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

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, B2, 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 B2 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