Intermittent Scaling of the Solar Wind Data from Ulysses: Multifractal Analysis
Anna Wawrzaszek, Space Research Centre , PAS, Warsaw, Poland, Wieslaw Marian Macek, Space Research Centre, Polish Academy of Sciences, Bartycka 18 A, 00-716 Warsaw, Poland and Marius Echim, Belgian Institute for Space Aeronomy, Brussels, Belgium; Institute of Space Sciences, Bucharest, Romania
Contact First Author: Anna Wawrzaszek; sanna@cbk.waw.pl
English Abstract:
We study the evolution of intermittency in interplanetary magnetic fields with the heliocentric distance and latitude by using large amount of data from Ulysses spacecraft measured during two solar minima (1995-1997, 2007-2008) and solar maximum (1999-2001). In particular, we consider small-scale fluctuations of the magnetic field embedded in the “pure” slow and fast solar wind. To distinguish different types of solar wind we use the following parameters: radial velocity, proton density, proton temperature, the distribution of charge states of oxygen ions, and compressibility of magnetic field. We exclude from our analysis any solar wind transients (shocks, CME, magnetic clouds), thus our analysis is relevant for the “pristine” state of the wind, fast and slow. In the next step we consider the chosen intervals for fast and slow solar wind and perform multifractal analysis of components of the fluctuating magnetic field. More precisely, to quantify the degree of multifractality (intermittency) we determine about 500 multifractal spectra of the selected data sets (magnetic field components and intensity) and fit the observations with models of the intermittent turbulence.
The multifractal characteristics of the solar wind turbulence depend on the heliographic latitudes, heliocentric distance, and phase of the solar cycle. In general, we observe a somewhat smaller degree of multifractality at high latitudes during solar minimum for the fast solar wind, where turbulence evolves more slowly as compared with that at the ecliptic plane. Moreover, it seems that the multifractality exhibits a latitudinal dependence with some symmetry with respect to the ecliptic plane. The performed analysis provide a supporting evidence that the small-scale magnetic field fluctuations observed by Ulysses exhibit a multifractal behavior that is a persistent feature of fast and slow wind, at solar maximum and minimum.
Research supported by the European Community’s Seventh Framework Programme (FP7=2007 - 2013) under grant agreement no 313038=STORM.
