Possible Evidence of Alfvén-Cyclotron Waves in the Angle Distribution of Magnetic Helicity of Solar Wind Turbulence

He, Jiansen; Marsch, E.; Tu, Chuanyi; Yao, Shuo; Tian, Hui

doi:10.1088/0004-637x/731/2/85

Cited by 205 publications

(238 citation statements)

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“…Some theoretical results and solar wind observations suggest that ion cyclotron waveparticle interactions are an important source of heating for solar wind ions (Marsch and Tu 2001;Isenberg et al 2001;Kasper et al 2008Kasper et al , 2013Bourouaine et al 2010He et al 2011b). However, this interpretation requires substantial turbulent energy at k ρ i ≈ 1, that is in apparent contradiction to the Goldreich-Sridhar model and to the solar wind measurements described in the following section (Horbury et al 2008;Podesta 2009;Luo and Wu 2010;Wicks et al 2010;2011;Chen et al 2011a).…”

Section: The Mhd Scale Cascadementioning

confidence: 99%

“…Magnetic fluctuations with nearly zero frequency and k ⊥ k can also be due to non-propagative coherent structures like current sheets (Veltri et al 2005;Greco et al 2010;Perri et al 2012), shocks (Salem 2000;Veltri et al 2005;Mangeney et al 2001), current filaments (Rezeau et al 1993), or Alfvén vortices propagating with a very slow phase speed ∼ 0.1V A in the plasma frame (Petviashvili and Pokhotelov 1992;Alexandrova 2008). Such vortices are known to be present within the ion transition range (He et al 2011b) of the planetary magnetosheath turbulence, when ion beta is relatively low β i ≤ 1 (Alexandrova et al 2006;Alexandrova and Saur 2008). Recent Cluster observations in the fast solar wind suggest that the ion transition range can be populated with KAWs and Alfvén vortices (Roberts et al 2013).…”

Section: Turbulence Around Ion Scalesmentioning

confidence: 99%

“…Magnetic helicity is defined as A · B , where B = ∇ × A, with A being the vector potential. It has been measured that at ion scales the magnetic helicity is anisotropic (He et al 2011b). Figure 11 shows the reduced magnetic helicity 14 σ m as a function of the time scale and of the local flow-to-field angle θ BV .…”

Section: Turbulence Around Ion Scalesmentioning

confidence: 99%

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Solar Wind Turbulence and the Role of Ion Instabilities

et al. 2013

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Solar wind is probably the best laboratory to study turbulence in astrophysical plasmas. In addition to the presence of magnetic field, the differences with neutral fluid isotropic turbulence are: (i) weakness of collisional dissipation and (ii) presence of several characteristic space and time scales. In this paper we discuss observational properties of solar wind turbulence in a large range from the MHD to the electron scales. At MHD scales, within the inertial range, turbulence cascade of magnetic fluctuations develops mostly in the plane perpendicular to the mean field, with the Kolmogorov scaling k −5/3 ⊥ for the perpendicular cascade and k −2 for the parallel one. Solar wind turbulence is compressible in nature: density fluctuations at MHD scales have the Kolmogorov spectrum. Velocity fluctuations do not follow magnetic field ones: their spectrum is a power-law with a −3/2 spectral index. Probability distribution functions of different plasma parameters are not Gaussian, indicating presence of intermittency. At the moment there is no global model taking into account all these observed properties of the inertial range. At ion scales, turbulent spectra have a break, compressibility increases and the density fluctuation spectrum has a local flattening. Around ion scales, magnetic spectra are variable and ion instabilities occur as a function of the local plasma parameters. Between ion and electron scales, a small scale turbulent cascade seems to be established. It is characterized by a well defined power-law spectrum in magnetic and density fluctuations with a spectral index close to −2.8. Approaching electron scales, the fluctuations are no more self-similar: an exponential cut-off is usually observed (for time intervals without quasi-parallel whistlers) indicating an onset of dissipation. The small scale inertial range between ion and electron scales and the electron dissipation range can be together described by ∼ k −α ⊥ exp(−k ⊥ d ), with α 8/3 and the dissipation scale d close to the electron Larmor radius d ρ e . The nature of this small scale cascade and a possible dissipation mechanism are still under debate.

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Section: The Mhd Scale Cascadementioning

confidence: 99%

Section: Turbulence Around Ion Scalesmentioning

confidence: 99%

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Solar Wind Turbulence and the Role of Ion Instabilities

et al. 2013

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“…Our motivation for this focus is threefold. First, there may be a sufficient level of power in Alfvénic fluctuations in the solar wind to sustain this mode of heating [23,24]. Second, ion-cyclotron resonance could explain the large temperature anisotropies [2,8,25] and growing magnetic moments seen with distance from the Sun [26].…”

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confidence: 99%

Sensitive Test for Ion-Cyclotron Resonant Heating in the Solar Wind

et al. 2013

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Plasma carrying a spectrum of counter-propagating field-aligned ion-cyclotron waves can strongly and preferentially heat ions through a stochastic Fermi mechanism. Such a process has been proposed to explain the extreme temperatures, temperature anisotropies, and speeds of ions in the solar corona and solar wind. We quantify how differential flow between ion species results in a Doppler shift in the wave spectrum that can prevent this strong heating. Two critical values of differential flow are derived for strong heating of the core and tail of a given ion distribution function. Our comparison of these predictions to observations from the Wind spacecraft reveals excellent agreement. Solar wind helium that meets the condition for strong core heating is nearly seven times hotter than hydrogen on average. Ion-cyclotron resonance contributes to heating in the solar wind, and there is a close link between heating, differential flow, and temperature anisotropy. Introduction.-The solar corona and solar wind are so tenuous that wave-particle interactions can dominate over fluid or collisional processes, resulting in highly nonthermal plasma as seen by spacecraft in interplanetary space. Heavier ions escape from the Sun at higher speeds than the ionized hydrogen (H + ) that dominates the solar wind. Within a given solar wind stream, different species flow through one another at speeds of up to several hundred km s −1 [1,2]. This differential flow appears to be stable as long as it is aligned with the local magnetic field B and below the Alfvén wave speed C A [3,4]. Heavier ions are also often much hotter than H + , with temperatures reaching and often exceeding mass proportionality [5][6][7][8]. These non-thermal properties can be used to identify the role wave-particle interactions play in heating the corona and solar wind [9][10][11]. If we can understand the underlying physics, we will be able to predict the relative heating of ions and electrons in the solar wind, the corona and other magnetized plasmas.

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“…Multispacecraft measurement of solar wind magnetic field fluctuations at the ion gyro-radius or inertial scales often show that the dominant power of fluctuations is in directions of almost perpendicular (to the background magnetic field) propagation (Sahraoui et al 2010;Narita et al 2011;Roberts et al 2013). A less powerful parallel propagating component may also exist (He et al 2011;Podesta and Gary 2011). The data used for these studies are obtained at 1 AU or beyond, not in regions that the results of this paper can directly apply to (3 solar radii to 0.3 AU).…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Ion Dynamics During the Parametric Instabilities of a Left-Hand Polarized Alfvén Wave in a Proton-Electron-Alpha Plasma

Gao

et al. 2013

ApJ

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The parametric instabilities of an Alfvén wave in a proton-electron plasma system are found to have great influence on proton dynamics, where part of the protons can be accelerated through the Landau resonance with the excited ion acoustic waves, and a beam component along the background magnetic field is formed. In this paper, with a onedimensional hybrid simulation model, we investigate the evolution of the parametric instabilities of a monochromatic left-hand polarized Alfvén wave in a proton-electron-alpha plasma with a low beta. When the drift velocity between the protons and alpha particles is sufficiently large, the wave numbers of the backward daughter Alfvén waves can be cascaded toward higher values due to the modulational instability during the nonlinear evolution of the parametric instabilities, and the alpha particles are resonantly heated in both the parallel and perpendicular direction by the backward waves. On the other hand, when the drift velocity of alpha particles is small, the alpha particles are heated in the linear growth stage of the parametric instabilities due to the Landau resonance with the excited ion acoustic waves. Therefore, the heating occurs only in the parallel direction, and there is no obvious heating in the perpendicular direction. The relevance of our results to the preferential heating of heavy ions observed in the solar wind within 0.3 AU is also discussed in this paper.

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Possible Evidence of Alfvén-Cyclotron Waves in the Angle Distribution of Magnetic Helicity of Solar Wind Turbulence

Cited by 205 publications

References 33 publications

Solar Wind Turbulence and the Role of Ion Instabilities

Solar Wind Turbulence and the Role of Ion Instabilities

Sensitive Test for Ion-Cyclotron Resonant Heating in the Solar Wind

Ion Dynamics During the Parametric Instabilities of a Left-Hand Polarized Alfvén Wave in a Proton-Electron-Alpha Plasma

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