spectra at ∼0.15–1.5 keV to a Kappa function with a Kappa index κ and kinetic temperature T eff. We find that the ∼0.15–1.5 keV strahl electrons behave similarly in both slow and fast wind: the strahl number density n s positively correlates with the solar wind electron temperature T e and interplanetary magnetic field magnitude ∣B∣, while the strahl pitch angle width Θ s decreases with the solar wind speed V sw. These suggest that the strahl electrons are generated by a similar/same process at the Sun in both slow and fast wind that produces these correlations, and the scattering efficiency of strahl in the interplanetary medium (IPM) decreases with V sw. The ∼0.15–1.5 keV halo electrons also behave similarly in both slow and fast wind: the halo parameter positively correlates with the corresponding strahl parameter, and the halo number density n h positively correlates only with T e . These indicate that the halo formation process in the IPM retains most of the strahl properties, but it erases the relationship between n s and ∣B∣. In addition, κ in compressed wind distributes similarly to that in uncompressed wind, for both the strahl and halo. It shows that CIRs at 1 au are not a significant/effective acceleration source for the strahl and halo.

Download Full-text

Observation of three distinct ion populations at the Kelvin-Helmholtz-unstable magnetopause

Annales Geophysicae ◽

10.5194/angeo-26-1559-2008 ◽

2008 ◽

Vol 26 (6) ◽

pp. 1559-1566 ◽

Cited By ~ 21

Author(s):

M. G. G. T. Taylor ◽

B. Lavraud

Keyword(s):

Boundary Layer ◽

Solar Wind ◽

Solar Wind Plasma ◽

Double Star ◽

Single Event ◽

Helmholtz Instability ◽

Temperature Anisotropy ◽

Low Latitude ◽

Solar Wind Origin ◽

Unambiguous Conclusion

Abstract. We report Double Star spacecraft observations of the dusk-flank magnetopause and its boundary layer under predominantly northward interplanetary magnetic field (IMF). Under such conditions the flank low-latitude boundary layers (LLBL) of the magnetosphere are known to broaden. The primary candidate processes associated with the transport of solar wind plasma into the LLBL are: (1) local diffusive plasma transport associated with the Kelvin-Helmholtz instability (KHI), (2) local plasma penetration owing to magnetic reconnection in the vicinity of the KHI-driven vortices, and (3) via a pre-existing boundary layer formed through double high-latitude reconnection on the dayside. Previous studies have shown that a cold population of solar wind origin is typically mixed with a hot population of magnetospheric origin in the LLBL. The present observations show the coexistence of three distinct ion populations in the dusk LLBL, during an interval when the magnetopause is unstable to the KHI: (1) a typical hot magnetospheric population, (2) a cold population that shows parallel temperature anisotropy, and (3) a distinct third cold population that shows perpendicular temperature anisotropy. Although no unambiguous conclusion may be drawn from this single event, we discuss the possible mechanisms at work and the origin of each population by envisaging three likely sources: hot magnetospheric plasma sheet, cold magnetosheath of solar wind origin, and cold plasma of ionospheric origin.

Download Full-text

Combined electron firehose and electromagnetic ion cyclotron instabilities: quasilinear approach

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2916 ◽

2020 ◽

Vol 499 (1) ◽

pp. 659-667

Author(s):

Z Ali ◽

M Sarfraz ◽

P H Yoon

Keyword(s):

Solar Wind ◽

Dynamical Evolution ◽

Solar Wind Plasma ◽

Distribution Functions ◽

Temperature Anisotropy ◽

Spatial And Temporal Scales ◽

Proton Temperature ◽

Ion Cyclotron ◽

Velocity Distribution Functions ◽

High Beta

ABSTRACT Various plasma waves and instabilities are abundantly present in the solar wind plasma, as evidenced by spacecraft observations. Among these, propagating modes and instabilities driven by temperature anisotropies are known to play a significant role in the solar wind dynamics. In situ measurements reveal that the threshold conditions for these instabilities adequately explain the solar wind conditions at large heliocentric distances. This paper pays attention to the combined effects of electron firehose instability driven by excessive parallel electron temperature anisotropy (T⊥e < T∥e) at high beta conditions, and electromagnetic ion cyclotron instability driven by excessive perpendicular proton temperature anisotropy (T⊥i > T∥i). By employing quasilinear kinetic theory based upon the assumption of bi-Maxwellian velocity distribution functions for protons and electrons, the dynamical evolution of the combined instabilities and their mutual interactions mediated by the particles is explored in depth. It is found that while in some cases, the two unstable modes are excited and saturated at distinct spatial and temporal scales, in other cases, the two unstable modes are intermingled such that a straightforward interpretation is not so easy. This shows that when the dynamics of protons and electrons are mutually coupled and when multiple unstable modes are excited in the system, the dynamical consequences can be quite complex.

Download Full-text

Solar wind temperature anisotropy and its influence on the spectrum of turbulence

10.5194/egusphere-egu2020-2738 ◽

2020 ◽

Author(s):

Alexander Pitňa ◽

Jana Šafránkova ◽

Zdeněk Němeček

Keyword(s):

Solar Wind ◽

Large Scale ◽

Power Spectra ◽

Solar Wind Plasma ◽

Turbulent Medium ◽

Thermal Velocity ◽

Temperature Anisotropy ◽

Ion Density ◽

Proton Temperature ◽

Wind Spacecraft

<p>Nearly collisionless solar wind plasma originating in the solar corona is a turbulent medium. The energy within large scale fluctuations is continuously transferred into smaller scales and it eventually reaches scales at which it is converted into a random particle motion, thus heating the plasma. Although the processes that take place within this complex system have been studied for decades, many questions remain unresolved. The power spectra of the fluctuating fields of the magnetic field, bulk velocity, and ion density were studied extensively; however, the spectrum of the thermal velocity is seldom reported and/or discussed. In this paper, we address the difficulty of estimating its power spectrum. We analyze high-cadence (31 ms) thermal velocity measurements of the BMSW instrument onboard the Spektr-R spacecraft and the SWE instrument onboard the Wind spacecraft. We discuss the role of the proton temperature anisotropy (parallel/perpendicular) and its influence on the shape of the power spectra in the inertial range of turbulence.</p>

Download Full-text

Long-Term Independence of Solar Wind Polytropic Index on Plasma Flow Speed

Entropy ◽

10.3390/e20100799 ◽

2018 ◽

Vol 20 (10) ◽

pp. 799 ◽

Cited By ~ 14

Author(s):

George Livadiotis

Keyword(s):

Solar Wind ◽

Plasma Flow ◽

Solar Wind Speed ◽

Solar Wind Plasma ◽

Flow Speed ◽

Polytropic Index ◽

Solar Cycles ◽

Solar Wind Proton ◽

Plasma Flow Speed

The paper derives the polytropic indices over the last two solar cycles (years 1995–2017) for the solar wind proton plasma near Earth (~1 AU). We use ~92-s datasets of proton plasma moments (speed, density, and temperature), measured from the Solar Wind Experiment instrument onboard Wind spacecraft, to estimate the moving averages of the polytropic index, as well as their weighted means and standard errors as a function of the solar wind speed and the year of measurements. The derived long-term behavior of the polytropic index agrees with the results of other previous methods. In particular, we find that the polytropic index remains quasi-constant with respect to the plasma flow speed, in agreement with earlier analyses of solar wind plasma. It is shown that most of the fluctuations of the polytropic index appear in the fast solar wind. The polytropic index remains quasi-constant, despite the frequent entropic variations. Therefore, on an annual basis, the polytropic index of the solar wind proton plasma near ~1 AU can be considered independent of the plasma flow speed. The estimated all-year weighted mean and its standard error is γ = 1.86 ± 0.09.

Download Full-text