TAUS measurements of non-gyrotropic distribution functions of solar wind alpha particles

1996 ◽  
Author(s):  
H. F. Astudillo ◽  
E. Marsch ◽  
S. Livi ◽  
H. Rosenbauer
Keyword(s):  
Solar Wind ◽  
Distribution Functions ◽  
Alpha Particles

Study of alpha particle properties across rarefaction regions

2021 ◽  
Author(s):  
Tereza Durovcova ◽  
Jana Šafránková ◽  
Zdeněk Němeček
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Alpha Particle ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
Distribution Functions ◽  
Alpha Particles ◽  
Slow Solar Wind ◽  
The Sun ◽  
Wind Source

<p>Two large-scale interaction regions between the fast solar wind emanating from coronal holes and the slow solar wind coming from streamer belt are usually distinguished. When the fast stream pushes up against the slow solar wind ahead of it, a compressed interaction region that co-rotates with the Sun (CIR) is created. It was already shown that the relative abundance of alpha particles, which usually serve as one of solar wind source identifiers can change within this region. By symmetry, when the fast stream outruns the slow stream, a corotating rarefaction region (CRR) is formed. CRRs are characterized by a monotonic decrease of the solar wind speed, and they are associated with the regions of small longitudinal extent on the Sun. In our study, we use near-Earth measurements complemented by observations at different heliocentric distances, and focus on the behavior of alpha particles in the CRRs because we found that the large variations of the relative helium abundance (AHe) can also be observed there. Unlike in the CIRs, these variations are usually not connected with the solar wind speed and alpha-proton relative drift changes. We thus apply a superposed-epoch analysis of identified CRRs with a motivation to determine the global profile of alpha particle parameters through these regions. Next, we concentrate on the cases with largest AHe variations and investigate whether they can be associated with the changes of the solar wind source region or whether there is a relation between the AHe variations and the non-thermal features in the proton velocity distribution functions like the temperature anisotropy and/or presence of the proton beam.</p>

scholarly journals Hybrid Vlasov simulations for alpha particles heating in the solar wind

2010 ◽  
Vol 6 (S274) ◽  
pp. 168-171
Author(s):  
Denise Perrone ◽  
Francesco Valentini ◽  
Pierluigi Veltri
Keyword(s):  
Solar Wind ◽  
Physical Space ◽  
Low Noise ◽  
Space Physics ◽  
Distribution Functions ◽  
Alpha Particles ◽  
Theoretical Problem ◽  
Direction Parallel ◽  
Background Magnetic Field ◽  
Kinetic Effects

AbstractHeating and acceleration of heavy ions in the solar wind and corona represent a long-standing theoretical problem in space physics and are distinct experimental signatures of kinetic processes occurring in collisionless plasmas. To address this problem, we propose the use of a low-noise hybrid-Vlasov code in four dimensional phase space (1D in physical space and 3D in velocity space) configuration. We trigger a turbulent cascade injecting the energy at large wavelengths and analyze the role of kinetic effects along the development of the energy spectra. Following the evolution of both proton and α distribution functions shows that both the ion species significantly depart from the maxwellian equilibrium, with the appearance of beams of accelerated particles in the direction parallel to the background magnetic field.

scholarly journals Alpha particle thermodynamics in the inner heliosphere fast solar wind

2019 ◽  
Vol 623 ◽  
pp. L2 ◽  
Author(s):  
D. Stansby ◽  
D. Perrone ◽  
L. Matteini ◽  
T. S. Horbury ◽  
C. S. Salem
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Alpha Particle ◽  
Distribution Functions ◽  
Alpha Particles ◽  
Perpendicular Direction ◽  
The Sun ◽  
Fast Solar Wind ◽  
Field Parallel ◽  
The Magnetic Field

Context. Plasma processes occurring in the corona and solar wind can be probed by studying the thermodynamic properties of different ion species. However, most in situ observations of positive ions in the solar wind are taken at 1 AU, where information on their solar source properties may have been irreversibly erased. Aims. In this study we aim to use the properties of alpha particles at heliocentric distances between 0.3 AU and 1 AU to study plasma processes occurring at the points of observation, and to infer processes occurring inside 0.3 AU by comparing our results to previous remote sensing observations of the plasma closer to the Sun. Methods. We reprocessed the original Helios positive ion distribution functions, isolated the alpha particle population, and computed the alpha particle number density, velocity, and magnetic field perpendicular and parallel temperatures. We then investigated the radial variation of alpha particle temperatures in fast solar wind observed between 0.3 AU and 1 AU. Results. Between 0.3 AU and 1 AU alpha particles are heated in the magnetic field perpendicular direction and cooled in the magnetic field parallel direction. Alpha particle evolution is bounded by the alpha firehose instability threshold, which provides one possible mechanism to explain the observed parallel cooling and perpendicular heating. Closer to the Sun our observations suggest that the alpha particles undergo heating in the perpendicular direction, whilst the large magnetic field parallel temperatures observed at 0.3 AU may be due to the combined effect of double adiabatic expansion and alpha particle deceleration inside 0.3 AU.

Proton Beam Abundance Variations and Their Relation to Alpha Particle Properties

2021 ◽  
Vol 923 (2) ◽  
pp. 170
Author(s):  
Tereza Ďurovcová ◽  
Jana Šafránková ◽  
Zdeněk Němeček
Keyword(s):  
Solar Wind ◽  
Proton Beam ◽  
Alpha Particle ◽  
Source Region ◽  
Radial Distance ◽  
Alpha Particles ◽  
Momentum Balance ◽  
Particle Interactions ◽  
Coulomb Collisions ◽  
Particle Properties

Abstract Less abundant but still dynamically important solar wind components are the proton beam and alpha particles, which usually contribute similarly to the total ion momentum. The main characteristics of alpha particles are determined by the solar wind source region, but the origin of the proton beam and its properties are still not fully explained. We use the plasma data measured in situ on the path from 0.3 to 1 au (Helios 1 and 2) and focus on the proton beam development with an increasing radial distance as well as on the connection between the proton beam and alpha particle properties. We found that the proton beam relative abundance increases with increasing distance from the Sun in the collisionally young streams. Among the mechanisms suggested for beam creation, we have identified the wave–particle interactions with obliquely propagating Alfvén modes being consistent with observations. As the solar wind streams get collisionally older, the proton beam decay gradually dominates and the beam abundance is reduced. In search for responsible mechanisms, we found that the content of alpha particles is correlated with the proton beam abundance, and this effect is more pronounced in the fast solar wind streams during the solar maximum. We suggest that Coulomb collisions are the main agent leading to merging of the proton beam and core. We are also showing that the variations of the proton beam abundance are correlated with a decrease of the alpha particle velocity in order to maintain the total momentum balance in the solar wind frame.

Tsallis Distribution Functions in the Solar Wind: Magnetic Field and Velocity Observations

2007 ◽  
Author(s):  
Leonard F. Burlaga ◽  
Adolfo F. Viñas ◽  
Sumiyoshi Abe ◽  
Hans Herrmann ◽  
Piero Quarati ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Distribution Functions ◽  
Solar Wind Magnetic Field ◽  
Tsallis Distribution

scholarly journals Ion-driven Instabilities in the Inner Heliosphere. I. Statistical Trends

2021 ◽  
Vol 923 (1) ◽  
pp. 116
Author(s):  
Mihailo M. Martinović ◽  
Kristopher G. Klein ◽  
Tereza Ďurovcová ◽  
Benjamin L. Alterman
Keyword(s):  
Solar Wind ◽  
Particle Interaction ◽  
Radial Distance ◽  
Solar Wind Plasma ◽  
Distribution Functions ◽  
Nyquist Criterion ◽  
Velocity Distribution Functions ◽  
Instability Growth ◽  
Statistical Trends ◽  
The Impact

Abstract Instabilities described by linear theory characterize an important form of wave–particle interaction in the solar wind. We diagnose unstable behavior of solar wind plasma between 0.3 and 1 au via the Nyquist criterion, applying it to fits of ∼1.5M proton and α particle Velocity Distribution Functions (VDFs) observed by Helios I and II. The variation of the fraction of unstable intervals with radial distance from the Sun is linear, signaling a gradual decline in the activity of unstable modes. When calculated as functions of the solar wind velocity and Coulomb number, we obtain more extreme, exponential trends in the regions where collisions appear to have a notable influence on the VDF. Instability growth rates demonstrate similar behavior, and significantly decrease with Coulomb number. We find that for a nonnegligible fraction of observations, the proton beam or secondary component might not be detected, due to instrument resolution limitations, and demonstrate that the impact of this issue does not affect the main conclusions of this work.

Analysis of Alfvénic flows with Solar Orbiter: particle and magnetic observations down to kinetic scales.

2021 ◽  
Author(s):  
Philippe Louarn ◽  
Andrei fedorov ◽  
alexis Rouillard ◽  
Benoit Lavraud ◽  
Vincent Génot ◽  
...  
Keyword(s):  
Solar Wind ◽  
Fine Structure ◽  
Time Resolution ◽  
Time Scale ◽  
Residual Energy ◽  
Distribution Functions ◽  
Strongly Correlated ◽  
Temperature Anisotropy ◽  
Velocity Fluctuations ◽  
Turbulence Parameters

<p>The magnetic and velocity fluctuations of the solar wind may be strongly correlated. This characterizes the  ‘Alfvenic’ flows. Using the observations of the Proton Alfa sensor (PAS/SWA) and the magnetometer (MAG) onboard Solar Orbiter, we analyze a period of 100 hours of such alfvenic flows, at different scales. Several parameters of the turbulence are computed (V-B correlation, various spectral indexes, cross-helicity, residual energy). We explore how these parameters may vary with time and characterize different turbulent states of the flow. More specifically, using the unprecedented time resolution of PAS during burst mode, especially its capability to measure 3D distribution functions at time scale below the proton gyroperiod, we study the connection of the turbulence to the dissipation domain and analyze the fine structure of the distribution functions and their evolutions at sub-second scales. The goal is to investigate whether some characteristics of the distributions, as their more or less pronounced temperature anisotropy, may be related to the turbulence parameters and the degree of V-B correlation.</p>

A Global Survey of Geospace Electrons with eVlasiator: First Results

2021 ◽  
Author(s):  
Markku Alho ◽  
Markus Battarbee ◽  
Yann Pfau-Kempf ◽  
Urs Ganse ◽  
Lucile Turc ◽  
...  
Keyword(s):  
Solar Wind ◽  
Spatial Resolution ◽  
Kinetic Models ◽  
Electron Distribution ◽  
State Of The Art ◽  
Distribution Functions ◽  
Upper Atmosphere ◽  
Electron Precipitation ◽  
Gas Dynamic ◽  
First Results

<div> <p>Models of the geospace plasma environment have been proceeding towards more realistic descriptions of the solar wind—magnetosphere interaction, from gas-dynamic to MHD and hybrid ion-kinetic models such as the state-of-the-art Vlasiator model. Advances in computational capabilities have enabled global simulations of detailed physics, but the electron scale has so far been out of reach in a truly global setting. </p> </div><div> <p>In this work we present results from eVlasiator, an offshoot of the Vlasiator model, showing first results from a global 2D+3V kinetic electron geospace simulation. Despite truncation of some electron physics and use of ion-scale spatial resolution, we show that realistic electron distribution functions are obtainable within the magnetosphere and describe these in relation to MMS observations. Electron precipitation to the upper atmosphere from these velocity distributions is estimated.</p> </div>

Ion energy and momentum flux near the cometopause of Comet 67P/Churyumov-Gerasimenko

2021 ◽  
Author(s):  
Hayley Williamson ◽  
Hans Nilsson ◽  
Anja Moslinger ◽  
Sofia Bergman ◽  
Gabriella Stenberg-Wieser
Keyword(s):  
Solar Wind ◽  
Complex Dynamics ◽  
Distribution Functions ◽  
Transitional Period ◽  
Ion Energy ◽  
Rosetta Mission ◽  
Before And After ◽  
Composition Analyzer ◽  
Energy And Momentum ◽  
Comet 67P

<p>Defined as the region where the plasma interaction region of a comet goes from being solar wind-dominated to cometary ion-dominated, the cometopause is a region of comingling plasmas and complex dynamics. The Rosetta mission orbited comet 67P/Churyumov-Gerasimenko for roughly two years. During this time, the cometopause was observed by the Ion Composition Analyzer (ICA), part of the Rosetta Plasma Consortium (RPC), before and after the spacecraft was in the solar wind ion cavity, defined as the region where no solar wind ions were measured. Data from ICA shows that solar wind and cometary ions have similar momentum and energy flux moments during this transitional period, indicating mass loading and deflection of the solar wind. We examine higher order moments and distribution functions for the solar wind and cometary species between December 2015 and March 2016. The behavior of the solar wind protons indicates that in many cases these protons are deflected in a sunward direction, while the cometary ions continue to move predominately antisunward. By studying the distribution functions of the protons during these time periods, it is possible to see a non-Maxwellian energy distribution. This can inform on the nature of the cometopause boundary and the energy transfer mechanisms at play in this region.</p>

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