Evolving solar wind flow properties of magnetic inversions observed by Helios

Abstract

In its first encounter at solar distances as close as r = 0.16 au, Parker Solar Probe 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 0.3–1 au, 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 anticorrelated 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 that 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.

Reconstruction of Carrington Rotation means of Open Solar Flux over the past 154 years

“…Secondly there is what Lockwood, Owens, and Rouillard (2009b) termed "folded flux" and Owens, Crooker, and Lockwood (2013) termed "inverted flux" and which since the advent of Parker Probe observations is often called "switchbacks" (Bale et al, 2019;Jagarlamudi et al, 2023) in which the flux tube is bent back towards the Sun through of order 180 • . Before the Parker Solar Probe mission such structures were seen in data from several spacecraft, such as ISEE3 (Kahler, Crooker, and Gosling, 1996), Ulysses (Neugebauer et al, 1995;Balogh et al, 1999), ACE and Wind (Borovsky, 2016) and Helios (Horbury, Matteini, and Stansby, 2018;Macneil et al, 2020Macneil et al, , 2021. Using data from the Helios spacecraft, Macneil et al (2020) showed that switchbacks were absent in the innermost heliosphere and increased in occurrence with increasing heliocentric distance and so were generated in the heliosphere.…”

Could Switchbacks Originate in the Lower Solar Atmosphere? II. Propagation of Switchbacks in the Solar Corona

“…The distribution of detected deflection angles resembles a power-law without specific populations present (Dudok de Wit et al 2020). There is preliminary evidence that switchbacks become more common with increasing distance from the Sun (Macneil et al 2021). Nevertheless, the formation mechanism(s) of switchbacks, and whether they originate in the lower solar atmosphere or locally in the solar wind are intensively debated.…”