Princeton Center for Heliophysics Seminar

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 likely candidate mechanisms including wave heating and interchange reconnection. The coronal magnetic field near the solar surface is known to be structured on scales associated with ‘supergranulation’ convection cells, where descending flows create intense fields. The energy density in these ‘network’ magnetic field bundles is a candidate energy source for the wind. I will show measurements of fast solar wind streams from the Parker Solar Probe (PSP) spacecraft which provides strong evidence for the interchange reconnection mechanism. We show that 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. PIC 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 both by the resulting plasma pressure enchancement and the radial Alfvénic flow bursts.