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The effect of thermal nonequilibrium on helmet streamer plasma and the solar wind
Dissertation   Open access

The effect of thermal nonequilibrium on helmet streamer plasma and the solar wind

Michael John Schlenker
Doctor of Philosophy (Ph.D.), Drexel University
Sep 2018
DOI:
https://doi.org/10.17918/D8K38R
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Abstract

Nonequilibrium thermodynamics Solar wind Physics
Helmet streamers are comprised of long magnetic loops that define the boundary between open and closed magnetic flux on the Sun. Since observations from Sheeley et al. (1997), these features have been shown to release plasmoids from their cusp into the slow solar wind. Further observations of these transient features in Viall & Vourlidas (2015) revealed that these plasmoids contained substructures in their densities with periodicities of approximately 90 minutes. Previous efforts to model helmet streamers (Endeve et al. (2003), Allred & MacNeice (2008)) were unsuccessful in producing density variations on such timescales. Here, we propose and investigate with numerical simulations the process of thermal nonequilibrium (TNE) as the mechanism that produces the slow wind substructure. TNE is a process where coronal material can rapidly cool to chromospheric temperatures provided that the length of magnetic loops is a factor of 8 larger than the heating scale height of the corona (Antiochos et al. (1999); Karpen et al. (2001a)). We utilize a 2.5 MHD code called Arc7 (Allred & MacNeice (2008)) to demonstrate that helmet streamers can undergo the TNE process and calculate the effects of this process on the evolution of the streamer's magnetic field. We then proceed to analyze the character of the solar wind plasma above the streamer in cases where TNE is and is not present within the system. A comparison of these two cases shows that a streamer experiencing TNE will exhibit more density structure at higher periodicities than that seen for a streamer not undergoing TNE. Density variations ranged from 15 to over 20 hours if TNE was not present within the helmet streamer to approximately 5 hours if TNE was shown to occur. Furthermore, the solar wind density profile in the cases with TNE showed substructures that are very similar to those seen in the observations. This proof of concept recommends further study in this area to ascertain whether time scales down to 90 minutes can be achieved. These results also establish that a deep connection between coronal heating and solar wind dynamics exists.

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