On the role of mirror mode instabilities in the reconnecting Heliospheric Current Sheet dynamics

Magnetic reconnection is a fundamental process in astrophysical plasma, as it enables the dissipation of energy at kinetic scales as well as large-scale reconfiguration of the magnetic topology. In the solar wind, its quantitative role in plasma dynamics and particle energization remains an open question that is starting to come into focus as more missions now probe the inner heliosphere. In particular, the first encounters of the Parker Solar Probe (PSP) mission with the Sun have revealed that the Heliospheric Current Sheet (HCS) was often reconnecting close to the Sun, opening question about the impact of HCS reconnection on the nearby solar wind.

In this work, we first make a thorough catalog of all HCS crossings measured PSP (encounter 5 to the latest available) and find that 88\% of crossings present magnetic reconnection signatures. This statistically confirms that magnetic reconnection is prevalent in the near Sun HCS. We then quantify the level of turbulence within the HCS and find enhanced energy at kinetic scales compared to the nearby solar wind, usually devoid of magnetic switchbacks. We furthermore highlight the frequent observation of mirror mode instabilities within the structure of the HCS, hinting that this process plays a particular role in the energy dissipation. These mirror mode instabilities are also observed within HCS crossings observed by Solar Orbiter further in the heliosphere. We finally plan to study the evolution of the HCS structure through multi-spacecraft observation.

Collectively, these results show that the HCS may play an important role in the energization of the near Sun solar wind. We discuss the impact of these observations on our current understanding of HCS reconnection and solar wind turbulence.