Professor James Drake, Institute for Physical Science and Technology, University of Maryland The mechanism that drives the solar wind has been a topic
of extensive scientific debate since the 1960's when the existence of
the solar wind was confirmed with spacecraft observations. In its
recent closest approaches to the sun the Parker Solar Probe (PSP)
spacecraft is revealing wind structure not seen by spacecraft at
1AU. The bursty radial flows and associated local reversals of the
radial magnetic field (switchbacks) exhibit a spatial periodicity that
is linked to that of network magnetic field near the solar surface
(Bale et al. 2021; ApJ 923,174). The observations point to magnetic reconnection between open and closed magnetic flux in coronal holes (interchange reconnection) as the driver of these bursts. The corresponding enhancements in plasma pressure, wind speed, and energetic ions further suggest that interchange reconnection is the fundamental source of energy that drives the fast solar wind. We use the PSP data along with the basic characteristics of reconnection to deduce the local properties of interchange reconnection near the solar surface,
including the characteristic strength of the reconnecting magnetic,
the ambient density, the rate of reconnection and associated rate of
energy release (Bale et al. 2023; Nature, vol. 628). An important conclusion of the analysis is that coronal interchange reconnection is in the collisionless regime and that the energy released by interchange reconnection is sufficient to drive the wind. Analytical estimates are supported by particle-in-cell simulations of interchange reconnection that
establish that the structure of reconnection exhausts match PSP
measurements. The spectra of energetic protons and alpha particles
from the simulations, which take the form of powerlaws at high energy,
also match the observations by the PSP. The bursty nature of
interchange reconnection has implications for the development of the
measured turbulence in the solar wind, which is currently being
explored. These results have significant implications for
understanding the winds produced by objects throughout the universe.
Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During his visit to Heidelberg, Professor Drake will be available for meetings by arrangement with his host, Brian Reville (brian.reville@mpi-hd.mpg.de)
