Variability of the slow solar wind: New insights from modelling and PSP-WISPR observations

TL;DR

This study combines advanced modelling and WISPR observations to analyze transient structures in the slow solar wind, revealing tearing-induced magnetic reconnection as a key driver of its variability.

Contribution

It introduces a new forward modelling algorithm and provides evidence linking magnetic reconnection to the variability of the slow solar wind.

Findings

Transient structures are formed by tearing-induced magnetic reconnection.

Simulated periodicities match observed timescales of 90-180min, 7-10hr, and 25-50hr.

Magnetic reconnection significantly contributes to slow solar wind variability.

Abstract

We analyse the signature and origin of transient structures embedded in the slow solar wind, and observed by the Wide-Field Imager for Parker Solar Probe (WISPR) during its first ten passages close to the Sun. WISPR provides a new in-depth vision on these structures, which have long been speculated to be a remnant of the pinch-off magnetic reconnection occurring at the tip of helmet streamers. We pursued the previous modelling works of Reville (2020b, 2022) that simulate the dynamic release of quasi-periodic density structures into the slow wind through a tearing-induced magnetic reconnection at the tip of helmet streamers. Synthetic WISPR white-light (WL) images are produced using a newly developed advanced forward modelling algorithm that includes an adaptive grid refinement to resolve the smallest transient structures in the simulations. We analysed the aspect and properties of the simulated WL signatures in several case studies that are typical of solar minimum and near-maximum configurations. Quasi-periodic density structures associated with small-scale magnetic flux ropes are formed by tearing-induced magnetic reconnection at the heliospheric current sheet and within 3-7Rs. Their appearance in WL images is greatly affected by the shape of the streamer belt and the presence of pseudo-streamers. The simulations show periodicities on ~90-180min, ~7-10hr and ~25-50hr timescales, which are compatible with WISPR and past observations. This work shows strong evidence for a tearing-induced magnetic reconnection contributing to the long-observed high variability of the slow solar wind.