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1. Verifying Interchange Reconnection Models for Magnetic Switchbacks Using the Parker Solar Probe and MMS

   McDougall, Emily (September 2025, University of New Hampshire Scholars Repository)

   Ever since their initial observation by the Ulysses probe, many models of magnetic switchbacks were put forth, but relatively little empirical evidence exists to verify these models, especially in terms of the ions that make up the accompanying plasma. I take energetic particle data from the Parker Solar Probe within switchbacks to provide experimental evidence to bolster the interchange reconnection driven models with particular interest in the interchange reconnection driven linear model. Statistical Analysis of switchbacks in the vicinity of CMEs, solar flares, and high-speed streams show properties consistent with the linear interchange reconnection model, and an analysis of switchbacks in a Twin-CME event displays evidence of switchbacks being produced by reconnection. Additionally, I observe a switchback in the magnetosheath using MMS and obtain evidence that it was formed by interchange reconnection at the magnetopause. 

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2. Direct evidence for magnetic reconnection at the boundaries of magnetic switchbacks with Parker Solar Probe

   https://doi.org/10.1051/0004-6361/202039806  

   Froment, C.; Krasnoselskikh, V.; Dudok de Wit, T.; Agapitov, O.; Fargette, N.; Lavraud, B.; Larosa, A.; Kretzschmar, M.; Jagarlamudi, V. K.; Velli, M.; et al (June 2021, Astronomy & Astrophysics)

   Context. The first encounters of Parker Solar Probe (PSP) with the Sun revealed the presence of ubiquitous localised magnetic deflections in the inner heliosphere; these structures, often called switchbacks, are particularly striking in solar wind streams originating from coronal holes. Aims. We report the direct piece of evidence for magnetic reconnection occurring at the boundaries of three switchbacks crossed by PSP at a distance of 45 to 48 solar radii to the Sun during its first encounter. Methods. We analyse the magnetic field and plasma parameters from the FIELDS and Solar Wind Electrons Alphas and Protons instruments. Results. The three structures analysed all show typical signatures of magnetic reconnection. The ion velocity and magnetic field are first correlated and then anti-correlated at the inbound and outbound edges of the bifurcated current sheets with a central ion flow jet. Most of the reconnection events have a strong guide field and moderate magnetic shear, but one current sheet shows indications of quasi anti-parallel reconnection in conjunction with a magnetic field magnitude decrease by 90%. Conclusions. Given the wealth of intense current sheets observed by PSP, reconnection at switchback boundaries appears to be rare. However, as the switchback boundaries accomodate currents, one can conjecture that the geometry of these boundaries offers favourable conditions for magnetic reconnection to occur. Such a mechanism would thus contribute in reconfiguring the magnetic field of the switchbacks, affecting the dynamics of the solar wind and eventually contributing to the blending of the structures with the regular wind as they propagate away from the Sun. 

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3. Energetic Ion Composition as a Means of Investigating the Physical Origins of Alpha Particle Heavy Magnetic Switchbacks

   https://doi.org/10.3847/1538-4357/adc2ff  

   McDougall, Emily; Poduval, Bala (April 2025, The Astrophysical Journal)

   Abstract Magnetic switchbacks are of continuing interest to the scientific community because the phenomenon has not been completely understood. Although most of the research into them in the Parker Solar Probe era has largely focused on creating a theoretical framework for causing the field reversal through magnetic interchange reconnection, reconnecting streams of plasma in the solar wind, or shear driven turbulence, it remains unclear as to what extent these models may or may not represent the underlying physical reality of magnetic switchbacks. In this paper, we present the results of our study on the energetic ion composition of magnetic switchback events using statistical methods with the aim of obtaining new insights into the underlying physics. In doing so, we find evidence that switchbacks containing suprathermal alpha flux display traits that are indicative of the Zank model of a magnetic “kink” propagating as a fast magnetosonic wave. These switchbacks also correlated with increased solar activity such as coronal mass ejections, high-speed streams, and solar flares. At the same time, switchbacks not meeting this criteria appear to occur at rates that are unaffected by increasing solar activity, which implies the existence of multiple populations of switchbacks with differing physical mechanisms behind them. 

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4. Interchange reconnection as the source of the fast solar wind within coronal holes

   https://doi.org/10.1038/s41586-023-05955-3  

   Bale, S. D.; Drake, J. F.; McManus, M. D.; Desai, M. I.; Badman, S. T.; Larson, D. E.; Swisdak, M.; Horbury, T. S.; Raouafi, N. E.; Phan, T.; et al (June 2023, Nature)

   Abstract The fast solar wind that fills the heliosphere originates from deep within regions of open magnetic field on the Sun called ‘coronal holes’. The energy source responsible for accelerating the plasma is widely debated; however, there is evidence that it is ultimately magnetic in nature, with candidate mechanisms including wave heating 1,2 and interchange reconnection 3–5 . The coronal magnetic field near the solar surface is structured on scales associated with ‘supergranulation’ convection cells, whereby descending flows create intense fields. The energy density in these ‘network’ magnetic field bundles is a candidate energy source for the wind. Here we report measurements of fast solar wind streams from the Parker Solar Probe (PSP) spacecraft 6 that provide strong evidence for the interchange reconnection mechanism. We show that the supergranulation structure at the coronal base remains imprinted in the near-Sun solar wind, resulting in asymmetric patches of magnetic ‘switchbacks’ 7,8 and bursty wind streams with power-law-like energetic ion spectra to beyond 100 keV. Computer simulations of interchange reconnection support key features of the observations, including the ion spectra. Important characteristics of interchange reconnection in the low corona are inferred from the data, including that the reconnection is collisionless and that the energy release rate is sufficient to power the fast wind. In this scenario, magnetic reconnection is continuous and the wind is driven by both the resulting plasma pressure and the radial Alfvénic flow bursts. 

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5. A Solar Source of Alfvénic Magnetic Field Switchbacks: In Situ Remnants of Magnetic Funnels on Supergranulation Scales

   https://doi.org/10.3847/1538-4357/ac2d8c  

   Bale, S. D.; Horbury, T. S.; Velli, M.; Desai, M. I.; Halekas, J. S.; McManus, M. D.; Panasenco, O.; Badman, S. T.; Bowen, T. A.; Chandran, B. D.; et al (December 2021, The Astrophysical Journal)

   Abstract One of the striking observations from the Parker Solar Probe (PSP) spacecraft is the prevalence in the inner heliosphere of large amplitude, Alfvénic magnetic field reversals termed switchbacks . These δ B R / B ∼  ( 1 ) fluctuations occur over a range of timescales and in patches separated by intervals of quiet, radial magnetic field. We use measurements from PSP to demonstrate that patches of switchbacks are localized within the extensions of plasma structures originating at the base of the corona. These structures are characterized by an increase in alpha particle abundance, Mach number, plasma β and pressure, and by depletions in the magnetic field magnitude and electron temperature. These intervals are in pressure balance, implying stationary spatial structure, and the field depressions are consistent with overexpanded flux tubes. The structures are asymmetric in Carrington longitude with a steeper leading edge and a small (∼1°) edge of hotter plasma and enhanced magnetic field fluctuations. Some structures contain suprathermal ions to ∼85 keV that we argue are the energetic tail of the solar wind alpha population. The structures are separated in longitude by angular scales associated with supergranulation. This suggests that these switchbacks originate near the leading edge of the diverging magnetic field funnels associated with the network magnetic field—the primary wind sources. We propose an origin of the magnetic field switchbacks, hot plasma and suprathermals, alpha particles in interchange reconnection events just above the solar transition region and our measurements represent the extended regions of a turbulent outflow exhaust. 

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