Flux ropes and dynamics of the heliospheric current sheet

TL;DR

This study combines in situ observations from Solar Orbiter and PSP with 3D MHD simulations to analyze flux ropes near the heliospheric current sheet, revealing their formation via pressure instabilities and reconnection.

Contribution

It provides the first combined observational and simulation-based analysis of flux ropes near the HCS, elucidating their formation mechanisms and 3D structure.

Findings

Flux ropes are prevalent near the HCS in both observations and simulations.

Flux ropes form at helmet streamer tips through pressure-driven instabilities and tearing reconnection.

The 3D structure of flux ropes relates to the network of quasi-separatrices.

Abstract

Context. Solar Orbiter and PSP jointly observed the solar wind for the first time in June 2020, capturing data from very different solar wind streams, calm and Alfv\'enic wind as well as many dynamic structures. Aims. The aim here is to understand the origin and characteristics of the highly dynamic solar wind observed by the two probes, in particular in the vicinity of the heliospheric current sheet (HCS). Methods. We analyse the plasma data obtained by PSP and Solar Orbiter in situ during the month of June 2020. We use the Alfv\'en-wave turbulence MHD solar wind model WindPredict-AW, and perform two 3D simulations based on ADAPT solar magnetograms for this period. Results. We show that the dynamic regions measured by both spacecraft are pervaded with flux ropes close to the HCS. These flux ropes are also present in the simulations, forming at the tip of helmet streamers, i.e. at the base of the heliospheric current sheet. The formation mechanism involves a pressure driven instability followed by a fast tearing reconnection process, consistent with the picture of R\'eville et al. (2020a). We further characterize the 3D spatial structure of helmet streamer born flux ropes, which seems, in the simulations, to be related to the network of quasi-separatrices.