The Role of Thermal Nonequilibrium in Driving the Corona-Heliosphere Connection

Recent observations have shown that the coupling between the corona and heliosphere is intrinsically dynamic with quasi-periodic density structures ubiquitously seen in those solar wind regions that map down to the vicinity of the open-closed boundary. Given their quasi-periodic nature, a promising explanation for the formation of these structures is thermal nonequilibrium (TNE), a process by which solar coronal loops undergo quasi-periodic cycles of heating and cooling due to the spatial localization of coronal heating near the loop base. Since the requirement for TNE onset is that the loop length is large compared to the scale of the heating, it is most likely to occur on the largest coronal loops, those near the open-closed boundary. We use 2.5D MHD numerical simulations to investigate the effect of TNE in the corona and heliosphere of an axisymmetric helmet streamer and polar coronal holes. As in the many1D loop studies, we find that TNE occurs in coronal loops with sufficiently large length, but in contrast to previous studies, we find that the process also drives substantial magnetic dynamics, especially near the top of the streamer where the plasma beta becomes of order unity. From the simulation results we determine predictions for spectroscopic and imaging observations of both the hot and cool helmet streamer plasma and the solar wind in the vicinity of the streamer stalk. We conclude that TNE occurring in the largest closed loops in the corona may explain several puzzling observations of the corona and wind, such as the ubiquitous blue shifts observed at the edges of active regions, and the quasi-periodic solar wind structures. We also discuss the implications of our results for the upcoming PSP and SO observations.

This work was supported by the NASA Living With a Star Program.