A. A. Vidotto, V. Jatenco-Pereira
Alfven waves have been invoked as an important mechanism of particle acceleration in stellar winds of cool stars. After their identification in the solar wind they started to be studied in winds of stars located in different regions of the HR diagram. We discuss here some characteristics of these waves and we present a direct application in the acceleration of late-type stellar winds.
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We review our recent results of Alfven wave-driven winds. First, we present the result of a self-consistent 1D MHD simulations for solar winds from the photosphere to interplanetary region. Here, we emphasize the importance of the reflection of Alfven waves in the density stratified corona and solar winds. We also introduce the recent HINODE observation that might detect the reflection signature of transverse (Alfvenic) waves by Fujimura & Tsuneta (2009). Then, we show the results of Alfven wave-driven winds from red giant stars. We explain the change of the atmosphere properties from steady c…
M dwarf's atmosphere and wind is expected to be highly magnetized. The nonlinear propagation of Alfvén wave could play a key role in both heating the stellar atmosphere and driving the stellar wind. Along this Alfvén wave scenario, we carried out the one-dimensional compressive magnetohydrodynamic (MHD) simulation about the nonlinear propagation of Alfvén wave from the M dwarf's photosphere, chromosphere to the corona and interplanetary space. Based on the simulation results, we develop the semi-empirical method describing the solar and M dwarf's coronal temperature, stellar wind velocity, and…
We study the formation and evolution of a turbulent spectrum of Alfvén waves driven by reflection off the solar wind density gradients, starting from the coronal base up to 17 solar radii, well beyond the Alfvénic critical point. The background solar wind is assigned and 2D shell models are used to describe nonlinear interactions. We find that the turbulent spectra are influenced by the nature of reflected waves. Close to the base, these give rise to a flatter and steeper spectrum for the outgoing and reflected waves respectively. At higher heliocentric distance both spectra evolve toward an a…
Alfvén waves are responsible for the transfer of magnetic energy in the magnetized plasma. They are involved in heating solar atmosphere and driving solar wind through various nonlinear processes. Since the magnetic field configurations directly affect the nonlinearity of Alfvén waves, it is important to investigate how they relate to the solar atmosphere and wind structure through the nonlinear propagation of Alfvén waves. In this study, we carried out the one-dimensional magnetohydrodynamic simulations to realize the above relation. The results show that when the nonlinearity of Alfvén waves…
M dwarf's atmosphere is expected to be highly magnetized. The magnetic energy can be responsible for heating the stellar chromosphere and corona, and driving the stellar wind. The nonlinear propagation of Alfvén wave is the promising mechanism for both heating stellar atmosphere and driving stellar wind. Based on this Alfvén wave scenario, we carried out the one-dimensional compressive magnetohydrodynamic (MHD) simulation to reproduce the stellar atmospheres and winds of TRAPPIST-1, Proxima Centauri, YZ CMi, AD Leo, AX Mic, as well as the Sun. The nonlinear propagation of Alfvén wave from the …
The solar wind emanates from the hot and tenuous solar corona. Earlier studies using 1.5 dimensional simulations show that Alfvén waves generated in the photosphere play an important role in coronal heating through the process of non-linear mode conversion. In order to understand the physics of coronal heating and solar wind acceleration together, it is important to consider the regions from photosphere to interplanetary space as a single system. We performed 2.5 dimensional, self-consistent magnetohydrodynamic simulations, covering from the photosphere to the interplanetary space for the firs…
Using one-dimensional numerical simulations, we study the elementary process of Alfvén wave reflection in a uniform medium, including nonlinear effects. In the linear regime, Alfvén wave reflection is triggered only by the inhomogeneity of the medium, whereas in the nonlinear regime, it can occur via nonlinear wave-wave interactions. Such nonlinear reflection (backscattering) is typified by decay instability. In most studies of decay instabilities, the initial condition has been a circularly polarized Alfvén wave. In this study we consider a linearly polarized Alfvén wave, which drives density…
The interaction between Alfven-wave turbulence and the background solar wind affects the cross helicity in two ways. Non-WKB reflection converts outward-propagating Alfven waves into inward-propagating Alfven waves and vice versa, and the turbulence transfers momentum to the background flow. When both effects are accounted for, the total cross helicity is conserved. In the special case that the background density and flow speed are independent of time, the equations of cross-helicity conservation and total-energy conservation can be combined to recover a well-known equation derived by Heineman…
We take stock of recent observations that identify the episodic plasma heating and injection of Alfvenic energy at the base of fast solar wind (in coronal holes). The plasma heating is associated with the occurrence of chromospheric spicules that leave the lower solar atmosphere at speeds of order 100km/s, the hotter coronal counterpart of the spicule emits radiation characteristic of root heating that rapidly reaches temperatures of the order of 1MK. Furthermore, the same spicules and their coronal counterparts ("Propagating Coronal Disturbances"; PCD) exhibit large amplitude, high speed, Alf…
We present numerical simulations of reduced magnetohydrodynamic (RMHD) turbulence in a magnetic flux tube at the center of a polar coronal hole. The model for the background atmosphere is a solution of the momentum equation, and includes the effects of wave pressure on the solar wind outflow. Alfvén waves are launched at the coronal base, and reflect at various heights due to variations in Alfvén speed and outflow velocity. The turbulence is driven by nonlinear interactions between the counter-propagating Alfvén waves. Results are presented for two models of the background atmosphere. In the f…
Observations of stellar rotation show that low-mass stars lose angular momentum during the main sequence. We simulate the winds of Sun-like stars with a range of rotation rates, covering the fast and slow magneto-rotator regimes, including the transition between the two. We generalize an Alfvén-wave driven solar wind model that builds on previous works by including the magneto-centrifugal force explicitly. In this model, the surface-averaged open magnetic flux is assumed to scale as $B_\ast f^{\rm open}_\ast \propto {\rm Ro}^{-1.2}$, where $f^{\rm open}_\ast$ and ${\rm Ro}$ are the surface ope…
We present the numerical simulations of winds from evolved giant stars using a fully non-linear, time dependent 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully non-linear MHD wind simulations to include a broadband frequency spectrum of Alfvén waves that drive winds from red giant stars. We calculated four Alfvén wind models that cover the whole range of Alfvén wave frequency spectrum to characterize the role of freely propagated and reflected Alfvén waves in the gravitationally stratified atmosphere of a late-type giant star. Our simulations demonstrate t…
We develop a magnetohydrodynamical model of Alfvén wave-driven wind in open magnetic flux tubes piercing the stellar surface of Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stars, and investigate the physical properties of the winds. The model simulations are carried out along the evolutionary tracks of stars with initial mass in the range of 1.5 to 3.0 $M_{\odot}$ and initial metallicity $Z_{\rm ini}$=0.02. The surface magnetic field strength being set to be 1G, we find that the wind during the evolution of star can be classified into the following four types; the first is the win…
Two of the central problems in our understanding of the solar chromosphere are how the upper chromosphere is heated and what drives spicules. Estimates of the required chromospheric heating, based on radiative and conductive losses suggest a rate of ${\sim} 0.1 \mathrm{\:erg\:cm^{-3}\:s^{-1}}$ in the lower chromosphere dropping to ${\sim} 10^{-3} \mathrm{\:erg\:cm^{-3}\:s^{-1}}$ in the upper chromosphere (\citet{Avrett1981}). The chromosphere is also permeated by spicules, higher density plasma from the lower atmosphere propelled upwards at speeds of ${\sim} 10-20 \mathrm{\:km\:s^{-1}}$, for s…
Line-driven stellar winds from massive (OB) stars are subject to a strong line-deshadowing instability. Recently, spectropolarimetric surveys have collected ample evidence that a subset of Galactic massive stars hosts strong surface magnetic fields. We investigate here the propagation and stability of magneto-radiative waves in such a magnetised, line-driven wind. Our analytic, linear stability analysis includes line-scattering from the stellar radiation, and accounts for both radial and non-radial perturbations. We establish a bridging law for arbitrary perturbation wavelength after which we …
Using numerical simulations, we investigate the onset and suppression of parametric decay instability (PDI) in the solar wind, focusing on the suppression effect by the wind acceleration and expansion. We also discuss the role of PDI in generating the density fluctuation in the solar wind and the cross-helicity evolution up to $1 {\rm \ au}$. Numerical simulations from the coronal base to 1 au are conducted in a self-consistent manner; we take into account the feedback of wave energy and pressure in the background. Monochromatic waves with various injection frequencies $f_0$ are injected to di…
Alfvén-wave-driven 3D magnetohydrodynamic (MHD) models, which are increasingly used to predict stellar wind properties, contain unconstrained parameters and rely on low-resolution stellar magnetograms. We explore the effects of the input Alfvén wave energy flux and the surface magnetogram on the wind properties predicted by the Alfvén Wave Solar Model (AWSoM). We lowered the resolution of two solar magnetograms during solar cycle maximum and minimum using spherical harmonic decomposition. The Alfvén wave energy was altered based on non-thermal velocities determined from a far ultraviolet (FUV)…
Here we investigate the contribution of surface Alfven wave damping to the heating of the solar wind in minima conditions. These waves are present in regions of strong inhomogeneities in density or magnetic field (e. g., the border between open and closed magnetic field lines). Using a 3-dimensional Magnetohydrodynamics (MHD) model, we calculate the surface Alfven wave damping contribution between 1-4 solar radii, the region of interest for both acceleration and coronal heating. We consider waves with frequencies lower than those that are damped in the chromosphere and on the order of those do…
The collisionless dissipation of anisotropic Alfvénic turbulence is a promising candidate to solve the solar wind heating problem. Extensive studies examined the kinetic properties of Alfvén waves in simple Maxwellian or bi-Maxwellian plasmas. However, the observed electron velocity distribution functions in the solar wind are more complex. In this study, we analyze the properties of kinetic Alfvén waves in a plasma with two drifting electron populations. We numerically solve the linearized Maxwell-Vlasov equations and find that the damping rate and the proton-electron energy partition for kin…
How the solar wind is accelerated to its supersonic speed is intimately related to how it is heated. Mechanisms based on ion-cyclotron resonance have been successful in explaining a large number of observations, those concerning the significant ion temperature anisotropy above coronal holes in particular. However, they suffer from the inconsistency with turbulence theory which says that the turbulent cascade in a low-beta medium like the solar corona should proceed in the perpendicular rather than the parallel direction, meaning that there is little energy in the ion gyro-frequency range for i…
We study the behaviour and properties of the solar wind using a 2.5D Alfvén wave driven wind model. We first systematically compare the results of an Alfvén wave (AW) driven wind model with a polytropic approach. Polytropic magnetohydrodynamic wind models are thermally driven, while Alfvén waves act as additional acceleration and heating mechanisms in the Alfvén wave driven model. We confirm that an AW-driven model is required to reproduce the observed bimodality of slow and fast solar winds. We are also able to reproduce the observed anti-correlation between the terminal wind velocity and the…
We conduct a three-dimensional magnetohydrodynamic (MHD) simulation of the parametric decay instability of Alfvén waves and resultant compressible MHD turbulence, which is likely to develop in the solar wind acceleration region. Because of the presence of the mean magnetic field, the nonlinear stage is characterized by filament-like structuring and anisotropic cascading. By calculating the timescales of phase mixing and the evolution of Alfvén wave turbulence, we have found that the early nonlinear stage is dominated by phase mixing, while the later phase is dominated by imbalanced Alfvén wave…
One proposed mechanism for heating the solar wind, from close to the sun to beyond 10 AU, invokes low-frequency, oblique, Alfven-wave turbulence. Because small-scale oblique Alfven waves (kinetic Alfven waves) are compressive, the measured density fluctuations in the solar wind place an upper limit on the amplitude of kinetic Alfven waves and hence an upper limit on the rate at which the solar wind can be heated by low-frequency, Alfvenic turbulence. We evaluate this upper limit for both coronal holes at 5 solar radii and in the near-Earth solar wind. At both radii, the upper limit we find is …
The measured spectrum of kinetic Alfven wave fluctuations in the turbulent solar wind plasma is used to calculate the electron and ion distribution functions resulting from quasi-linear diffusion. The modified ion distribution function is found to be unstable to long wavelength electromagnetic ion cyclotron waves. These waves pitch angle scatter the parallel ion velocity into perpendicular velocity which effectively increases the perpendicular ion temperature.
In the lower solar coronal regions where the magnetic field is dominant, the Alfven speed is much higher than the wind speed. In contrast, the near-Earth solar wind is strongly super-Alfvenic, i.e., the wind speed greatly exceeds the Alfven speed. The transition between these regimes is classically described as the "Alfven point" but may in fact occur in a distributed Alfven critical region. NASA's Parker Solar Probe (PSP) mission has entered this region, as it follows a series of orbits that gradually approach more closely to the sun. During its 8th and 9th solar encounters, at a distance of …
The slow solar wind exhibits strong variability on timescales from minutes to days, likely related to magnetic reconnection processes in the extended solar corona. Higginson2017b presented a numerical magnetohydrodynamic simulation which showed interchange magnetic reconnection is ubiquitous and most likely responsible for releasing much of the slow solar wind, in particular along topological features known as the Separatrix-Web (S-Web). Here, we continue our analysis, focusing on two specific aspects of structured slow solar wind variability. The first type is present in the slow solar wind f…
One of the most important early results from the Parker Solar Probe (PSP) is the ubiquitous presence of magnetic switchbacks, whose origin is under debate. Using a three-dimensional direct numerical simulation of the equations of compressible magnetohydrodynamics from the corona to 40 solar radii, we investigate whether magnetic switchbacks emerge from granulation-driven Alfvén waves and turbulence in the solar wind. The simulated solar wind is an Alfvénic slow-solar-wind stream with a radial profile consistent with various observations, including observations from PSP. As a natural consequenc…
We present a measurement of the energy carried and dissipated by Alfvén waves in a polar coronal hole. Alfvén waves have been proposed as the energy source that heats the corona and drives the solar wind. Previous work has shown that line widths decrease with height in coronal holes, which is a signature of wave damping, but have been unable to quantify the energy lost by the waves. This is because line widths depend on both the non-thermal velocity v_nt and the ion temperature T_i. We have implemented a means to separate the T_i and v_nt contributions using the observation that at low heights…
Averaging Effects on the Solar Wind Alfven Mach Number: Implications for Switchbacks and Alfven Transition
本研究利用帕克太阳探测器1至19次飞掠数据，探究平均时间尺度对太阳风阿尔文马赫数及湍流特性表征的影响，发现亚阿尔文区间分布对合适平均尺度不敏感，磁涨落能量随平均窗口增大而增加，相关时间随日心距离和MA减小而缩短，明确了选择物理意义背景对湍流参数表征的重要性。
Alfvén-wave turbulence has emerged as an important heating mechanism to accelerate the solar wind. The generation of this turbulent heating is dependent on the presence and subsequent interaction of counter-propagating alfvén waves. This requires us to understand the propagation and evolution of alfvén waves in the solar wind in order to develop an understanding of the relationship between turbulent heating and solar-wind parameters. We aim to study the response of the solar wind upon injecting monochromatic single-frequency alfvén waves at the base of the corona for various magnetic flux-tube…
The observed sub-proton scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quite-time suggest them as possible source of free energy to drive the turbulence. Using particle-in-cell simulations, we explore how free energy in energetic electrons, released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfvénic and whistler waves are excited that evolve through inverse and forward magnetic energy cascade…
We carry out two-dimensional magnetohydrodynamic (MHD) simulations of an ensemble of Alfvénic fluctuations propagating in a structured, expanding solar wind including the presence of fast and slow solar wind streams. Using an appropriate expanding box model, the simulations incorporate the effects of fast-slow stream shear and compression and rarefaction self-consistently. We investigate the radial and longitudinal evolution of the cross-helicity, the total and residual energies and the power spectra of outward and inward Alfvénic fluctuations. The stream interaction is found to strongly affec…
Effect of Magnetic diffusion in the Chromosphere on the Solar Wind
本文通过显式包含欧姆与双极扩散的MHD模拟，揭示色球层非理想磁扩散会衰减阿尔文波并降低日冕温度与太阳风质量损失率，而小幅增强光球速度扰动可恢复这些量。
We revisit the role of longitudinal waves in driving the solar wind. We study how the the $p$-mode-like vertical oscillation on the photosphere affects the properties of solar winds under the framework of Alfvén-wave-driven winds. We perform a series of one-dimensional magnetohydrodynamical numerical simulations from the photosphere to beyond several tens of solar radii. We find that the mass-loss rate drastically increases with the longitudinal wave amplitude at the photosphere up to $\sim 4$ times, in contrast to the classical understanding that the acoustic wave hardly affects the energetic…
Measurements and simulations of inertial compressive turbulence in the solar wind are characterized by anti-correlated magnetic fluctuations parallel to the mean field and density structures. This signature has been interpreted as observational evidence for non-propagating pressure balanced structures (PBS), kinetic ion acoustic waves, as well as the MHD slow-mode. Given the high damping rates of parallel propagating compressive fluctuations, their ubiquity in satellite observations is surprising, and suggestive of a local driving process. One possible candidate for the generation of compressi…
We study the role the the p-mode-like vertical oscillation on the photosphere in driving solar winds in the framework of Alfven-wave-driven winds. By performing one-dimensional magnetohydrodynamical numerical simulations from the photosphere to the interplanetary space, we discover that the mass-loss rate is raised up to 4 times as the amplitude of longitudinal perturbations at the photosphere increases. When the longitudinal fluctuation is added, transverse waves are generated by the mode conversion from longitudinal waves in the chromosphere, which increases Alfvenic Poynting flux in the cor…
Identifying the heating mechanisms of the solar corona and the driving mechanisms of solar wind are key challenges in understanding solar physics. A full three-dimensional compressible magnetohydrodynamic (MHD) simulation was conducted to distinguish between the heating mechanisms in the fast solar wind above the open field region. Our simulation describes the evolution of the Alfvénic waves, which includes the compressible effects from the photosphere to the heliospheric distance $s$ of 27 solar radii ($R_\odot$). The hot corona and fast solar wind were reproduced simultaneously due to the di…
We develop a 1D solar-wind model that includes separate energy equations for the electrons and protons, proton temperature anisotropy, collisional and collisionless heat flux, and an analytical treatment of low-frequency, reflection-driven, Alfven-wave turbulence. To partition the turbulent heating between electron heating, parallel proton heating, and perpendicular proton heating, we employ results from the theories of linear wave damping and nonlinear stochastic heating. We account for mirror and oblique firehose instabilities by increasing the proton pitch-angle scattering rate when the pro…
Estimating the Poynting flux of Alfvénic waves in polar coronal holes across Solar Cycle 24
本研究系统测量太阳活动周24期间极区冕洞阿尔芬波的垂直Poynting通量，发现其在整个活动周内基本恒定，表明波对太阳风能量贡献与活动周无显著相关。
Kinetic Alfven wave turbulence in solar wind is considered and it is shown that non-Maxwellian electron distribution function has a significant effect on the dynamics of the solar wind plasmas. Linear Landau damping leads to the formation of a plateau in the parallel electron distribution function which diminishes the Landau damping rate significantly. Nonlinear scattering of waves by plasma particles is generalized to short wavelengths and it is found that for the solar wind parameters this scattering is the dominant process as compared to three wave decay and coalescence in the wave vector r…
(Abridged) Turbulence in the solar wind is believed to generate an energy cascade that is supported primarily by Alfvén waves or Alfvénic fluctuations at MHD scales and by kinetic Alfvén waves (KAWs) at kinetic scales $k_\perp ρ_i\gtrsim 1$. Linear Landau damping of KAWs increases with increasing wavenumber and at some point the damping becomes so strong that the energy cascade is completely dissipated. A model of the energy cascade process that includes the effects of linear collisionless damping of KAWs and the associated compounding of this damping throughout the cascade process is used to …
Stellar Wind Driven Alfvén Wing Dynamics in Planetary and Exoplanetary Magnetospheres
通过三维磁流体模拟，研究恒星风条件如何影响阿尔文翼结构和磁层形态，发现上游阿尔文马赫数决定磁层构型，翼开角与恒星风速度相关，并揭示磁层顶与磁尾的线性标度关系。
Differentiating the acceleration mechanisms in the slow and Alfvénic slow solar wind
本研究利用Solar Orbiter与Parker Solar Probe的联合观测，对比慢太阳风与阿尔芬慢太阳风的能量学，发现阿尔芬慢太阳风需波压力梯度驱动，而非阿尔芬慢太阳风可由热压梯度驱动。
Understanding the mechanism(s) of the solar wind acceleration is important in astrophysics and geophysics. A promising model of the solar wind acceleration is known as the wave/turbulence-driven (WTD) model, in which Alfvén waves feed energy to the solar wind. In this study, we tested the WTD model with global measurement of wind speed from interplanetary scintillation (IPS) observations. For Carrington rotations in minimal and maximal activity phases, we selected field lines calculated by the potential-field source-surface method in high- and mid-latitudes and compared the simulated and obser…
The Effects of Non-Equilibrium Velocity Distributions on Alfvén Ion-Cyclotron Waves in the Solar Wind
本研究利用ALPS求解器对比太阳风质子实测VDFs与双麦克斯韦拟合VDFs的阿尔文模特性，发现VDF结构对波增长/阻尼率影响显著，解释了双麦克斯韦模型不稳定性阈值无法完全约束观测的问题。
The long-term evolution of large-amplitude Alfven waves propagating in the solar wind is investigated by performing two-dimensional MHD simulations within the expanding box model. The linear and nonlinear phases of the parametric decay instability are studied for both circularly polarized waves in parallel propagation and for arc-polarized waves in oblique propagation. The non-monochromatic case is also considered. In the oblique case, the direct excitation of daughter modes transverse to the local background field is found for the first time in an expanding environment, and this transverse ca…
Solar wind modeling with the Alfven Wave Solar atmosphere Model driven by HMI-based Near-Real-Time maps by the National Solar Observatory
本研究使用NSO-HMI近实时综合图驱动AWSoM模型，模拟了第24太阳活动周不同活动水平的三个卡灵顿自转，结果重现了低日冕EUV发射并匹配了1 au原位观测，量化了总无符号开放磁通量。
During Parker Solar Probe's first orbit, the solar wind plasma has been observed in situ closer than ever before, the perihelion on November 6th 2018 revealing a flow that is constantly permeated by large amplitude Alfvénic fluctuations. These include radial magnetic field reversals, or switchbacks, that seem to be a persistent feature of the young solar wind. The measurements also reveal a very strong, unexpected, azimuthal velocity component. In this work, we numerically model the solar corona during this first encounter, solving the MHD equations and accounting for Alfvén wave transport and…
Characterizing the Impact of Alfvén Wave Forcing in Interplanetary Space on the Distribution of near-Earth Solar Wind Speeds
本文利用近日动能通量观测和太阳风演化模型，论证了行星际空间中的阿尔文波强迫是产生近地最快非瞬态太阳风速度分布的主要加速机制，并表明太阳风阿尔文性可将近地观测统计映射至源区拓扑结构。
Validity of using Elsässer variables to study the interaction of compressible solar wind fluctuations with a coronal mass ejection
本研究在 CME 背景下，利用 2.5D MHD 模型评估了 Elsässer 形式体系在分离含密度涨落的太阳风 Alfvén 扰动时的有效性，发现密度扰动会导致变量及反射系数约 10% 的偏差。
Evolution of an Alfvén Wave-Driven Proton Beam in the Expanding Solar Wind
本文通过模拟研究了日风中由阿尔芬波非线性驱动的质子束演化，揭示了动能不稳定性在质子束漂移中的作用，并探讨了非线性阿尔芬波动力学与扩展效应的相互作用对日风动力学的影响。
Observed Fluctuation Enhancement and Departure from WKB Theory in Sub-Alfvénic Solar Wind
该研究利用帕克太阳探测器数据，分析太阳风流速跨越阿尔文波速临界区域的涨落振幅，发现其能量非单调递减且违背WKB波作用量守恒，支持临界区存在原位能量输入。
Conversion Layer Controls the Evolution of Magnetic Deflections Near the Alfven Surface
研究发现阿伦夫表面附近的转换层通过将磁能转化为粒子能，控制磁偏转的发展并可能驱动超阿伦夫日风中的磁翻转形成。
In the parts of the solar corona and solar wind that experience the fewest Coulomb collisions, the component proton, electron, and heavy ion populations are not in thermal equilibrium with one another. Observed differences in temperatures, outflow speeds, and velocity distribution anisotropies are useful constraints on proposed explanations for how the plasma is heated and accelerated. This paper presents new predictions of the rates of collisionless heating for each particle species, in which the energy input is assumed to come from magnetohydrodynamic (MHD) turbulence. We first created an em…
The characteristics of Alfvén waves propagating in a direction oblique to the ambient magnetic field in a stellar wind environment are discussed. A kinetic formulation for a magnetized dusty plasma is adopted considering Maxwellian distributions of electrons and ions, and immobile dust particles electrically charged by absorption of plasma particles and by photoionization. The dispersion relation is numerically solved and the results are compared with situations previously studied where dust particles were not charged by photoionization, which is an important process in a stellar wind of a rel…
Using a three-dimensional compressible magnetohydrodynamic (MHD) simulation, we have reproduced the fast solar wind in a direct and self-consistent manner, based on the wave/turbulence driven scenario. As a natural consequence of Alfvenic perturbations at its base, highly compressional and turbulent fluctuations are generated, leading to heating and acceleration of the solar wind. The analysis of power spectra and structure functions reveals that the turbulence is characterized by its imbalanced (in the sense of outward Alfvenic fluctuations) and anisotropic nature. The density fluctuation ori…
In situ observations of large amplitude Alfvén waves heating and accelerating the solar wind
本文利用帕克太阳探测器和太阳轨道器的原位数据，揭示大振幅阿尔芬波通过阻尼和机械功为内日球层快速太阳风的加热与加速提供能量。
Alfvén wave propagation, reflection and trapping in the solar wind
本文通过1.5维MHD模拟研究太阳风中阿尔文波在密度增强结构处的反射与俘获，发现最大反射发生在密度增强宽度与波长相当时的窄范围内，并用半解析模型揭示了波干涉效应的关键作用。
Using a kinetic description of a homogeneous magnetized dusty plasma with Maxwellian distribution of electrons and protons and dust particles charged by inelastic collisions and by photoionization, we analyse the dispersion relation considering the case where waves and radiation propagate exactly parallel to the ambient magnetic field. The investigation emphasizes the changes that the photoionization process brings to the propagation and damping of the waves in a stellar wind environment, since Alfvén waves are believed to play a significant role in the heating and acceleration processes that …
Using linear Vlasov theory of plasma waves and quasi-linear theory of resonant wave-particle interaction, the dispersion relations and the electromagnetic field fluctuations of fast and Alfven waves are studied for a low-beta multi-ion plasma in the inner corona. Their probable roles in heating and accelerating the solar wind via Landau and cyclotron resonances are quantified. We assume that (1) low-frequency Alfven and fast waves have the same spectral shape and the same amplitude of power spectral density; (2) these waves eventually reach ion cyclotron frequencies due to a turbulence cascade…
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