Magnetic reconnection as an erosion mechanism for magnetic switchbacks

Abstract

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.

Connecting Solar Wind Velocity Spikes Measured by Solar Orbiter and Coronal Brightenings Observed by SDO

“…Indeed, recent observations by the Parker Solar Probe (PSP) mission within a heliocentric distance of 0.3 au have mainly observed this solar wind regime and reveal the presence of switchbacks occurring in conjunction with velocity spikes (Bale et al 2019;Zank et al 2020;Shi et al 2022). The radial evolution of velocity and temperature within velocity spikes suggests that their dissipation contributes to the energization of the near-Sun solar wind (Froment et al 2021;Hou et al 2023;Suen et al 2023). The proton temperature anisotropy inside velocity spikes (Luo et al 2023) can provide favorable conditions for instability and wave mode excitation, including kinetic Alfvén waves (Malaspina et al 2022) and ion-acoustic waves (Mozer et al 2021), which have been observed within and near velocity spikes.…”