Parker Solar Probe Observations of Magnetic Reconnection Exhausts in Quiescent Plasmas near the Sun

Abstract

Parker Solar Probe observations are analyzed for the presence of reconnection exhausts across current sheets (CSs) within R < 0.26 au during encounters 4–11. Exhausts are observed with nearly equal probability at all radial distances with a preference for quiescent Tp < 0.80 MK plasmas typical of a slow-wind regime. High Tp > 0.80 MK plasmas of a fast wind characterized by significant transverse fluctuations rarely support exhausts irrespective of the CS width. Exhaust observations demonstrate the presence of local temperature gradients across several CSs with a higher-Tp plasma on locally closed fields and a lower-Tp plasma on locally open field lines for an interchange-type reconnection. A CS geometry analysis directly supports the property that X-lines bisect the magnetic field rotation θ-angle, whether the fields and plasmas are asymmetric or not, to maximize reconnection rates and available magnetic energy. The CS normal width d cs distributions suggest that a multiscale reconnection process through nested layers of bifurcated CSs may be responsible for observed power-law distributions beyond the median d cs ∼ 1000 km with an exponential d cs distribution present for ion kinetic dissipation scales below this median. Magnetic field shear θ-angles are essentially identical at R < 0.26 and 1 au with medians at θ ∼ 55° near the Sun and θ ∼ 65° at 1 au. In contrast, the tangential flow shear distributions are different near and far from the Sun. A bimodal flow shear angle distribution is present near the Sun with strong shear flow magnitudes. This distribution is modified with radial distance toward a relatively flat distribution of weaker flow shear magnitudes.

Frequency-dispersed Ion Acoustic Waves in the Near-Sun Solar Wind: Signatures of Impulsive Ion Beams

“…Also, magnetic reconnection events are known to produce proton beams in the near-Sun solar wind (Lavraud et al 2021;Phan et al 2022), and studies have demonstrated that magnetic reconnection occurs throughout the near-Sun solar wind (e.g., (Phan et al 2020;Fargette et al 2023;Eriksson et al 2024). If the frequency-dispersed ion acoustic waves reported here are driven by proton beams associated with magnetic reconnection, then the wave observations may help constrain the spatial density of magnetic reconnection in the near-Sun solar wind, which in turn may help constrain its importance as an energy input to the solar wind (Gosling et al 2006a(Gosling et al , 2006b.…”