On the Scaling Properties of Magnetic Field Fluctuations Through the Inner Heliosphere

TL;DR

This study analyzes magnetic field fluctuations in the solar wind using Parker Solar Probe data, revealing a transition from multifractal turbulence near the Sun to Kolmogorov turbulence farther away, indicating different turbulence regimes.

Contribution

It provides new insights into the multiscale turbulence properties of the solar wind at different heliocentric distances using high-resolution measurements.

Findings

Near the Sun, fluctuations follow a f^-3/2 spectrum with regular scaling.

Beyond 0.4 au, fluctuations exhibit a Kolmogorov f^-5/3 spectrum with anomalous scalings.

Turbulence transitions from multifractal to monofractal with increasing distance from the Sun.

Abstract

Although the interplanetary magnetic field variability has been extensively investigated in situ by means of data coming from several space missions, the newly launched missions providing high-resolution measures and approaching the Sun, offer the possibility to study the multiscale variability in the innermost solar system. Here by means of the Parker Solar Probe measurements we investigate the scaling properties of solar wind magnetic field fluctuations at different heliocentric distances. The results show a clear transition at distances close to say 0.4 au. Closer to the Sun fluctuations show a f^-3/2 frequency power spectra and regular scaling properties, while for distances larger than 0.4 au fluctuations show a Kolmogorov spectrum f^-5/3 and are characterized by anomalous scalings. The observed statistical properties of turbulence suggests that the solar wind magnetic fluctuations, in the late stage far form the Sun, show a multifractal behaviour typical of turbulence and described through intermittency, while in the early stage, when leaving the solar corona, a breakdown of these properties are observed, thus showing a statistical monofractal global self-similarity. Physically the breakdown observed close to the Sun should be due either to a turbulence with regular statistics or to the presence of intense stochastic fluctuations able to cancel out correlations necessary for the presence of anomalous scaling.