Statistical properties of MHD fluctuations associated with high-speed streams from Helios-2 observations

Bavassano, B.; Dobrowolny, M.; Fanfoni, G.; Mariani, F.; Ness, N. F.

doi:10.1007/bf00151617

Cited by 155 publications

(124 citation statements)

References 19 publications

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“…In fact, we have the possibility to analyse high and low velocity periods that are well known in literature. In particular, the time intervals, referring to fast wind, correspond to the same stream which is observed after two solar rotations (Bavassano et al, 1982). Moreover, Bruno et al (1985), studying the same intervals, have shown that Alfvénicity rapidly evolves with heliocentric distances, being larger at 0.3 AU than at 1 AU.…”

Section: Waiting-time Dependence On Heliocentric Distancementioning

confidence: 54%

On the scaling of waiting-time distributions of the negative IMF Bz component

et al. 2006

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Abstract. Statistics associated with the fluctuations in solar wind parameters show a remarkable dependence on the solar activity phase. In particular, we focus our attention on the waiting-time statistics governing the MHD fluctuations of the z-component of the interplanetary magnetic field, which are important within the framework of the Sun-Earth connections, and briefly discuss the preliminary results. Data from several spacecrafts, covering different phases of the solar cycle and different radial distances, are used. We found that propagating Alfvénic fluctuations and convected structures strongly influence the statistics which vary from quasiPoissonian to power law.

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Section: Waiting-time Dependence On Heliocentric Distancementioning

confidence: 54%

On the scaling of waiting-time distributions of the negative IMF Bz component

et al. 2006

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“…The upper panel of Fig. 6 shows the histogram of magnetic field and σ 2 xyz the standard deviation of the magnetic field intensity and the trace of the variance matrix of the components, respectively (Bavassano et al, 1982a;Bruno and Bavassano, 1991). Both panels clearly indicate that the two regions characterized by σ C ∼1 and σ R ∼0 and σ C ∼0 and σ R ∼−1, respectively, show the lowest magnetic compressive level.…”

Section: Discussionmentioning

confidence: 95%

Magnetically dominated structures as an important component of the solar wind turbulence

et al. 2007

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Abstract. This study focuses on the role that magnetically dominated fluctuations have within the solar wind MHD turbulence. It is well known that, as the wind expands, magnetic energy starts to dominate over kinetic energy but we lack of a statistical study apt to estimate the relevance of these fluctuations depending on wind speed, radial distance from the sun and heliographic latitude. Our results suggest that this kind of fluctuations can be interpreted as non-propagating structures, advected by the wind during its expansion. In particular, observations performed in the ecliptic revealed a clear radial dependence of these magnetic structures within fast wind, but not within slow wind. At short heliocentric distances (∼0.3 AU) the turbulent population is largely dominated by Alfvénic fluctuations characterized by high values of normalized cross-helicity and a remarkable level of energy equipartition. However, as the wind expands, a new-born population, characterized by lower values of Alfvénicity and a clear imbalance in favor of magnetic energy becomes visible and clearly distinguishable from the Alfvénic population largely characterized by an outward sense of propagation. We estimate that more than 20% of all the analyzed intervals of hourly scale within fast wind are characterized by normalized cross-helicity close to zero and magnetic energy largely dominating over kinetic energy. Most of these advected magnetic structures result to be non-compressive and might represent the crossing of the border between adjacent flux tubes forming, as suggested in literature, the advected background structure of the interplanetary magnetic field. On the other hand, their features are also well fitted by the Magnetic Field Directional Turnings paradigm as proposed in literature.

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“…Anisotropy of MHD fluctuations in the solar wind, due to the background magnetic field transported away from the sun by the plasma flow [15,16], has been investigated through the minimum variance analysis [17]. This method gives informations about the energy distribution among the different components of magnetic fluctuations.…”

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Persistence of small-scale anisotropy of magnetic turbulence as observed in the solar wind

et al. 2006

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Abstract. -The anisotropy of magnetophydrodynamic turbulence is investigated by using solar wind data from the Helios 2 spacecraft. We investigate the behaviour of the complete high-order moment tensors of magnetic field increments and we compare the usual longitudinal structure functions which have both isotropic and anisotropic contributions, to the fully anisotropic contribution. Scaling exponents have been extracted by an interpolation scaling function. Unlike the usual turbulence in fluid flows, small-scale magnetic fluctuations remain anisotropic. We discuss the radial dependence of both anisotropy and intermittency and their relationship.The idea that small scales were statistically isotropic to a high degree, in spite of the anisotropy of large scales, is at the heart of the concept of universality underlying scaling behaviour in turbulent fluid flow [1]. As experiments became increasingly sophisticated, evidence for the presence of anisotropy for both scalar fields [2] and velocity fields [3] has grown up. To what extent scaling laws extracted from experiments are approximated by the scaling laws obtained from (isotropic) cascade models [4], became an urgent issue. A workable benchmark is represented by the following conjecture [5,6]. Suppose that for a given statistical measurable quantity, scaling features can be splitted into an isotropic and an anisotropic part. We might ask to what extent the ratio between the anisotropic and the isotropic part vanishes as the scale goes down. Of course if we are able to define quantities for which the isotropic part is exactly zero, we can measure scaling laws related entirely to the anisotropic part. A formal analysis to reveal the isotropic and anisotropic contributions to structure functions can be performed by considering their SO(3) decomposition [7]. This is based in a foliation of various j-sectors of the linear space generated by the structure functions. For a recent review on anisotropy in turbulent flows see [8].c EDP Sciences

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Statistical properties of MHD fluctuations associated with high-speed streams from Helios-2 observations

Abstract: Eielios 2 magnetic data have been used to derive scveraa y a itivi.

Cited by 155 publications

References 19 publications

On the scaling of waiting-time distributions of the negative IMF <i>B<sub>z</sub></i> component

On the scaling of waiting-time distributions of the negative IMF <i>B<sub>z</sub></i> component

Magnetically dominated structures as an important component of the solar wind turbulence

Persistence of small-scale anisotropy of magnetic turbulence as observed in the solar wind

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Statistical properties of MHD fluctuations associated with high-speed streams from Helios-2 observations

Abstract: Eielios 2 magnetic data have been used to derive scveraa y a itivi.

Cited by 155 publications

References 19 publications

On the scaling of waiting-time distributions of the negative IMF &lt;i&gt;B&lt;sub&gt;z&lt;/sub&gt;&lt;/i&gt; component

On the scaling of waiting-time distributions of the negative IMF &lt;i&gt;B&lt;sub&gt;z&lt;/sub&gt;&lt;/i&gt; component

Magnetically dominated structures as an important component of the solar wind turbulence

Persistence of small-scale anisotropy of magnetic turbulence as observed in the solar wind

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Product

Resources

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On the scaling of waiting-time distributions of the negative IMF <i>B<sub>z</sub></i> component

On the scaling of waiting-time distributions of the negative IMF <i>B<sub>z</sub></i> component