Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh31a1661c&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH31A-1661
Other
2159 Plasma Waves And Turbulence, 2162 Solar Cycle Variations (7536), 3265 Stochastic Processes (3235, 4468, 4475, 7857), 4475 Scaling: Spatial And Temporal (1872, 3270, 4277), 7857 Stochastic Phenomena (3235, 3265, 4475)
Scientific paper
In- situ spacecraft observations of plasma parameters are at minute (or below) resolution for intervals spanning the solar cycle and provide a large number of samples for statistical studies. These observations reveal that the power spectrum of the components of magnetic field typically has two characteristic features, an inertial range of turbulence over several orders of magnitude with approximately Kolmogorov power law and at lower frequencies, an approximately '1/f' energy containing range believed to be of direct coronal origin. On the other hand, the (much lower energy density) magnetic field magnitude power spectrum typically shows a single scaling range that spans these timescales. This is consistent with the idea that the power seen in the components, but not necessarily the magnitude, of magnetic field is dominated by Alfvenic turbulence in the evolving solar wind. Here, we use quantitative statistical techniques to explore the idea that the solar wind exhibits fluctuations over a broad range of timescales characteristic of magnetohydrodynamic (MHD) turbulence evolving in the presence of structures of direct coronal origin. We find a strong correlation between the solar cycle variation in the scaling properties of magnetic energy density fluctuations and the magnetic complexity of the coronal magnetic fields. At solar maximum in the ecliptic, the magnetic energy density as seen by WIND and ACE shows a fractal signature, whereas at minimum it is multifractal. This is corroborated by ULLYSES polar observations at solar minimum in quiet, fast solar wind where again, multifractal scaling is found. High magnetic complexity in the corona then corresponds to fractal, rather than multifractal scaling in magnetic energy density seen at 1AU; remarkably, this fractal signature dominates the full dynamic range of observations, extending across timescales typically identified with both the '1/f' and 'inertial range'. Intervals when WIND and ACE simultaneously sample the solar wind also provide direct observations of the correlation lengthscale of these fluctuations; these show (i) distinct correlation lengthscales for magnetic field magnitude and components and (ii) the correlation lengthscale for magnetic field magnitude tracks the solar cycle whereas that of the components is insensitive to it. An important question which we will also address is then whether the observation of multifractal scaling per -se uniquely maps onto in- situ turbulence, or whether multifractal scaling, seen in the magnitude of magnetic field rather than components, is of direct coronal origin, with implications for our understanding of the heating of the solar wind.
Chapman Sandra C.
Hnat Bogdan
Kiyani K. H.
Nicol R. M.
Wicks R.
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