Evolving Solar Wind Flow Properties of Magnetic Inversions Observed by Helios

Macneil, Allan R, Owens, Mathew J, Wicks, Robert and Lockwood, Mike (2021) Evolving Solar Wind Flow Properties of Magnetic Inversions Observed by Helios. Monthly Notices of the Royal Astronomical Society, 501 (4). pp. 5379-5392. ISSN 0035-8711

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Official URL: https://doi.org/10.1093/mnras/staa3983

Abstract

In its first encounter at solar distances as close as r = 0.16AU, Parker Solar Probe (PSP) observed numerous local reversals, or inversions, in the heliospheric magnetic field (HMF), which were accompanied by large spikes in solar wind speed. Both solar and in situ mechanisms have been suggested to explain the existence of HMF inversions in general. Previous work using Helios 1, covering 0.3–1AU, observed inverted HMF to become more common with increasing r, suggesting that some heliospheric driving process creates or amplifies inversions. This study expands upon these findings, by analysing inversion-associated changes in plasma properties for the same large data set, facilitated by observations of ‘strahl’ electrons to identify the unperturbed magnetic polarity. We find that many inversions exhibit anti-correlated field and velocity perturbations, and are thus characteristically Alfvénic, but many also depart strongly from this relationship over an apparent continuum of properties. Inversions depart further from the ‘ideal’ Alfvénic case with increasing r, as more energy is partitioned in the field, rather than the plasma, component of the perturbation. This departure is greatest for inversions with larger density and magnetic field strength changes, and characteristic slow solar wind properties. We find no evidence that inversions which stray further from ‘ideal’ Alfvénicity have different generation processes from those which are more Alfvénic. Instead, different inversion properties could be imprinted based on transport or formation within different solar wind streams.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Elena Carlaw
Date Deposited: 12 Jan 2021 15:17
Last Modified: 04 Mar 2021 13:15
URI: http://nrl.northumbria.ac.uk/id/eprint/45202

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