Turbulence and intermittency in the heliospheric magnetic field in fast and slow solar wind

Abstract

We study the nonuniform solar wind turbulence using high‐resolution Ulysses magnetic field data measured at different solar activity level, heliospheric latitudes, and distance. We define several types of solar wind dependent of the coronal region of origin and also of the dynamical behavior of the different streams, namely, “pure” fast wind, fast streams, “pure” slow wind, and slow streams. The turbulent properties of the solar wind types were investigated in terms of their scaling properties and spatial inhomogeneity. A clear trend in the power spectrum of the solar wind magnetic field magnitude is observed: the “pure” fast wind has a slope ∼−1.33 (1/f‐like), the fast streams ∼−1.48 (Kraichnan‐like), the “pure” slow wind ∼−1.67 (Kolmogorov‐like), and the slow streams ∼−1.72. We find that the “pure” fast wind in the polar heliolatitudes is less intermittent than the other types: “pure” slow wind and both slow and fast streams, which is because of the absence of dynamical interactions between streams with different speeds. On the other hand, fast streams are more intermittent than the “pure” fast wind, and slow streams are less intermittent than the “pure” slow winds. A clear radial and latitudinal evolution of the intermittency is observed only for the “pure” fast wind, while in the equatorial plane, the fast streams, the “pure” slow wind, and the slow streams do not show evolution either in heliolatitude or in heliocentric distance.

The magnetohydrodynamic turbulent cascade in the ecliptic solar wind: Study of Ulysses data

“…5. This confirms that the energy transfer rate depends on the bulk velocity of the wind, in agreement with the observation of larger intermittency in the slow streams (Sorriso-Valvo et al, 1999;Yordanova et al, 2009). Moreover, in the fast streams only one of the modes (Y + or Y À ) is observed to satisfy the P&P law in a given location.…”

“…The properties of anisotropy and intermittency have been studied intensively (Osman and Horbury, 2009;Chen et al, 2010). Their dependence on parameters such as solar activity level, heliocentric distance, heliolatitude and wind speed has been pointed out (Bruno et al, 2003;Nicol et al, 2009;Yordanova et al, 2009). The stationarity of solar wind turbulence has been also questioned (Matthaeus and Goldstein, 1982), and is still discussed in the community.…”

Scaling law of the reduced magnetic helicity in fast streams

“…3 the partition function wðf Þ wð1=tÞ ¼ There is no plateau observed in the trends of the partition function around and above the ion-cyclotron frequency, thus implying that there is no predominance of a well-defined sign of polarization. Although the three events refer to pure fast wind streams (Yordanova et al, 2009) the cancellation exponents, coming from the power law best fits of the partition functions, are quite different. Indeed, the k 3 index in Fig.…”

Intermittency and regularity in the Alfvenic range of solar wind turbulence

“…The singularity spectrum has been extensively studied in neutral fluid and MHD turbulence as well as in solar wind turbulence (see for example the recent papers by Yordanova et al, [24], and Wawrzaszek and Macek, [25]); the reason is that turbulent flows are not spatially homogeneous: the irregularity of the velocity, magnetic fields, etc.. seems to differ widely from point to point. This phenomenon, called intermittency, manifests itself in a significant departure of the experimental data from the self-affine prediction based on the homogeneity assumption that, at each point of the fluid, the velocity and magnetic field increments have the same scaling behavior.…”