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- Yordanova, Emiliya, et al.
(författare)
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Turbulence and intermittency in the heliospheric magnetic field in fast and slow solar wind
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:8, s. A08101-
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Tidskriftsartikel (refereegranskat)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 similar to-1.33 (1/f-like), the fast streams similar to-1.48 (Kraichnan-like), the "pure'' slow wind similar to-1.67 (Kolmogorov-like), and the slow streams similar to-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.
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- Noullez, A., et al.
(författare)
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Global picture of self-similar and non-self-similar decay in Burgers turbulence
- 2005
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Ingår i: Physical Review E. - 1539-3755. ; 71:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper continues earlier investigations of the decay of Burgers turbulence in one dimension from Gaussian random initial conditions of the power-law spectral type E-0(k)similar to vertical bar k vertical bar(n). Depending on the power n, different characteristic regions are distinguished. The main focus of this paper is to delineate the regions in wave number k and time t in which self-similarity can (and cannot) be observed, taking into account small-k and large-k cutoffs. The evolution of the spectrum can be inferred using physical arguments describing the competition between the initial spectrum and the new frequencies generated by the dynamics. For large wave numbers, we always have a k(-2) region, associated with the shocks. When n is less than 1, the large-scale part of the spectrum is preserved in time and the global evolution is self-similar, so that scaling arguments perfectly predict the behavior in time of the energy and integral scale. If n is larger than 2, the spectrum tends for long times to a universal scaling form independent of the initial conditions, with universal behavior k(2) at small wave numbers. In the interval 2 < n the leading behavior is self-similar, independent of n and with universal behavior k(2) at small wave number. When 1 < n < 2, the spectrum has three scaling regions: first, a vertical bar k vertical bar(n) region at very small k's with a time-independent constant; second, a k(2) region at intermediate wave numbers; finally, the usual k(-2) region. In the remaining interval n <-3 the small-k cutoff dominates and n also plays no role. We find also (numerically) the subleading term similar to k(2) in the evolution of the spectrum in the interval -3 < n < 1. High-resolution numerical simulations have been performed confirming both scaling predictions and analytical asymptotic theory.
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