Anisotropy in solar wind plasma turbulence

A review of spectral anisotropy and variance anisotropy for solar wind fluctuations is given, with the discussion covering inertial range and dissipation range scales. For the inertial range, theory, simulations and observations are more or less in accord, in that fluctuation energy is found to be primarily in modes with quasi-perpendicular wavevectors (relative to a suitably defined mean magnetic field), and also that most of the fluctuation energy is in the vector components transverse to the mean field. Energy transfer in the parallel direction and the energy levels in the parallel components are both relatively weak. In the dissipation range, observations indicate that variance anisotropy tends to decrease towards isotropic levels as the electron gyroradius is approached; spectral anisotropy results are mixed. Evidence for and against wave interpretations and turbulence interpretations of these features will be discussed. We also present new simulation results concerning evolution of variance anisotropy for different classes of initial conditions, each with typical background solar wind parameters.

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Multi-spacecraft measurement of anisotropic power levels and scaling in solar wind turbulence

Annales Geophysicae ◽

10.5194/angeo-27-3019-2009 ◽

2009 ◽

Vol 27 (8) ◽

pp. 3019-3025 ◽

Cited By ~ 29

Author(s):

K. T. Osman ◽

T. S. Horbury

Keyword(s):

Solar Wind ◽

Spectral Index ◽

Mean Field ◽

Structure Functions ◽

Inertial Range ◽

Order Structure ◽

Parallel Direction ◽

The Mean ◽

Time Lagged ◽

Turbulent Cascade

Abstract. Measurements by the four Cluster spacecraft in the solar wind are used to determine quantitatively the field-aligned anisotropy of magnetohydrodynamic inertial range turbulence power levels and spectral indexes. We find, using time-lagged second order structure functions, that the spectral index is near 2 around the field-parallel direction, which is consistent with a "critical balance" turbulent cascade. Solar wind fluctuations are found to be anisotropic with power mainly in wavevectors perpendicular to the mean field, where the spectral index is around 5/3.

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Geometry of Magnetic Fluctuations near the Sun from the Parker Solar Probe

The Astrophysical Journal ◽

10.3847/1538-4357/ac3486 ◽

2021 ◽

Vol 923 (2) ◽

pp. 193

Author(s):

R. Bandyopadhyay ◽

D. J. McComas

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Large Scale ◽

Inertial Range ◽

Local Magnetic Field ◽

The Sun ◽

Magnetic Fluctuations ◽

Outer Scale ◽

Degree Of Anisotropy ◽

Dissipation Range

Abstract Solar wind magnetic fluctuations exhibit anisotropy due to the presence of a mean magnetic field in the form of the Parker spiral. Close to the Sun, direct measurements were not available until the recently launched Parker Solar Probe (PSP) mission. The nature of the anisotropy and geometry of the magnetic fluctuations play a fundamental role in dissipation processes and in the transport of energetic particles in space. Using PSP data, we present measurements of the geometry and anisotropy of the inner heliosphere magnetic fluctuations, from fluid to kinetic scales. The results are surprising and different from 1 au observations. We find that fluctuations evolve characteristically with size scale. However, unlike 1 au solar wind, at the outer scale, the fluctuations are dominated by wavevectors quasi-parallel to the local magnetic field. In the inertial range, average wavevectors become less field aligned, but still remain more field aligned than near-Earth solar wind. In the dissipation range, the wavevectors become almost perpendicular to the local magnetic field in the dissipation range, to a much higher degree than those indicated by 1 au observations. We propose that this reduced degree of anisotropy in the outer scale and inertial range is due to the nature of large-scale forcing outside the solar corona.

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Effects of the Solar Wind Conditions on Mercury's Exosphere: Hybrid Simulations

10.5194/egusphere-egu2020-13020 ◽

2020 ◽

Author(s):

Pavel M. Travnicek ◽

Dave Schriver ◽

Thomas Orlando ◽

James A. Slavin

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Interplanetary Magnetic Field ◽

Dynamic Pressure ◽

Energy Levels ◽

Solar Wind Plasma ◽

Deposited Energy ◽

Solar Wind Parameters ◽

Primary Focus ◽

Hybrid Simulations

<pre class="western">We carry out a set of global hybrid simulations of the Mercury's magnetosphere with the interplanetary magnetic field oriented in the desired directions. We study effects of changes of different solar wind parameters on the structure of the plasma circulation within Mercury&#8217;s magnetosphere. We focus our study on the changes caused by changes in the orientation of the interplanetary magnetic field and the dynamic pressure (velocity) of the solar wind. We study the structure of the of the Mercury&#8217;s magnetosphere under different solar wind conditions. Our primary focus is the assessment of the precipitation levels of solar wind hydrogen on the Mercury's surface (the amount, the deposited energy, its spectra and angular distribution) and on the formation of Mercury's exosphere. We examine density fluxes, energy levels and spectra of protons precipitating on Mercury&#8217;s surface as a function of longitude and altitude. It has been established, that Mercury has a plasma belt formed by quasi-trapped solar wind plasma close to the Mercury&#8217;s surface. Charged particles trapped in the belt mostly circle Mercury 1-2 times before they either precipitate on Mercury&#8217;s surface or escape into the Mercury&#8217;s magnetospheric cavity. Lower dynamic pressure of the solar wind pushes magnetopause up above the Mercury&#8217;s surface and the plasma belt has more space to develop. Its interaction with Mercury&#8217;s surface and dynamics under different solar wind conditions is essential on the precipitation of the plasma on the Mercury&#8217;s surface. Higher dynamic pressure of the solar wind can push the bow shock towards Mercury&#8217;s surface and make the surface open to the direct impact of the solar wind on the Mercury&#8217;s surface. Due to weak magnetic moment of the Mercury&#8217;s magnetosphere, the plasma environment at Mercury is very dynamic.</pre>

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Spectral evolution of Alfvénic turbulence

10.5194/egusphere-egu21-9861 ◽

2021 ◽

Author(s):

Roland Grappin ◽

Andrea Verdini ◽

Wolf-Christian Müller

Keyword(s):

Solar Wind ◽

Initial Conditions ◽

Coronal Holes ◽

Mean Field ◽

Polar Regions ◽

Spectral Evolution ◽

Mhd Turbulence ◽

Mhd Simulations ◽

The Mean ◽

Inner Heliosphere

Alfv&#233;nic turbulence denotes a regime of MHD turbulence in which Alfv&#233;n waves propagating in a given direction along the mean field are dominant, as commonly found in polar regions/coronal holes/fast solar wind.&#160;Generalization to Alfv&#233;nic turbulence of the Iroshnikov-Kraichnan (IK) weak theory concluded that one should observe a time increase of the imbalance between both Alfv&#233;n species and observe the so-called &#8220;spectral pinning&#8221;, i.e., steep spectra (with spectral index m+>3/2) for the dominant energy E+ and flat spectra (with index m-<3/2) for the sub-dominant energy E-.Since then, observations in the inner heliosphere have shown on the contrary a decrease of imbalance with time, with both species showing the same flat spectra (m&#177;&#160;&#8594; -3/2) when imbalance is large.We show here using direct MHD simulations that both behaviors may occur, the control parameters being the solar wind expansion rate as well as initial conditions of the plasma close to the Sun.

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Nonlinear electromagnetic wave interactions in Hall–MHD plasmas

Journal of Plasma Physics ◽

10.1017/s0022377810000486 ◽

2010 ◽

Vol 76 (6) ◽

pp. 893-901

Author(s):

DASTGEER SHAIKH ◽

P. K. SHUKŁA

Keyword(s):

Solar Wind ◽

Electromagnetic Wave ◽

Three Dimensional ◽

Solar Wind Plasma ◽

Inertial Range ◽

High Time Resolution ◽

Plasma Energy ◽

Frequency Regime ◽

Electromagnetic Wave Interactions ◽

Hall Mhd

AbstractWe have developed a massively parallelized fully three-dimensional (3D) compressible Hall–magnetohydrodynamic (MHD) code to investigate inertial range electromagnetic wave cascades and dissipative processes in the regime, where characteristic length scales associated with plasma fluctuations are smaller than ion gyroradii. Such regime is ubiquitously present in the solar wind and many other collisionless space plasmas. Particularly, in the solar wind, the high time resolution databases depict a spectral break near the end of the 5/3 spectrum that corresponds to a high-frequency regime where the electromagnetic turbulent cascades cannot be explained by the usual MHD models. This refers to a second inertial range, where turbulent cascades follow a k−7/3 (where k is a wavenumber) spectrum in which the characteristic electromagnetic fluctuations evolve typically on kinetic Alfvén time scales. In this paper, we describe results from our 3D compressible Hall–MHD simulations that explain the observed k−7/3 spectrum in the solar wind plasma, energy cascade, anisotropy, and other spectral features.

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Spectral anisotropy of solar wind turbulence in the inertial range and dissipation range

10.1063/1.3395817 ◽

2010 ◽

Cited By ~ 4

Author(s):

J. J. Podesta ◽

M. Maksimovic ◽

K. Issautier ◽

N. Meyer-Vernet ◽

M. Moncuquet ◽

...

Keyword(s):

Solar Wind ◽

Inertial Range ◽

Solar Wind Turbulence ◽

Wind Turbulence ◽

Dissipation Range

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ESR STUDY OF SPIN-HAMILTONIAN PARAMETERS AND CRYSTAL FIELD ENERGY LEVELS FOR THE LOW C3 SYMMETRY Fe3+ CENTER IN GREEN SAPPHIRE CRYSTALS AND POWDER

Modern Physics Letters B ◽

10.1142/s0217984907012505 ◽

2007 ◽

Vol 21 (04) ◽

pp. 225-236 ◽

Cited By ~ 2

Author(s):

P. LIMSUWAN ◽

N. UDOMKAN ◽

P. WINOTAI

Keyword(s):

Rotation Angle ◽

Energy Levels ◽

Heat Treating ◽

Esr Spectra ◽

Field Energy ◽

Hamiltonian Matrix ◽

Magnetic Field Direction ◽

Spin Hamiltonian ◽

Corundum Structure ◽

Hamiltonian Parameters

In this report, Fe 3+ impurity ions present in green sapphire ( Al 2 O 3) were studied experimentally, by heating a light green sapphire in flowing oxygen atmosphere for 12 h from 1200, 1300, 1400, 1500 and 1600°C, respectively. Electron spin resonance (ESR) spectra in X-band (~9.45 GHz ) were recorded by mounting the crystal with the c-axis perpendicular (θ = 90°) to the magnetic field direction. The spectra were recorded and simulated by a numerical diagonalization of spin Hamiltonian matrix in the range from 0 to 180 degrees for every 15 degrees of rotation angle (φ). In our case, only the last two sets of peaks strongly depend on the rotation angle (φ), and each exhibits C 3 symmetry due to two magnetically inequivalent Fe 3+ sites in the corundum structure. For polycrystalline ESR spectra, seven main Fe 3+ ESR absorption peaks occur at the resonance magnetic fields of 100.20, 310.24, 486.80, 525.00, 550.60, 761.00 and 777.00 mT respectively. Specifically, ESR signals show that the number of paramagnetic Fe 3+ ions increase roughly linearly with the heat treating temperature, having the [Formula: see text] ratio ~1.41 at 1600°C.

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A review of the SCOSTEP’s 5-year scientific program VarSITI—Variability of the Sun and Its Terrestrial Impact

Progress in Earth and Planetary Science ◽

10.1186/s40645-021-00410-1 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Kazuo Shiokawa ◽

Katya Georgieva

Keyword(s):

Solar Wind ◽

Interplanetary Space ◽

Solar Wind Plasma ◽

The Sun ◽

Scientific Program ◽

Solar Cycles ◽

Grand Minimum ◽

The Earth ◽

Earth Connection ◽

Near Future

AbstractThe Sun is a variable active-dynamo star, emitting radiation in all wavelengths and solar-wind plasma to the interplanetary space. The Earth is immersed in this radiation and solar wind, showing various responses in geospace and atmosphere. This Sun–Earth connection variates in time scales from milli-seconds to millennia and beyond. The solar activity, which has a ~11-year periodicity, is gradually declining in recent three solar cycles, suggesting a possibility of a grand minimum in near future. VarSITI—variability of the Sun and its terrestrial impact—was the 5-year program of the scientific committee on solar-terrestrial physics (SCOSTEP) in 2014–2018, focusing on this variability of the Sun and its consequences on the Earth. This paper reviews some background of SCOSTEP and its past programs, achievements of the 5-year VarSITI program, and remaining outstanding questions after VarSITI.

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Reflection-driven magnetohydrodynamic turbulence in the solar atmosphere and solar wind

Journal of Plasma Physics ◽

10.1017/s0022377819000540 ◽

2019 ◽

Vol 85 (4) ◽

Cited By ~ 13

Author(s):

Benjamin D. G. Chandran ◽

Jean C. Perez

Keyword(s):

Solar Wind ◽

Heating Rate ◽

Three Dimensional ◽

Power Spectra ◽

Inertial Range ◽

Magnetic Flux Tube ◽

Analytic Model ◽

Mhd Turbulence ◽

Background Magnetic Field ◽

Turbulent Heating

We present three-dimensional direct numerical simulations and an analytic model of reflection-driven magnetohydrodynamic (MHD) turbulence in the solar wind. Our simulations describe transverse, non-compressive MHD fluctuations within a narrow magnetic flux tube that extends from the photosphere, through the chromosphere and corona and out to a heliocentric distance $r$ of 21 solar radii $(R_{\odot })$ . We launch outward-propagating ‘ $\boldsymbol{z}^{+}$ fluctuations’ into the simulation domain by imposing a randomly evolving photospheric velocity field. As these fluctuations propagate away from the Sun, they undergo partial reflection, producing inward-propagating ‘ $\boldsymbol{z}^{-}$ fluctuations’. Counter-propagating fluctuations subsequently interact, causing fluctuation energy to cascade to small scales and dissipate. Our analytic model incorporates dynamic alignment, allows for strongly or weakly turbulent nonlinear interactions and divides the $\boldsymbol{z}^{+}$ fluctuations into two populations with different characteristic radial correlation lengths. The inertial-range power spectra of $\boldsymbol{z}^{+}$ and $\boldsymbol{z}^{-}$ fluctuations in our simulations evolve toward a $k_{\bot }^{-3/2}$ scaling at $r>10R_{\odot }$ , where $k_{\bot }$ is the wave-vector component perpendicular to the background magnetic field. In two of our simulations, the $\boldsymbol{z}^{+}$ power spectra are much flatter between the coronal base and $r\simeq 4R_{\odot }$ . We argue that these spectral scalings are caused by: (i) high-pass filtering in the upper chromosphere; (ii) the anomalous coherence of inertial-range $\boldsymbol{z}^{-}$ fluctuations in a reference frame propagating outwards with the $\boldsymbol{z}^{+}$ fluctuations; and (iii) the change in the sign of the radial derivative of the Alfvén speed at $r=r_{\text{m}}\simeq 1.7R_{\odot }$ , which disrupts this anomalous coherence between $r=r_{\text{m}}$ and $r\simeq 2r_{\text{m}}$ . At $r>1.3R_{\odot }$ , the turbulent heating rate in our simulations is comparable to the turbulent heating rate in a previously developed solar-wind model that agreed with a number of observational constraints, consistent with the hypothesis that MHD turbulence accounts for much of the heating of the fast solar wind.

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