The interaction between the solar wind and the partially ionized gas of the local interstellar medium (ISM) creates a bubble known as the heliosphere. Classically, the shape of the heliosphere has been regarded as comet-like, with a long tail pointed in the direction opposite the Sun’s motion through the ISM. In this view, the solar magnetic field was assumed to have a negligible effect on the global structure of the heliosphere. Recent advances in numerical modeling have revealed the importance of the solar magnetic field in its ability to confine and collimate the solar wind plasma, and the shape of the heliosphere has been called into question. Energetic neutral atoms (ENAs) are created throughout the heliosphere via charge exchange. The separate contributions of the solar magnetic field topology and the solar wind structure to ENA observations is largely unexplored. The Interstellar Boundary Explorer (IBEX) has been providing a global perspective of the heliosphere through ENA maps with energies ranging from 0.2 to 6 keV.
In this dissertation, three-dimensional magnetohydrodynamic simulations of the heliosphere are used as input to an ENA model designed to produce synthetic ENA maps. I compare modeled ENA maps with IBEX observations to investigate how different heliospheric conditions and properties affect ENAs created in the heliosphere, and therefore how ENA observations can be used to understand the heliosphere. First, I investigate the effect of the solar wind collimation by the solar magnetic field on ENA maps in the case of a solar wind without latitudinal variation. I find that even in the absence of variations of the solar wind, two lobes of strong ENA flux form at high latitudes, similar to what is observed by IBEX at high energies. Second, I test the effect of a latitudinally-varying solar wind on ENAs both with and without the inclusion of the solar magnetic field. I show that the latitudinal variations of the solar wind during solar minimum creates a structured ENA profile with latitude, corresponding to the profile observed at 1 AU, but that the solar magnetic field significantly enhances ENA flux in the region where the solar wind is confined. Lastly, I investigate the effect of the solar cycle on ENAs and how changing solar wind conditions (e.g. density, temperature, velocity) affect the heliosphere over time. I demonstrate that, given changes in the solar cycle, there is a significant evolution in the modeled ENA flux due to the changes in the solar wind profile and the solar magnetic field, which is also seen by ENA observations.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/42001 |
| Date | 07 February 2021 |
| Creators | Kornbleuth, Marc Zachary |
| Contributors | Opher, Merav |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NonCommercial-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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