Properties of Magnetohydrodynamic Turbulence in the Solar Wind

Dobrowolny, M.; Mangeney, A.; Veltri, P.

doi:10.1007/978-94-009-9100-2_20

Cited by 48 publications

(51 citation statements)

References 5 publications

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“…First, the general scenario of cascade and homogeneous turbulence decay has been found (Hossain et al 1995;Biskamp 2003) to proceed in MHD in much the same way as in hydrodynamics (Taylor 1935;von Kármán & Howarth 1938). Accordingly, we view the baseline description for a solar wind fluctuation model as one of homogeneous turbulence (Tu et al 1984;Zhou & Matthaeus 1990), which for simplicity we treat using a phenomenological (or one-point) theory for the evolution of the ''energy-containing eddies,'' adapted to an MHD context ( Dobrowolny et al 1980;Grappin et al 1982;Hossain et al 1995). Second, a notable feature of the MHD cascade is the tendency to develop anisotropy relative to the large-scale magnetic field.…”

Section: Theoretical Modelmentioning

confidence: 99%

Turbulent Heating of the Solar Wind by Newborn Interstellar Pickup Protons

Smith

Isenberg

Matthaeus

et al. 2006

ApJ

149

157

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Spacecraft missions to the outer heliosphere have shown that the thermal protons that make up the solar wind are hotter than simple adiabatic expansion would predict. We examine a theory that describes this heating by using the time-varying 1 AU measurements as input and comparing the predictions with observations in the outer heliosphere. Inside 20 AU wind shear and shocks provide the dominant energy source to drive the turbulence. Outside 20 AU little remains to inject energy into the fluctuations except newborn interstellar pickup protons. The theory is built on a combination of two-dimensional magnetohydrodynamic turbulence concepts and the latest kinetic theory describing the scattering of newborn interstellar pickup protons. We find that application of the theory to the observations produces encouraging agreement at the same time that it illuminates latitudinal effects associated with solar minimum conditions. A remaining challenge is to close the gap of a factor of 2 between observed and predicted proton temperatures beyond 40 AU. For this, we suggest that further structural development of the theory is needed, rather than ad hoc adjustment of the model parameters, which are reasonably well constrained by theory, simulation, and observations.

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Section: Theoretical Modelmentioning

confidence: 99%

Turbulent Heating of the Solar Wind by Newborn Interstellar Pickup Protons

Smith

Isenberg

Matthaeus

et al. 2006

ApJ

149

157

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“…The magnetic turbulence in the solar wind is known to be anisotropic [ Dobrowolny et al , 1980; Bavassano et al , 1982; Matthaeus et al , 1995; Gray et al , 1996]. Several spectrum models have been proposed to account for the anisotropy [ Carbone et al , 1995; Bieber et al , 1996; Matthaeus et al , 1996; Zank et al , 1998; Bhattacharjee and Ng , 2001] but a comprehensive understanding is still lacking.…”

Section: Introductionmentioning

confidence: 99%

Magnetic flux tube evolution in solar wind anisotropic magnetic turbulence

2004

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The magnetic turbulence in the solar wind causes a magnetic field line transport that is reflected in the propagation in space of charged particles. Assuming a small localized source, the distribution in space of energetic particles is determined, in part, by the shape of the magnetic flux tube. The spatial evolution of a magnetic flux tube is studied here by means of a numerical realization of three‐dimensional magnetic turbulence that takes into account the anisotropy of the solar wind turbulence and is quantified by correlation lengths in the three spatial directions. Several diagnostics of flux tube evolution are shown, such as patterns of the flux tube cross sections and histograms representing possible energetic particle intensity profiles. We show that flux tube evolution can be assessed by the Kubo number R = (δB/B0)(lz/lx), where δB/B0 is the turbulence level and lz (lx) is the correlation length parallel (transversal) to the background magnetic field B0. We find that when lz/lx (i.e., R) is large, the flux tube evolves very quickly, forming very fine, diffusive structures. These diffusive structures would correspond to a nearly Gaussian envelope for the energetic particle time profile detected by a spacecraft. On the other hand, when lz/lx is small, the flux tube evolves slowly, executing large coherent transverse displacements, and thereby forms well resolved (i.e., detached) intermittent high particle fluxes in observed energetic particle profiles. Hence an accurate study of the morphology of impulsive energetic particle events, when compared with our simulation results, can give information on the microphysical evolution of flux tubes in the solar wind and on the turbulence anisotropy. A first comparison indicates that lx ≃ 3–10lz is appropriate for the solar wind. Our study also allows us to reconcile fast field line transport with the observation of sharp composition or energetic particle gradients in the solar wind, since lx ≫ lz implies considerable transverse elongation of the flux tube cross section, with the possibility of non‐Gaussian, superdiffusive transport regimes.

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“…In a recent critical analysis of the present observations of almost incompressible Alfv6nic fluctuations in the solar wind [Dobrowolny et al, 1980a], several noticeable properties of such fluctuations were pointed out. One of them, obtained by comparing observational results with the equations of incompressible magnetohydrodynamics, is that such fluctuations should be a mixture of modes with two different polarizations, namely, purely Alfv6nic modes and modes which are the incompressible limit of slow magnetosonic waves.…”

Section: Introductionmentioning

confidence: 81%

“…In general, by analogy with developed hydrodynamic turbulence, which is essentially not normal [Orszag, 1970], we would expect also in MHD turbulence triple correlations between fluctuating quantities to be different from zero. Going to the scheme of the calculations of Dobrowolny et al [1980a], one becomes easily convinced that in the presence of triple correlations, the scaling (9) between eigenvalues will no longer hold true but would be replaced by more complicated relations. Thus the fact that the testing of (9) with the experimental data, presented in this paper, has not given such high correlation coefficients as the testing of the single point relation (6) may also reflect the deviation from normality of the MHD turbulence in the solar wind.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

On the polarization state of hydromagnetic fluctuations in the solar wind

Bavassano¹,

Dobrowolny²,

Mariani³

et al. 1981

J. Geophys. Res.

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From presently available observations one can infer that the Alfv6nic turbulence measured in the solar wind, predominantly on trailing edges of high speed streams, is a mixture of modes with two different polarizations, namely, Alfv6nic modes and modes which are the incompressible limit of slow magnetosonic waves. Using Helios 2 magnetic data and a variance analysis, we have separated parallel (to the mean field) and perpendicular components of the fluctuations and studied the possible correlation between such components which would be predicted as a consequence of the incompressible character of the turbulence. Correlations between eigenvalues of the variance matrix are also investigated and discussed.

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Properties of Magnetohydrodynamic Turbulence in the Solar Wind

Cited by 48 publications

References 5 publications

Turbulent Heating of the Solar Wind by Newborn Interstellar Pickup Protons

Turbulent Heating of the Solar Wind by Newborn Interstellar Pickup Protons

Magnetic flux tube evolution in solar wind anisotropic magnetic turbulence

On the polarization state of hydromagnetic fluctuations in the solar wind

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