Study of Plasma Heating Processes in a Coronal Mass Ejection–driven Shock Sheath Region Observed with the Metis Coronagraph
Susino, Roberto; Fineschi, Silvano; Stangalini, Marco; Grimani, Catia; Giordano, Silvio; Liberatore, Alessandro; Romoli, Marco; Andretta, Vincenzo; Da Deppo, Vania; Heinzel, Petr; Naletto, Giampiero; Nicolini, Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Burtovoi, Aleksandr; De Leo, Yara; Jerse, Giovanna; Landini, Federico; Pancrazzi, Maurizio; Sasso, Clementina; Uslenghi, Michela; Frassati, Federica; Mancuso, Salvatore; Bemporad, Alessandro; Romano, Paolo; Zangrilli, Luca; Russano, Giuliana; Guglielmino, Salvo
Italy, Germany, Česko, Poland, United States
Abstract
On 2021 September 28, a C1.6 class flare occurred in active region NOAA 12871, located approximately at 27°S and 51°W on the solar disk with respect to Earth's point of view. This event was followed by a partial halo coronal mass ejection (CME) that caused the deflection of preexisting coronal streamer structures, as observed in visible-light coronagraphic images. An associated type II radio burst was also detected by both space- and ground-based instruments, indicating the presence of a coronal shock propagating into interplanetary space. By using H I Lyα (121.6 nm) observations from the Metis coronagraph on board the Solar Orbiter mission, we demonstrate for the first time the capability of UV imaging to provide, via a Doppler dimming technique, an upper limit estimate of the evolution of the 2D proton kinetic temperature in the CME-driven shock sheath as it passes through the field of view of the instrument. Our results suggest that over the 22 minutes of observations, the shock propagated with a speed decreasing from about 740 ± 110 km s‑1 to 400 ± 60 km s‑1. At the same time, the postshock proton temperatures peaked at latitudes around the shock nose and decreased with time from about 6.8 ± 1.01 MK to 3.1 ± 0.47 MK. The application of the Rankine–Hugoniot jump conditions demonstrates that these temperatures are higher by a factor of about 2–5 than those expected from simple adiabatic compression, implying that significant shock heating is still going on at these distances.