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

ASTROPHYSICAL JOURNAL(2024)

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摘要
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 theta-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) similar to 1000 km with an exponential d(cs) distribution present for ion kinetic dissipation scales below this median. Magnetic field shear theta-angles are essentially identical at R < 0.26 and 1 au with medians at theta similar to 55 degrees near the Sun and theta similar to 65 degrees 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.
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关键词
Solar wind,Solar magnetic reconnection
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