Influence of the heliospheric current sheet on the evolution of solar wind turbulence

TL;DR

This study investigates how the heliospheric current sheet influences solar wind turbulence, revealing decreased Alfvénicity near the HCS and increased magnetic energy, supported by both simulations and observational data.

Contribution

It combines MHD simulations with observational analysis to show the impact of the HCS on turbulence properties in the solar wind, highlighting the weakening of Alfvénic features.

Findings

Alfvénicity decreases near the HCS

Magnetic energy excess is observed at the HCS center

Simulation results align with OMNI data analysis

Abstract

The effects of the heliospheric current sheet (HCS) on the evolution of Alfv\'enic turbulence in the solar wind are studied using MHD simulations incorporating the expanding-box-model (EBM). The simulations show that near the HCS, the Alfv\'enicity of the turbulence decreases as manifested by lower normalized cross helicity and larger excess of magnetic energy. The numerical results are supported by a superposed-epoch analysis using OMNI data, which shows that the normalized cross helicity decreases inside the plasma sheet surrounding HCS, and the excess of magnetic energy is significantly enhanced at the center of HCS. Our simulation results indicate that the decrease of Alfv\'enicity around the HCS is due to the weakening of radial magnetic field and the effects of the transverse gradient in the background magnetic field. The magnetic energy excess in the turbulence may be a result of the loss of Alfv\'enic correlation between velocity and magnetic field and the faster decay of transverse kinetic energy with respect to magnetic energy in a spherically expanding solar wind.