We briefly review an existing model of the structure of reconnection layers which predicts that several more distinct layers, in the form of contact discontinuities, rotational Alfvèn waves, or slow shocks, should be identifiable in solar wind reconnection events than are typically reported in studies of reconnection outflows associated with bifurcated current sheets. We re-examine this notion and recast the identification of such layers in terms of the changes associated with the boundaries of both the ion and electron outflows from the reconnection current layers. We then present a case study using Solar Orbiter MAG and SWA data, which provides evidence consistent with this picture of extended multiple layers around the bifurcated current sheet. A full confirmation of this picture requires more detailed examination of the particle distributions in this and other events. However, we believe this concept is a valuable framework for considering the nature of reconnection layers in the solar wind.
<p><em>Context</em>: Magnetic switchbacks are localised polarity reversals in the radial component of the heliospheric magnetic field. Observations from <em>Parker Solar Probe </em>(PSP) have shown that they are a prevalent feature of the near-Sun solar wind. However, observations of switchbacks at 1 au and beyond are less frequent, suggesting that these structures are dissipated by yet-to-be identified mechanisms as they propagate away from the Sun.</p> <p><em>Aims</em>: We estimate the timescales over which magnetic switchbacks may be dissipated by magnetic reconnection and evaluate the viability of reconnection as a dissipation mechanism for switchbacks.</p> <p><em>Methods</em>: We analyse magnetic field and plasma data from the magnetometer and Solar Wind Analyser instruments aboard <em>Solar Orbiter</em> between 10 August and 30 August 2021. During this period, the spacecraft was 0.6 &#8211; 0.7 au from the Sun.</p> <p><em>Results</em>: We identify three instances of reconnection occurring at the trailing edge of magnetic switchbacks. Using hodographs and Walen analysis methods, we find that the reconnection exhaust region for all three events are bound by rotational discontinuities in the magnetic field, consistent with existing models describing the properties of reconnection in the solar wind. Based on these observations, we propose a scenario through which reconnection can dissipate a switchback and we estimate the timescales over which this occurs. We find that for our events the dissipation timescales are much shorter than the expansion timescale and thus, the complete dissipation of all three observed switchbacks would occur well before they reach Earth. Furthermore, assuming the observed reconnection rate has remained constant, and extrapolating back to an origin close to the Sun, we find that the spatial scale of these switchbacks would be considerably larger than is typically seen in the inner heliosphere. Hence, it is implied that the onset of reconnection must occur during transport in the solar wind. If typical, these results suggest that reconnection can play a significant role in dissipating switchbacks and could help explain the relative rarity of switchback observations at 1 au.</p>
Context. Magnetic switchbacks are localised polarity reversals in the radial component of the heliospheric magnetic field. Observations from Parker Solar Probe (PSP) have shown that they are a prevalent feature of the near-Sun solar wind. However, observations of switchbacks at 1 au and beyond are less frequent, suggesting that these structures evolve and potentially erode as they propagate away from the Sun. The specific mechanisms at play have not been identified thus far. Aims. We search for magnetic switchbacks undergoing magnetic reconnection, characterise them, and evaluate the viability of reconnection as a possible channel for their erosion. Methods. We analysed magnetic field and plasma data from the Magnetometer and Solar Wind Analyser instruments aboard Solar Orbiter collected between 10 August and 30 August 2021. During this period, the spacecraft was 0.6–0.7 au from the Sun. Using hodographs and Walén analysis methods, we tested for rotational discontinuities (RDs) in the magnetic field and reconnection-associated outflows at the boundaries of the identified switchback structures. Results. We identified three instances of reconnection occurring at the trailing edge of magnetic switchbacks, with properties that are consistent with existing models of reconnection in the solar wind. Based on these observations, we propose a scenario through which reconnection can erode a switchback and we estimated the timescales for these occurrences. For our events, the erosion timescales are much shorter than the expansion timescale. Thus, the complete erosion of all three observed switchbacks would occur well before they reach 1 au. Furthermore, we find that the spatial scale of these switchbacks would be considerably larger than is typically observed in the inner heliosphere if the onset of reconnection occurs close to the Sun. Our results suggest that the onset of reconnection must occur during transport in the solar wind in the cases we consider here. These results suggest that reconnection can contribute to the erosion of switchbacks and may explain the relative rarity of switchback observations at 1 au.
The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilize the extensive suite of remote-sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote-sensing and in situ measurements of slow wind originating at open–closed magnetic field boundaries. The SOOP ran just prior to Solar Orbiter’s first close perihelion passage during two remote-sensing windows (RSW1 and RSW2) between 2022 March 3–6 and 2022 March 17–22, while Solar Orbiter was at respective heliocentric distances of 0.55–0.51 and 0.38–0.34 au from the Sun. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low-latency in situ data and full-disk remote-sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Postobservation analysis using the magnetic connectivity tool, along with in situ measurements from MAG and SWA/PAS, showed that slow solar wind originating from two out of three of the target regions arrived at the spacecraft with velocities between ∼210 and 600 km s−1. The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.