The Sun's Dynamic Extended Corona Observed in Extreme Ultraviolet

TL;DR

This paper presents new EUV observations of the middle solar corona, revealing its dominant resonant scattering emission, complex dynamics influencing solar wind and eruptions, and providing critical data to improve models of the corona-heliosphere connection.

Contribution

It offers the first comprehensive EUV observational analysis of the middle corona, highlighting its emission mechanisms, dynamics, and role in solar wind and eruption initiation, filling a key knowledge gap.

Findings

Resonant scattering dominates emission in the middle corona.

Solar wind structures originate from complex dynamics in this region.

Kinematic profiles of coronal mass ejections are now characterized.

Abstract

The "middle corona" is a critical transition between the highly disparate physical regimes of the lower and outer solar corona. Nonetheless, it remains poorly understood due to the difficulty of observing this faint region (1.5-3 solar radii). New observations from the GOES Solar Ultraviolet Imager in August and September 2018 provide the first comprehensive look at this region's characteristics and long-term evolution in extreme ultraviolet (EUV). Our analysis shows that the dominant emission mechanism here is resonant scattering rather than collisional excitation, consistent with recent model predictions. Our observations highlight that solar wind structures in the heliosphere originate from complex dynamics manifesting in the middle corona that do not occur at lower heights. These data emphasize that low-coronal phenomena can be strongly influenced by inflows from above, not only by photospheric motion, a factor largely overlooked in current models of coronal evolution. This study reveals the full kinematic profile of the initiation of several coronal mass ejections, filling a crucial observational gap that has hindered understanding of the origins of solar eruptions. These new data uniquely demonstrate how EUV observations of the middle corona provide strong new constraints on models seeking to unify the corona and heliosphere.