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Magnetic Connectivity in the Corona as a Source of Structure in the Solar Wind.

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Title: Magnetic Connectivity in the Corona as a Source of Structure in the Solar Wind.
Authors: Burkholder, B. L.1 blburkholder@alaska.edu, Otto, A.1, Delamere, P. A.1, Borovsky, J. E.2
Source: Journal of Geophysical Research. Space Physics. Jan2019, Vol. 124 Issue 1, p32-49. 18p.
Subject Terms: Solar wind, Solar photosphere, Magnetic fields in the solar corona, Magnetic structure, Magnetohydrodynamics
Abstract: Five decades of satellite data confirm that the solar wind contains many boundaries separating flow with distinct magnetic and plasma properties. Some speculate the boundaries in the solar wind found at Earth originate at the solar surface and are carried along with the expanding solar wind as fossil structures to 1 AU. This begs the question, is it the physics and magnetic structure above the photosphere that creates well‐defined boundaries between different magnetic flux regions at 1 AU in the solar wind? Magnetic boundaries in the corona exist all the time as topological features of null points in the field. These topological magnetic boundaries seem to be likely locations for plasma boundaries. It can be expected that these boundaries are typical locations where field line‐integrated quantities, such as field‐aligned current, experience large and abrupt changes. We perform three‐dimensional resistive magnetohydrodynamic simulations of the solar corona driven by photospheric foot point motions. We find that large and abrupt changes occur for field line‐integrated quantities across a magnetic topological boundary and the cause for these changes is the discontinuous mapping for magnetic field lines and thus for Alfvén waves across these boundaries. It is also demonstrated via in situ properties that thin layers of field‐aligned and perpendicular currents are frequently located at or close to topological boundaries. Plain Language Summary: The solar wind travels from the Sun to the orbit of Earth (where we can measure it) in a day or more, and it brings with it the signature of processes which happen on the solar surface. The structure that we observe in the solar wind at Earth's orbit resembles a group of waving inflatable tube‐man arms flailing about each other. These structures are "magnetic flux tubes," and their boundaries separate regions in the solar wind where the magnetic field, plasma density, and flow can be drastically different. In order to discern the origin of these structures, we perform simulations of the plasma and magnetic field on the solar surface, where the material that forms the solar wind begins its journey out to the orbit of Earth. We find that very specific features in the magnetic field are responsible for creating boundary‐like structures and that the plasma either side of these boundaries can evolve independently. This paper shows boundary structure in the solar magnetic field and plasma; however, the connection of these structures to the solar wind structure is not yet clear. Future work will address this question. Key Points: Magnetic topological boundaries in the corona are likely locations for in situ plasma and magnetic field changesWhere field line connectivity diverges, magnetic perturbations from different source regions are propagated to the same vicinityField‐aligned current layers associated with open flux mapping to different foot points on the photosphere may define "flux tube" walls [ABSTRACT FROM AUTHOR]
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Abstract:Five decades of satellite data confirm that the solar wind contains many boundaries separating flow with distinct magnetic and plasma properties. Some speculate the boundaries in the solar wind found at Earth originate at the solar surface and are carried along with the expanding solar wind as fossil structures to 1 AU. This begs the question, is it the physics and magnetic structure above the photosphere that creates well‐defined boundaries between different magnetic flux regions at 1 AU in the solar wind? Magnetic boundaries in the corona exist all the time as topological features of null points in the field. These topological magnetic boundaries seem to be likely locations for plasma boundaries. It can be expected that these boundaries are typical locations where field line‐integrated quantities, such as field‐aligned current, experience large and abrupt changes. We perform three‐dimensional resistive magnetohydrodynamic simulations of the solar corona driven by photospheric foot point motions. We find that large and abrupt changes occur for field line‐integrated quantities across a magnetic topological boundary and the cause for these changes is the discontinuous mapping for magnetic field lines and thus for Alfvén waves across these boundaries. It is also demonstrated via in situ properties that thin layers of field‐aligned and perpendicular currents are frequently located at or close to topological boundaries. Plain Language Summary: The solar wind travels from the Sun to the orbit of Earth (where we can measure it) in a day or more, and it brings with it the signature of processes which happen on the solar surface. The structure that we observe in the solar wind at Earth's orbit resembles a group of waving inflatable tube‐man arms flailing about each other. These structures are "magnetic flux tubes," and their boundaries separate regions in the solar wind where the magnetic field, plasma density, and flow can be drastically different. In order to discern the origin of these structures, we perform simulations of the plasma and magnetic field on the solar surface, where the material that forms the solar wind begins its journey out to the orbit of Earth. We find that very specific features in the magnetic field are responsible for creating boundary‐like structures and that the plasma either side of these boundaries can evolve independently. This paper shows boundary structure in the solar magnetic field and plasma; however, the connection of these structures to the solar wind structure is not yet clear. Future work will address this question. Key Points: Magnetic topological boundaries in the corona are likely locations for in situ plasma and magnetic field changesWhere field line connectivity diverges, magnetic perturbations from different source regions are propagated to the same vicinityField‐aligned current layers associated with open flux mapping to different foot points on the photosphere may define "flux tube" walls [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2018JA026132