Solar Orbiter: A unique opportunity for investigating small-scale physical processes at work in the magnetic solar atmosphere Original Research Article

With knowledge gained from the recent ULYSSES, SOHO, TRACE and other missions, a great deal of progress has been made in our understanding of the structure and dynamics of the various regions of the solar atmosphere: e.g., transition region and “quiet” corona, coronal holes and active region loops. However, no clear conclusions can yet be drawn about the fundamental processes that determine the existence and the underlying physics of these regions, especially their observed high temperature and flows. The lack of adequate spatial resolution has limited the study of the continuum between cool/hot, source/sink, and magnetic/non-magnetic regions. We consider here, magnetic reconnection as an example of the basic processes that are most likely involved at many different scales in heating and particle acceleration. Starting with a possible mechanism for reconnection (flux emergence), we consider different remote-sensing signatures of reconnection: flows, field rearrangement, impulsive heating, particle acceleration, wave generation, propagation and dissipation. We discuss their small-scale properties derived from current measurements and ways to improve their observation. We also consider how remote sensing and in situ measurements could be coordinated. To demonstrate how these advances might be achieved, we discuss the potential for discoveries offered by the Solar Orbiter, resulting notably from its relatively high spatial resolution and its capacity to observe for a substantial time in co-rotation with the Sun.