The near-Sun Heliospheric Current Sheet, fluid and kinetic properties

TL;DR

This study uses Parker Solar Probe data to analyze the near-Sun heliospheric current sheet, revealing frequent magnetic reconnection, turbulence enhancement, and the role of mirror mode instability in high beta plasma environments.

Contribution

First statistical analysis of HCS properties close to the Sun using PSP data, highlighting reconnection, turbulence, and kinetic instabilities in the high beta plasma environment.

Findings

82% of HCS crossings show reconnection signatures

Turbulence is enhanced in the ion kinetic range near the HCS

Magnetic hole trains and mirror mode instability regulate ion temperature anisotropy

Abstract

The heliospheric current sheet (HCS) is an important large-scale structure of the heliosphere, and, for the first time, the Parker Solar Probe (PSP) mission enables us to study its properties statistically close to the Sun. We visually identify the 39 HCS crossings measured by PSP below 50~\Rs~during encounters 6 to 21, and investigate the occurrence and properties of magnetic reconnection, the behavior of the spectral properties of the turbulent energy cascade, and the occurrence of kinetic instabilities at the HCS. We find that 82\% of HCS crossings present signatures of reconnection jets, showing that the HCS is continuously reconnecting close to the Sun. The proportion of inward/outward jets depends on heliocentric distance, and the main HCS reconnection X-line has a higher probability of being located close to the Alfv\'en surface. We also observe a radial asymmetry in jet acceleration, where inward jets do not reach the local Alfv\'en speed, contrary to outward jets. We find that turbulence levels are enhanced in the ion kinetic range, consistent with the triggering of an inverse cascade by magnetic reconnection. Finally, we highlight the ubiquity of magnetic hole trains in the high $\beta$ environment of the HCS, showing that the mirror mode instability plays a key role in regulating the ion temperature anisotropy in HCS reconnection. Our findings shed new light on the properties of magnetic reconnection in the high $\beta$ plasma environment of the HCS, its interplay with the turbulent cascade and the role of the mirror mode instability.