Recent observations from Solar Orbiter have emphasised the importance of small and short-lived phenomena in the solar atmosphere. They have shown small extreme-ultraviolet brightenings in the solar corona, which appear very frequently. Previously, Parker Solar Probe has revealed a highly dynamic structure in the solar wind’s magnetic field, which are referred to as switchbacks. Those results raise the question of the importance of small-scale phenomena and their potential contribution to the solar wind. We have analysed 14 coronal upflows, which were derived as blue shifts in spectroscopic data and examined the potential sources for each upflow. This was done by using Hinode/EIS rasters and calculating the Doppler velocities for the Fe XII line. Events, which are stronger blue-shifted than -6 km/s were extracted. We could identify sources for 12 out of 14 events in SDO/AIA data in all extreme-ultraviolet wavelength bands. Seven events are connected to small-scale sources, which either show faint brightenings or weak eruptions. Those small-scale features usually last for less than 25 minutes. In a last step those events were examined in Hinode/XRT and SDO/HMI data to get a better understanding. Our work has shown that even small-scale features, which are at the resolution limit of previous instruments can cause strong upflows. This underlines the importance of upcoming results from Solar Orbiter. The driving mechanisms and potential contribution of those strong small-scale upflows to the solar wind however is not understood yet.
- “Probing Upflowing Regions in the Quiet Sun and Coronal Holes”: Schwanitz, C., Harra, L., Raouafi, N. E., et al. 2021, Solar Physics, 296, 175