Total Solar Eclipse Observations: A Treasure Trove from the Source and Acceleration Regions of the Solar Wind

Abstract

A comprehensive exploration of the inner corona, namely the spatial span starting from the solar surface out to a few solar radii, is essential for investigating the physical processes responsible for its quiescent and dynamic state. Such an exploration encompasses the source regions of the solar wind, and is thus essential for reliably establishing their link to in-situ measurements, including those from the more recent Parker Solar Probe mission. Total solar eclipses are the only platform available at present to fulfill these requirements, as they offer a spatially uninterrupted diagnosis of the inner corona through multi-wavelength imaging and spectroscopy. This review highlights results from almost two decades of eclipse observations. Particular emphasis is placed on the discovery of the complexity of coronal structures, in particular at the source regions of the solar wind, directly connected to prominences. Complex structures include different manifestations of waves and plasma instabilities. Imaging in coronal emission lines yields the only diagnostic tool, known to date, for the empirical inference of the freeze-in distance of heavy ions. Imaging also enables the mapping of the electron temperature in the inner corona, and its changes in response to the passage of a coronal mass ejection (CME). Furthermore, spectroscopic observations reveal that cool prominence material associated with a CME, travels in tandem, unscathed, into interplanetary space. Multi-wavelength imaging and spectroscopy during total solar eclipses thus yield a treasure trove from the sources and acceleration regions of the solar wind, which beg continued exploitation in search of signatures of coronal heating and solar wind acceleration processes.