Dartmouth Events

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 and
interchange reconnection. 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 NASA Parker Solar Probe (PSP) spacecraft 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’ 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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