Solar wind vs magnetosheath turbulence and Alfvén vortices

Alexandrova, Olga

doi:10.5194/npg-15-95-2008

Cited by 108 publications

(115 citation statements)

References 70 publications

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“…Naturally, nonlinear structures responsible for turbulence have already been identified in planetary environments, in the solar wind, and also in the magnetosheath (e.g., Alexandrova, 2008). In particular, the magnetic fluctuations using Wind (Lion et al, 2016) and Cluster multi-spacecraft have been analyzed at ion scales (Yordanova et al, 2008;Figure 7.…”

Section: Magnetosheath Turbulencementioning

confidence: 99%

Intermittent turbulence in the heliosheath and the magnetosheath plasmas based on Voyager and THEMIS data

Macek

Wawrzaszek

Kucharuk

2018

Nonlin. Processes Geophys.

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Abstract. Turbulence is complex behavior that is ubiquitous in space, including the environments of the heliosphere and the magnetosphere. Our studies on solar wind turbulence including the heliosheath, and even at the heliospheric boundaries, also beyond the ecliptic plane, have shown that turbulence is intermittent in the entire heliosphere. As is known, turbulence in space plasmas often exhibits substantial deviations from normal Gaussian distributions. Therefore, we analyze the fluctuations of plasma and magnetic field parameters also in the magnetosheath behind the Earth's bow shock. Based on THEMIS observations, we have already suggested that turbulence behind the quasi-perpendicular shock is more intermittent with larger kurtosis than that behind the quasiparallel shocks. Following this study, we would like to present a detailed analysis of intermittent anisotropic turbulence in the magnetosheath depending on various characteristics of plasma behind the bow shock and now also near the magnetopause. In particular, for very high Alfvénic Mach numbers and high plasma beta we have clear non-Gaussian statistics in the directions perpendicular to the magnetic field. On the other hand, for directions parallel to this field the kurtosis is small and the plasma is close to equilibrium. However, the level of intermittency for the outgoing fluctuations seems to be similar to that for the ingoing fluctuations, which is consistent with approximate equipartition of energy between the oppositely propagating Alfvén waves. We hope that the difference in characteristic behavior of these fluctuations in various regions of space plasmas can help to detect some complex structures in space missions in the near future.

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Section: Magnetosheath Turbulencementioning

confidence: 99%

Intermittent turbulence in the heliosheath and the magnetosheath plasmas based on Voyager and THEMIS data

Macek

Wawrzaszek

Kucharuk

2018

Nonlin. Processes Geophys.

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“…Sahraoui et al (2010) interpret these observations as KAW turbulence, although Narita et al (2011) found no clear dispersion relation. 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).…”

Section: Turbulence Around Ion Scalesmentioning

confidence: 99%

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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“…The relation (25) obtained above allows the determination of the energy spectra E(k ⊥ ) of the strong vortex turbulence as a function of the to transversal "wave vector" k ⊥ similar to the work (Alexandrova, 2008). For this purpose let us use the formula of perturbation's energy (Eq.…”

Section: Turbulent Spectrummentioning

confidence: 99%

“…14). The energy density must be used in a compressible medium to describe the abovementioned cascade of energy, i.e., energy per unit volume (as it was made in the previous item) (Fleck, 1996;Kowal and Lazarian, 2007;Alexandrova, 2008), instead of the unit mass energy in order to take into account the medium fluctuations.…”

Section: Compressibilitymentioning

confidence: 99%

Model of strong stationary vortex turbulence in space plasmas

Aburjania

Chargazia

Zelenyǐ

et al. 2009

Nonlin. Processes Geophys.

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Abstract. This paper investigates the macroscopic consequences of nonlinear solitary vortex structures in magnetized space plasmas by developing theoretical model of plasma turbulence. Strongly localized vortex patterns contain trapped particles and, propagating in a medium, excite substantial density fluctuations and thus, intensify the energy, heat and mass transport processes, i.e., such vortices can form strong vortex turbulence. Turbulence is represented as an ensemble of strongly localized (and therefore weakly interacting) vortices. Vortices with various amplitudes are randomly distributed in space (due to collisions). For their description, a statistical approach is applied. It is supposed that a stationary turbulent state is formed by balancing competing effects: spontaneous development of vortices due to nonlinear twisting of the perturbations' fronts, cascading of perturbations into short scales (direct spectral cascade) and collisional or collisionless damping of the perturbations in the short-wave domain. In the inertial range, direct spectral cascade occurs through merging structures via collisions. It is shown that in the magneto-active plasmas, strong turbulence is generally anisotropic Turbulent modes mainly develop in the direction perpendicular to the local magnetic field. It is found that it is the compressibility of the local medium which primarily determines the character of the turbulent spectra: the strong vortex turbulence forms a power spectrum in wave number space. For example, a new spectrum of turbulent fluctuations in k −8/3 is derived which agrees with available experimental data. Within the framework of the developed model particle diffusion processes are also investigated. It is found that the interaction of structures with each other and particles causes anomalous diffusion in the medium. The effective coefficient of diffusion has a square root dependence on the stationary level of noise.

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Solar wind vs magnetosheath turbulence and Alfvén vortices

Cited by 108 publications

References 70 publications

Intermittent turbulence in the heliosheath and the magnetosheath plasmas based on Voyager and THEMIS data

Intermittent turbulence in the heliosheath and the magnetosheath plasmas based on Voyager and THEMIS data

Solar Wind Turbulence and the Role of Ion Instabilities

Model of strong stationary vortex turbulence in space plasmas

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