Evolution of the magnetic field rotation distributions in the inner heliosphere

Abstract

Context. The nature and evolution of the solar wind magnetic field rotations is studied in data from the Parker Solar Probe. Aims. We investigated the magnetic field deflections in the inner heliosphere below 0.5 au in a distance- and scale-dependent manner to shed some light on the mechanism behind their evolution. Methods. We used the magnetic field data from the FIELDS instrument suite to study the evolution of the magnetic field vector increment and rotation distributions that contain switchbacks. Results. We find that the rotation distributions evolve in a scale-dependent fashion. They have the same shape at small scales regardless of the radial distance, in contrast to larger scales, where the shape evolves with distance. The increments are shown to evolve towards a log-normal shape with increasing radial distance, even though the log-normal fit works quite well at all distances, especially at small scales. The rotation distributions are shown to evolve towards a previously developed rotation model moving away from the Sun. Conclusions. Our results suggest a scenario in which the evolution of the rotation distributions is primarily the result of the expansion-driven growth of the fluctuations, which are reshaped into a log-normal distribution by the solar wind turbulence.