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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L15108, doi:10.1029/2007GL029531, 2007

On the fractal nature of the magnetic field energy density in the solar wind

B. Hnat

Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, UK


S. C. Chapman

Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, UK


K. Kiyani

Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, UK


G. Rowlands

Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, UK


N. W. Watkins

Natural Complexity Programme, British Antarctic Survey, Cambridge, UK


Abstract

The solar wind exhibits scaling typical of intermittent turbulence in the statistics of in situ fluctuations in both the magnetic and velocity fields. Intriguingly, quantities not directly accessed by theories of ideal, incompressible, MHD turbulence, such as magnetic energy density, B 2, nevertheless show evidence of simple fractal (self-affine) statistical scaling. We apply a novel statistical technique which is a sensitive discriminator of fractality to the B 2 timeseries from WIND and ACE. We show that robust fractal behaviour occurs at solar maximum and determine the scaling exponents. The probability density function (PDF) of fluctuations at solar maximum and minimum are distinct. Power law tails are seen at maximum, and the PDF is reminiscent of a Lévy flight.

Received 9 February 2007; accepted 26 June 2007; published 10 August 2007.

Keywords: fractal; solar wind; turbulence.

Index Terms: 2164 Interplanetary Physics: Solar wind plasma; 2162 Interplanetary Physics: Solar cycle variations (7536); 7863 Space Plasma Physics: Turbulence (4490); 4440 Nonlinear Geophysics: Fractals and multifractals.

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Citation: Hnat, B., S. C. Chapman, K. Kiyani, G. Rowlands, and N. W. Watkins (2007), On the fractal nature of the magnetic field energy density in the solar wind, Geophys. Res. Lett., 34, L15108, doi:10.1029/2007GL029531.