Identification of periodic density structures in Solar Orbiter data: Radial evolution

TL;DR

This study analyzes quasi-periodic density structures in solar wind data from Solar Orbiter, revealing their radial evolution and suggesting they form near the Sun through magnetic reconnection processes.

Contribution

It provides the first extensive statistical analysis of PDS radial scales at various distances from the Sun using Solar Orbiter data.

Findings

PDS expand by about 10% in slow solar wind

PDS compress by about 10% in fast solar wind

PDS likely originate from magnetic reconnection in the solar corona

Abstract

The quasi-Periodic density structures (PDSs) are quasiperiodic variations of solar wind density ranging from a few minutes to a few hours. They are trains of advected density structures with radial length scales LR in the 100-10,000 Mm range, thus belonging to the class of solar wind mesoscale structures. Even though PDS at L1 have been extensively studied both through statistical and event analysis, their investigation at distances closer to the Sun is limited. This study performs a statistical investigation of PDS at various distances from the Sun between 0.3 and 1 AU by exploiting Solar Orbiter data. We compiled and made publicly available an extensive list of PDSs following a well-established methodology that combines the Multitaper method as well as wavelet analysis to reveal the distribution of PDS radial length scales and how they vary with respect to the radial distance. Our results indicate that PDS advected with the ambient slow solar wind are expanded at a rate of approximately 10%, while PDS detected during fast solar wind segments show compression at a similar rate. These are consistent with the scenario in which PDSs are formed at the Sun by processes involving magnetic reconnection and interchange reconnection in the solar corona.