Velocity shear generation of solar wind turbulence

Roberts, D. A.; Goldstein, M. L.; Matthaeus, W. H.; Ghosh, S.

doi:10.1029/92ja01144

Cited by 189 publications

(147 citation statements)

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“…0148-0227/00/2000JA900004509.00 bulence evolution (e.g., see Roberts et al [1987Roberts et al [ , 1991Roberts et al [ , 1992 The results of our analysis for all the investigated intervals (no appreciable difference between northern and southern hemisphere is found) can be summarized as follows. For crc and Cvs a decrease for increasing distance is observed up to about 2 AU.…”

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confidence: 62%

Alfvénic turbulence in the polar wind: A statistical study on cross helicity and residual energy variations

Bavassano¹,

Pietropaolo²,

Bruno³

2000

J. Geophys. Res.

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Abstract.A study of MHD turbulence properties in the polar wind has been performed with Ulysses data. The parameters under examination are the normalized cross hellcity and the normalized residual energy. The correlation coefficient between velocity and magnetic field fluctuation vectors has also been computed. Both southern and northern phases of full immersion in the high-latitude fast wind have been examined. Observations during the short low-latitude phase around the Ulysses perihelion have been used as a term of comparison. Our results indicate that in the region up to about 2 AU the turbulence evolution leads to a decrease of cross helicity and Alfvanic correlation when distance increases. Farther out no appreciable va, riation is observed. It is concluded that in the high-la. titude hellosphere the MHD turbulence maintains a clea,r Alfvanic character even at large dista,nces. As regards the residual energy, a clea,r imba, la[nce in favor of the magnetic fluctuations is everywhere present. This imbalance becomes even more pronounced for increasing distance inside 2 AU, due to turbulence evolution. Other effects lead to an inversion of this trend in the outer region. It is noteworthy that the polar turbulence does not appear too different from that observed inside the trailing edge of low-latitude fast streams.

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confidence: 62%

Alfvénic turbulence in the polar wind: A statistical study on cross helicity and residual energy variations

Bavassano¹,

Pietropaolo²,

Bruno³

2000

J. Geophys. Res.

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“…On the converseside, in fast streams, where the magnetic field is more homogeneous, waves should travel almost undisturbed and the observed (although slower than in a slow wind) radial evolution of the Alfvénic turbulence need some mechanism to be ascribed to. Although it has been shown (Roberts et al, 1992;Goldstein et al, 1995) that plasma instabilities generated by velocity shears play a relevant role in the radial evolution of turbulence, another possibility is represented by parametric instability, as shown by Malara et al (2000) and Primavera et al (2003). These last studies related to parametric instability focus attention on the effects of this instability on the evolution of a large amplitude, circularly polarized, non-monochromatic Alfvén wave in a one-dimensional case.…”

Section: Results Of the Numerical Simulations Of Parametric Instabilitymentioning

confidence: 99%

On the probability distribution function of small-scale interplanetary magnetic field fluctuations

Bruno¹,

Carbone

Primavera

et al. 2004

Ann. Geophys.

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Abstract. In spite of a large number of papers dedicated to the study of MHD turbulence in the solar wind there are still some simple questions which have never been sufficiently addressed, such as: a) Do we really know how the magnetic field vector orientation fluctuates in space? b) What are the statistics followed by the orientation of the vector itself? c) Do the statistics change as the wind expands into the interplanetary space?A better understanding of these points can help us to better characterize the nature of interplanetary fluctuations and can provide useful hints to investigators who try to numerically simulate MHD turbulence.This work follows a recent paper presented by some of the authors which shows that these fluctuations might resemble a sort of random walk governed by Truncated Lévy Flight statistics. However, the limited statistics used in that paper did not allow for final conclusions but only speculative hypotheses. In this work we aim to address the same problem using more robust statistics which, on the one hand, forces us not to consider velocity fluctuations but, on the other hand, allows us to establish the nature of the governing statistics of magnetic fluctuations with more confidence.In addition, we show how features similar to those found in the present statistical analysis for the fast speed streams of solar wind are qualitatively recovered in numerical simulations of the parametric instability. This might offer an alternative viewpoint for interpreting the questions raised above.

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“…(1) would involve parallel spectral transfer at order b͞B 0 [35,37,38]. Sources of turbulent energy are represented by S. From 1 AU to about 10 AU we expect that the principle source of replenishment for small-scale turbulence is instability associated with stream shear [2,39] between regions of fast ϳ700 km͞s wind and slow ϳ300 km͞s wind. Equation (1) is expected to remain valid for weakly compressible MHD [21] when the turbulent Mach number, density fluctuations, and propagating compressive fluctuation are small.…”

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Turbulence, Spatial Transport, and Heating of the Solar Wind

et al. 1999

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A phenomenological theory describes radial evolution of plasma turbulence in the solar wind from 1 to 50 astronomical units. The theory includes a simple closure for local anisotropic magnetohydrodynamic turbulence, spatial transport, and driving by large-scale shear and pickup ions. Results compare well to plasma and magnetic field data from the Voyager 2 spacecraft, providing a basis for a concise, tractable description of turbulent energy transport in a variety of astrophysical plasmas. [S0031-9007(99) Low-frequency fluctuations in the solar wind plasma represent perhaps the most extensively studied type of magnetohydrodynamic (MHD) turbulence, having been observed by spacecraft instruments for more than thirty years [1][2][3]. The observed turbulence displays properties expected of both hydrodynamic and MHD theories, including distinctive spectra and correlations [3,4]. Solar wind turbulence is a crucial element in coupling the lower corona plasma and the earth's magnetosphere, and in the transport of energetic charged particles throughout the solar-terrestrial environment. It is also a prototype for understanding stellar and galactic winds and astrophysical plasma flows in general. There has been notable progress in understanding the cascade process [5][6][7][8][9][10][11][12] that accompanies solar wind turbulence. So far, however, no single quantitative model has explained how turbulent energy flows from the largest interacting structures to the smallest dissipative scales where it is deposited as heat. In this Letter we present such a theory, based upon the dynamics of large-scale "eddies," which, controlled by a single similarity scale, drives a cascade that supplies thermal energy to the fluid plasma. The theoretical results compare well with measurements by the Voyager 2 spacecraft at heliocentric radial distances r from 1 astronomical units (AU) to beyond 30 AU. This motivates the development of similar phenomenological turbulence theories for nonlinear MHD flows in a variety of astrophysical plasmas.From the Helios and Mariner missions reaching inside 0.3 AU, to the Voyager and Pioneer explorations beyond 50 AU, spacecraft instruments have returned magnetic field data and plasma data (proton temperature, velocity, and density) that reveal the organized large-scale structure of the heliospheric plasma, along with transient mesoscale features such as coronal mass ejections and an ubiquitous but nonuniform admixture of fluctuations. Substantial fluctuation energy resides in an inferred range of spatial scales between the ion inertial scale (ഠ10 6 cm at 1 AU) and the observed correlation scale l (ഠ6 3 10 11 cm at 1 AU). The radial dependence of fluctuations in the low latitude solar wind is illustrated using Voyager 2 data in Figs. 1-3, which portray magnetic field variance (energy density in the turbulent magnetic field), correlation length, and proton temperature, from 1 AU to beyond 30 AU. To simultaneously explain these three data sets is a significant challenge. The main objective of this Letter is...

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Velocity shear generation of solar wind turbulence

Cited by 189 publications

References 61 publications

Alfvénic turbulence in the polar wind: A statistical study on cross helicity and residual energy variations

Alfvénic turbulence in the polar wind: A statistical study on cross helicity and residual energy variations

On the probability distribution function of small-scale interplanetary magnetic field fluctuations

Turbulence, Spatial Transport, and Heating of the Solar Wind

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