Power spectral density of magnetic field and ion velocity fluctuations from inertial to kinetic ranges

The solar wind is a unique laboratory to study the turbulent processes occurring in a collisionless plasma with high Reynolds numbers. A turbulent cascade&#8212;the process that transfers the free energy contained within the large scale fluctuations into the smaller ones&#8212;is believed to be one of the most important mechanisms responsible for heating of the solar corona and solar wind. The paper analyzes power spectra of solar wind velocity, density and magnetic field fluctuations that are computed in the frequency range around the break between inertial and kinetic scales. The study uses measurements of the Bright Monitor of the Solar Wind (BMSW) on board the Spektr-R spacecraft with a time resolution of 32 ms complemented with 10 Hz magnetic field observations from the Wind spacecraft propagated to the Spektr-R location. The statistics based on more than 42,000 individual spectra show that: (1) the spectra of both quantities can be fitted by two (three in the case of the density) power-law segments; (2) the median slopes of parallel and perpendicular fluctuation velocity and magnetic field components are different; (3) the break between MHD and kinetic scales as well as the slopes are mainly controlled by the ion beta parameter. These experimental results are compared with high-resolution 2D hybrid particle-in-cell simulations, where the electrons are considered to be a massless, charge-neutralizing fluid with a constant temperature, whereas the ions are described as macroparticles representing portions of their distribution function. In spite of several limitations (lack of the electron kinetics, lower dimensionality), the model results agree well with the experimental findings. Finally, we discuss differences between observations and simulations in relation to the role of important physical parameters in determining the properties of the turbulent cascade.

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Numerical simulation of ion reflection by lunar crustal magnetic fields

10.5194/egusphere-egu2020-18137 ◽

2020 ◽

Author(s):

Andrey Divin ◽

Jan Deca ◽

Charles Lue ◽

Roman Beliaev

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Large Scale ◽

Field Measurements ◽

Distribution Functions ◽

Three Dimensions ◽

Lunar Crust ◽

Ion Distribution ◽

Particle In Cell ◽

Reflection Model

We investigate the dynamics of solar wind - Moon interaction by means of large-scale Particle-in-Cell (PIC) simulations in this study. Implicit moment PIC method and open boundaries are implemented in the code (iPIC3D) allowing to use large-scale domains in three dimensions. Even though the Moon has no global dipolar magnetic field, satellite magnetic field measurements at low-altitude (8-80 km) orbits discovered the presence of patches of intense remanent magnetization of the lunar crust. In order to simulate the scattering effect of the lunar remanent magnetic field we implemented an empirical proton reflection model based on low-attitude survey by the Chandrayaan-1 spacecraft [Lue, 2011]. In this study we focus on the day side effects only and thus do not resolve wake and limb effects. Reflected ions are found to create an energized population of particles in the solar wind and are responsible for sub-ion scale instabilities over the strongest anomalies with non-Maxwellian ion distribution functions.

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HelioSwarm: The Nature of Turbulence in Space Plasmas

10.5194/egusphere-egu21-12092 ◽

2021 ◽

Author(s):

Harlan Spence ◽

Kristopher Klein ◽

HelioSwarm Science Team

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Large Scale ◽

Solar Wind Plasma ◽

Turbulent Energy ◽

Space Plasmas ◽

Plasma Parameters ◽

Astrophysical Plasmas ◽

Ion Distributions ◽

Background Magnetic Field

Recently selected for phase A study for NASA&#8217;s Heliophysics MidEx Announcement of Opportunity, the HelioSwarm Observatory proposes to transform our understanding of the physics of turbulence in space and astrophysical plasmas by deploying nine spacecraft to measure the local plasma and magnetic field conditions at many points, with separations between the spacecraft spanning MHD and ion scales.&#160;&#160;HelioSwarm resolves the transfer and dissipation of turbulent energy in weakly-collisional magnetized plasmas with a novel configuration of spacecraft in the solar wind. These simultaneous multi-point, multi-scale measurements of space plasmas allow us to reach closure on two science goals comprised of six science objectives: (1) reveal how turbulent energy is transferred in the most probable, undisturbed solar wind plasma and distributed as a function of scale and time; (2) reveal how this turbulent cascade of energy varies with the background magnetic field and plasma parameters in more extreme solar wind environments; (3) quantify the transfer of turbulent energy between fields, flows, and ion heat; (4) identify thermodynamic impacts of intermittent structures on ion distributions; (5) determine how solar wind turbulence affects and is affected by large-scale solar wind structures; and (6) determine how strongly driven turbulence differs from that in the undisturbed solar wind.&#160;

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Plasma and Magnetic Field Turbulence in the Earth’s Magnetosheath at Ion Scales

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2020.616635 ◽

2021 ◽

Vol 7 ◽

Author(s):

Liudmila Rakhmanova ◽

Maria Riazantseva ◽

Georgy Zastenker

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Wind Plasma ◽

Bow Shock ◽

Present Review ◽

Wind Effects ◽

Earth’S Bow Shock ◽

Magnetic Field Turbulence ◽

Plasma Measurements ◽

Turbulent Cascade

Crossing the Earth’s bow shock is known to crucially affect solar wind plasma including changes in turbulent cascade. The present review summarizes results of more than 15 years of experimental exploration into magnetosheath turbulence. Great contributions to understanding turbulence development inside the magnetosheath was made by means of recent multi-spacecraft missions. We introduce the main results provided by them together with first observations of the turbulent cascade based on direct plasma measurements by the Spektr-R spacecraft in the magnetosheath. Recent results on solar wind effects on turbulence in the magnetosheath are also discussed.

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A Turbulent Heliosheath Driven by Rayleigh Taylor Instability

10.21203/rs.3.rs-198925/v1 ◽

2021 ◽

Author(s):

Merav Opher ◽

James Drake ◽

Gary Zank ◽

Gabor Toth ◽

Erick Powell ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Large Scale ◽

Neutral Atom ◽

Solar Magnetic Field ◽

Characteristic Time Scale ◽

Rayleigh Taylor Instability ◽

Scale Turbulence ◽

Magnetohydrodynamic Simulations ◽

Rt Instability

Abstract The heliosphere is the bubble formed by the solar wind as it interacts with the interstellar medium (ISM). Studies show that the solar magnetic field funnels the heliosheath solar wind (the shocked solar wind at the edge of the heliosphere) into two jet-like structures1-2. Magnetohydrodynamic simulations show that these heliospheric jets become unstable as they move down the heliotail1,3 and drive large-scale turbulence. However, the mechanism that produces of this turbulence had not been identified. Here we show that the driver of the turbulence is the Rayleigh-Taylor (RT) instability caused by the interaction of neutral H atoms streaming from the ISM with the ionized matter in the heliosheath (HS). The drag between the neutral and ionized matter acts as an effective gravity which causes a RT instability to develop along the axis of the HS magnetic field. A density gradient exists perpendicular to this axis due to the confinement of the solar wind by the solar magnetic field. The characteristic time scale of the instability depends on the neutral H density in the ISM and for typical values the growth rate is ~ 3 years. The instability destroys the coherence of the heliospheric jets and magnetic reconnection ensues, allowing ISM material to penetrate the heliospheric tail. Signatures of this instability should be observable in Energetic Neutral Atom (ENA) maps from future missions such as IMAP4. The turbulence driven by the instability is macroscopic and potentially has important implications for particle acceleration.

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Ion-scale break of the plasma fluctuation spectra in different large-scale solar wind streams

10.5194/egusphere-egu21-13569 ◽

2021 ◽

Author(s):

Maria Riazantseva ◽

Liudmila Rakhmanova ◽

Yuri Yermolaev ◽

Irina Lodkina ◽

Georgy Zastenker ◽

...

Keyword(s):

Solar Wind ◽

Large Scale ◽

Plasma Heating ◽

Coronal Holes ◽

Magnetic Clouds ◽

Alfven Wave ◽

Slow Solar Wind ◽

P Value ◽

High Temporal Resolution ◽

Turbulent Cascade

Appearance of measurements of the interplanetary medium parameters with high temporal resolution gave rise to a variety of investigations of turbulent cascade at ion kinetic scales at which processes of plasma heating was believed to operate. Our recent studies based on high frequency plasma measurements at Spektr-R spacecraft have shown that the turbulent cascade was not stable and dynamically changed depending on the plasma conditions in different large-scale solar wind structures. These changes was most significant at the kinetic scales of the turbulent cascade. Slow undisturbed solar wind was characterized by the consistency of the spectra to the predictions of the kinetic Alfven wave turbulence model. On the other hand, the discrepancy between the model predictions and registered spectra were found in stream interaction regions characterized by crucial steepening of spectra at the kinetic scales with slopes having values up to -(4-5). This discrepancy was clearly shown for plasma compression region Sheath in front of the magnetic clouds and CIR in front of high speed streams associated with coronal holes. Present study is focused on the break preceding the kinetic scales. Currently the characteristic plasma parameters associated with the formation of the break is still debated. Number of studies demonstrated that the break was consistent with distinct characteristic frequencies for different values &#8203;&#8203;of the plasma proton parameter beta &#946;p. Present study consider the ratio between the break frequency determined for ion flux fluctuation spectra according to Spektr-R data and several characteristic plasma frequencies used traditionally in such cases. The value of this ratio is statistically compared for different large-scale solar wind streams. We analyze both the classical spectrum view with two slopes and one break and the spectrum with flattening between magnetohydrodynamic and kinetic scales.&#160; Our results show that for the Sheath and CIR regions characterized typically by &#946;p &#8804;1 the break corresponds statistically to the frequency determined by the proton gyroradius. At the same time such correspondence are not observed either for the undisturbed slow solar wind with similar &#946;p value or for disturbed flows associated with interplanetary manifestations of coronal mass ejections, where &#946;p << 1. The results also shows that in slow undisturbed solar wind the break is closer to the frequency determined by the inertial proton length. Thus, apparently the transition between streams of different speeds may result in the change of dissipation regimes and plays role in plasma heating at these areas. This work was supported by the RFBR grant No. 19-02-00177a

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Particle-In-Cell simulations of resonant interactions between whistler waves and electrons in the near-Sun solar wind: scattering of the strahl into the halo and heat flux regulation.

10.5194/egusphere-egu21-10198 ◽

2021 ◽

Author(s):

Alfredo Micera ◽

Andrei Zhukov ◽

Rodrigo A. López ◽

Maria Elena Innocenti ◽

Marian Lazar ◽

...

Keyword(s):

Magnetic Field ◽

Heat Flux ◽

Solar Wind ◽

Velocity Distribution ◽

Pitch Angle ◽

Electron Velocity ◽

Magnetic Field Direction ◽

Whistler Waves ◽

Electron Velocity Distribution ◽

Particle In Cell

Electron velocity distribution functions, initially composed of core and strahl populations as typically encountered in the near-Sun solar wind and as recently observed by Parker Solar Probe, have been modeled via fully kinetic Particle-In-Cell simulations. It has been demonstrated that, as a consequence of the evolution of the electron velocity distribution function, two branches of the whistler heat flux instability can be excited, which can drive whistler waves propagating in the direction parallel or oblique to the background magnetic field. First, the strahl undergoes pitch-angle scattering with oblique whistler waves, which provokes the reduction of the strahl drift velocity and the simultaneous broadening of its pitch angle distribution. Moreover, the interaction with the oblique whistler waves results in the scattering towards higher perpendicular velocities of resonant strahl electrons and in the appearance of a suprathermal halo population which, at higher energies, deviates from the Maxwellian distribution. Later on, the excited whistler waves shift towards smaller angles of propagation and secondary scattering processes with quasi-parallel whistler waves lead to a redistribution of the scattered particles into a more symmetric halo. All processes are accompanied by a significant decrease of the heat flux carried by the strahl population along the magnetic field direction, although the strongest heat flux rate decrease is simultaneous with the propagation of the oblique whistler waves.

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Statistical analysis of the dependence of large-scale Birkeland currents on solar wind parameters

Annales Geophysicae ◽

10.5194/angeo-28-515-2010 ◽

2010 ◽

Vol 28 (2) ◽

pp. 515-530 ◽

Cited By ~ 35

Author(s):

H. Korth ◽

B. J. Anderson ◽

C. L. Waters

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Mach Number ◽

Electric Field ◽

Large Scale ◽

Dynamic Pressure ◽

Dominant Factor ◽

Total Current ◽

Current Densities ◽

Birkeland Currents

Abstract. The spatial distributions of large-scale field-aligned Birkeland currents have been derived using magnetic field data obtained from the Iridium constellation of satellites from February 1999 to December 2007. From this database, we selected intervals that had at least 45% overlap in the large-scale currents between successive hours. The consistency in the current distributions is taken to indicate stability of the large-scale magnetosphere–ionosphere system to within the spatial and temporal resolution of the Iridium observations. The resulting data set of about 1500 two-hour intervals (4% of the data) was sorted first by the interplanetary magnetic field (IMF) GSM clock angle (arctan(By/Bz)) since this governs the spatial morphology of the currents. The Birkeland current densities were then corrected for variations in EUV-produced ionospheric conductance by normalizing the current densities to those occurring for 0° dipole tilt. To determine the dependence of the currents on other solar wind variables for a given IMF clock angle, the data were then sorted sequentially by the following parameters: the solar wind electric field in the plane normal to the Earth–Sun line, Eyz; the solar wind ram pressure; and the solar wind Alfvén Mach number. The solar wind electric field is the dominant factor determining the Birkeland current intensities. The currents shift toward noon and expand equatorward with increasing solar wind electric field. The total current increases by 0.8 MA per mV m−1 increase in Eyz for southward IMF, while for northward IMF it is nearly independent of the electric field, increasing by only 0.1 MA per mV m−1 increase in Eyz. The dependence on solar wind pressure is comparatively modest. After correcting for the solar dynamo dependencies in intensity and distribution, the total current intensity increases with solar wind dynamic pressure by 0.4 MA/nPa for southward IMF. Normalizing the Birkeland current densities to both the median solar wind electric field and dynamic pressure effects, we find no significant dependence of the Birkeland currents on solar wind Alfvén Mach number.

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Is there a left-handed magnetic field in the solar neighborhood?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833961 ◽

2019 ◽

Vol 621 ◽

pp. A97 ◽

Cited By ~ 8

Author(s):

A. Bracco ◽

S. Candelaresi ◽

F. Del Sordo ◽

A. Brandenburg

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Power Spectra ◽

Field Structure ◽

Solar Neighborhood ◽

Galactic Magnetic Field ◽

Polarization Data ◽

Left Handed ◽

Cross Correlations

Context. The analysis of the full-sky Planck polarization data at 850 μm revealed unexpected properties of the E- and B-mode power spectra of dust emission in the interstellar medium (ISM). The positive cross-correlations over a wide range of angular scales between the total dust intensity, T, and both E and (most of all) B modes has raised new questions about the physical mechanisms that affect dust polarization, such as the Galactic magnetic field structure. This is key both to better understanding ISM dynamics and to accurately describing Galactic foregrounds to the polarization of the cosmic microwave background (CMB). In particular, in the quest to find primordial B modes of the CMB, the observed positive cross-correlation between T and B for interstellar dust requires further investigation towards parity-violating processes in the ISM. Aims. In this theoretical paper we investigate the possibility that the observed cross-correlations in the dust polarization power spectra, and specifically the one between T and B, can be related to a parity-odd quantity in the ISM such as the magnetic helicity. Methods. We produce synthetic dust polarization data, derived from 3D analytical toy models of density structures and helical magnetic fields, to compare with the E and B modes of observations. We present several models. The first is an ideal fully helical isotropic case, such as the Arnold-Beltrami-Childress field. Second, following the nowadays favored interpretation of the T–E signal in terms of the observed alignment between the magnetic field morphology and the filamentary density structure of the diffuse ISM, we design models for helical magnetic fields wrapped around cylindrical interstellar filaments. Lastly, focusing on the observed T–B correlation, we propose a new line of interpretation of the Planck observations advocating the presence of a large-scale helical component of the Galactic magnetic field in the solar neighborhood. Results. Our analysis shows that: I) the sign of magnetic helicity does not affect E and B modes for isotropic magnetic-field configurations; II) helical magnetic fields threading interstellar filaments cannot reproduce the Planck results; and III) a weak helical left-handed magnetic field structure in the solar neighborhood may explain the T–B correlation seen in the Planck data. Such a magnetic-field configuration would also account for the observed large-scale T–E correlation. Conclusions. This work suggests a new perspective for the interpretation of the dust polarization power spectra that supports the imprint of a large-scale structure of the Galactic magnetic field in the solar neighborhood.

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Structure of a collisionless pair jet in a magnetized electron–proton plasma: flow-aligned magnetic field

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834393 ◽

2019 ◽

Vol 621 ◽

pp. A142 ◽

Cited By ~ 9

Author(s):

M. E. Dieckmann ◽

D. Folini ◽

I. Hotz ◽

A. Nordman ◽

P. Dell’Acqua ◽

...

Keyword(s):

Magnetic Field ◽

Collisionless Plasma ◽

Mean Velocity ◽

Ambient Plasma ◽

Particle In Cell ◽

Flow Energy ◽

Pair Plasma ◽

Background Magnetic Field ◽

Order Of Magnitude ◽

Uniform Background

Aims. We study the effect a guiding magnetic field has on the formation and structure of a pair jet that propagates through a collisionless electron–proton plasma at rest. Methods. We model with a particle-in-cell (PIC) simulation a pair cloud with a temperature of 400 keV and a mean speed of 0.9c (c - light speed). Pair particles are continuously injected at the boundary. The cloud propagates through a spatially uniform, magnetized, and cool ambient electron–proton plasma at rest. The mean velocity vector of the pair cloud is aligned with the uniform background magnetic field. The pair cloud has a lateral extent of a few ion skin depths. Results. A jet forms in time. Its outer cocoon consists of jet-accelerated ambient plasma and is separated from the inner cocoon by an electromagnetic piston with a thickness that is comparable to the local thermal gyroradius of jet particles. The inner cocoon consists of pair plasma, which lost its directed flow energy while it swept out the background magnetic field and compressed it into the electromagnetic piston. A beam of electrons and positrons moves along the jet spine at its initial speed. Its electrons are slowed down and some positrons are accelerated as they cross the head of the jet. The latter escape upstream along the magnetic field, which yields an excess of megaelectronvolt positrons ahead of the jet. A filamentation instability between positrons and protons accelerates some of the protons, which were located behind the electromagnetic piston at the time it formed, to megaelectronvolt energies. Conclusions. A microscopic pair jet in collisionless plasma has a structure that is similar to that predicted by a hydrodynamic model of relativistic astrophysical pair jets. It is a source of megaelectronvolt positrons. An electromagnetic piston acts as the contact discontinuity between the inner and outer cocoons. It would form on subsecond timescales in a plasma with a density that is comparable to that of the interstellar medium in the rest frame of the latter. A supercritical fast magnetosonic shock will form between the pristine ambient plasma and the jet-accelerated plasma on a timescale that exceeds our simulation time by an order of magnitude.

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Comparison of the observed dependence of large-scale Birkeland currents on solar wind parameters with that obtained from global simulations

Annales Geophysicae ◽

10.5194/angeo-29-1809-2011 ◽

2011 ◽

Vol 29 (10) ◽

pp. 1809-1826 ◽

Cited By ~ 17

Author(s):

H. Korth ◽

L. Rastätter ◽

B. J. Anderson ◽

A. J. Ridley

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Large Scale ◽

Coupled Model ◽

Total Current ◽

Modeling Framework ◽

Rate Of Increase ◽

Solar Wind Parameters ◽

The University ◽

Birkeland Currents

Abstract. Spatial distributions of the large-scale Birkeland currents derived from magnetic field data acquired by the constellation of Iridium Communications satellites have been compared with global-magnetosphere magneto-hydrodynamic (MHD) simulations. The Iridium data, spanning the interval from February 1999 to December 2007, were first sorted into 45°-wide bins of the interplanetary magnetic field (IMF) clock angle, and the dependencies of the Birkeland currents on solar wind electric field magnitude, Eyz, ram pressure, psw, and Alfvén Mach number, MA, were then examined within each bin. The simulations have been conducted at the publicly-accessible Community Coordinated Modeling Center using the University of Michigan Space Weather modeling Framework, which features a global magnetosphere model coupled to the Rice Convection Model. In excess of 120 simulations with steady-state conditions were executed to yield the dependencies of the Birkeland currents on the solar wind and IMF parameters of the coupled model. Averaged over all IMF orientations, the simulation reproduces the Iridium statistical Birkeland current distributions with a two-dimensional correlation coefficient of about 0.8, and the total current agrees with the climatology averages to within 10%. The total current for individual events regularly exceeds those computed from statistical distributions by factors of ≥2, resulting in larger disparities between observations and simulations. The simulation results also qualitatively reflect the observed increases in total current with increasing Eyz and psw, but the model underestimates the rate of increase by up to 50%. The equatorward expansion and shift of the large-scale currents toward noon observed for increasing Eyz are also evident in the simulation current patterns. Consistent with the observations, the simulation does not show a significant dependence of the total current on MA.

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