Towards Data-Driven Modelling of Magnetic Switchbacks Observed by the Parker Solar Probe Mission

Kumar, Anmol (2022) Towards Data-Driven Modelling of Magnetic Switchbacks Observed by the Parker Solar Probe Mission. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Anmol Kumar (17MS028)) 17MS028_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (6MB)

Abstract

Our current understanding of the solar wind is based on Parker’s model proposed in 1958. However, there are still certain gaps in our understanding, especially the solar wind acceleration process and the presence of transients, small-scale structures in the wind. In order to resolve these conundrums, NASA launched the Parker Solar Probe (PSP) in 2018 with the aim of studying plasma conditions close to the solar corona where solar wind acceleration occurs. Parker’s solar wind model predicts a spiral structure of magnetic field in the heliosphere owing to the Sun’s rotation. However, recent observations by the PSP has revealed the presence of short-term reversals in magnetic field, propagating out with the solar wind. These magnetic field structures are called switchbacks. Since switchbacks are regions of complex magnetic field configurations, they may host events such as magnetic reconnection that might be linked to the acceleration of the solar wind in the inner heliosphere. Therefore, it becomes imperative to understand their origin, their evolution as well as interactions with the solar wind background. This thesis aims to answer such questions, first, via direct observations, and then via numerical modelling of switchbacks. Our study consists of a detailed statistical analysis of PSP FIELDS and SWEAP instrument suites that measure in situ plasma parameters. The dataset consists of the first nine solar encounters of the PSP, with more than 2000 switchback events detected in total, and a spatial extent ranging from heliocentric distances as low as 0.07 AU to as high as 0.32 AU. A distance based statistical analysis of different physical parameters inside switchbacks reveal remarkable features about their evolution and interactions with the background solar wind through the inner heliosphere. We report that switchbacks are initially plasma dominated that get advected with the solar wind, preserving their structures via the action of magnetic tension forces. As the wind dominance reduces, switchbacks tend to die out, transferring momentum and energy, both kinetic and thermal, to the background solar wind, thus possibly contributing to solar wind acceleration. Therefore, we predict the existence of a region in the heliosphere where switchbacks would have decayed and merged with the background leading to lack of switchback observations in the near-Earth environment at 1 AU. Based upon these findings, we perform two-dimensional kinematic simulations to mimic the formation and decay of switchbacks originating from a persistent rotational flow of the solar wind plasma. A detailed parameter space study establishes a positive correlation between the switchback formation time and lifetime.

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