Search for: All records

Abstract This study presents observations of a large pseudostreamer solar eruption and, in particular, the post-eruption relaxation phase, as captured by Metis, on board the Solar Orbiter, on 2022 October 12, during its perihelion passage. Utilizing total-brightness data, we observe the outward propagation of helical features up to 3 solar radii along a radial column that appears to correspond to the stalk of the pseudostreamer. The helical structures persisted for more than 3 hr following a jet-like coronal mass ejection associated with a polar crown prominence eruption. A notable trend is revealed: the inclination of these features decreases as their polar angle and height increase. Additionally, we measured their helix pitch. Despite the 2 minute time cadence limiting direct correspondence among filamentary structures in consecutive frames, we find that the Metis helical structure may be interpreted as a consequence of twist (nonlinear torsional Alfvén waves) and plasma liberated by interchange reconnection. A comparison was performed between the helix parameters as outlined by fine-scale outflow features and those obtained from synthetic white-light images derived from the high-resolution magnetohydrodynamics simulation of interchange reconnection in a pseudostreamer topology by P. F. Wyper et al. A remarkable similarity between the simulation-derived images and the observations was found. We conjecture that these Metis observations may represent the upper ends of the spatial and energy scales of the interchange reconnection process that has been proposed recently as the origin of the Alfvénic solar wind. 

Context. The fast solar wind is known to emanate from polar coronal holes. Aims. This Letter reports the first estimate of the expansion rate of polar coronal flows performed by the Metis coronagraph on board Solar Orbiter. Methods. By exploiting simultaneous measurements in polarized white light and ultraviolet intensity of the neutral hydrogen Lyman- α line, it was possible to extend observations of the outflow velocity of the main component of the solar wind from polar coronal holes out to 5.5  R ⊙ , the limit of diagnostic applicability and observational capabilities. Results. We complement the results obtained with analogous polar observations performed with the UltraViolet Coronagraph Spectrometer on board the SOlar and Heliospheric Observatory during the previous full solar activity cycle, and find them to be satisfactorily reproduced by a magnetohydrodynamic turbulence model. Conclusions. This suggests that the dissipation of 2D turbulence energy is a viable mechanism for coronal plasma heating and the subsequent acceleration of the fast solar wind. 

Aims. Our aim is to investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere. Observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses. Methods. Quiet-Sun and weak-plage regions were observed in the Ca  II 854.2 nm and H α lines with the Fast Imaging Solar Spectrograph (FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and in the H α and H β lines with the echelle spectrograph attached to the Vacuum Tower Telescope on 2018 December 11 and 2019 June 6. The deposited acoustic energy flux at frequencies up to 20 mHz was derived from Doppler velocities observed in line centers and wings. Radiative losses were computed by means of a set of scaled non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models obtained by fitting synthetic to observed line profiles. Results. In the middle chromosphere ( h = 1000–1400 km), the radiative losses can be fully balanced by the deposited acoustic energy flux in a quiet-Sun region. In the upper chromosphere ( h  >  1400 km), the deposited acoustic flux is small compared to the radiative losses in quiet as well as in plage regions. The crucial parameter determining the amount of deposited acoustic flux is the gas density at a given height. Conclusions. The acoustic energy flux is efficiently deposited in the middle chromosphere, where the density of gas is sufficiently high. About 90% of the available acoustic energy flux in the quiet-Sun region is deposited in these layers, and thus it is a major contributor to the radiative losses of the middle chromosphere. In the upper chromosphere, the deposited acoustic flux is too low, so that other heating mechanisms have to act to balance the radiative cooling.