A multi-viewpoint comparison of the velocity field of propagating coronal disturbances

Small-scale propagating disturbances (PDs) are ubiquitous in the solar corona. The method called time-normalised optical flow (TNOF) was developed for mapping PDs velocity fields in time series of extreme-ultraviolet (EUV) images. We show PDs velocity fields of a quiet-Sun (QS) region containing a small coronal hole (CH) and filament channel (FC) that were jointly observed by Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter and Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The QS observations acquired on 28 October 2023 in the 174 Å channel of High Resolution EUV Imager (HRIEUV) of EUI and 171 Å channel of AIA were used. During the time of the observations, the separation angle between Solar Orbiter and SDO was approximately 26°. A novel image-alignment analysis shows that the dominant formation heights are 11.4 Mm for HRIEUV and 4 Mm for AIA. Despite this height difference, the PDs velocity fields obtained from the observations from the two instruments agree well throughout the region. In the QS, the median PDs speed is about 6.7 and 7.4 kms ⁻¹ for HRIEUV and AIA, respectively, with maximum speeds of about 40 kms ⁻¹. The small equatorial CH region is dominated by a low temperature of ≈0.8 MK and is host to high PDs speeds, with a median speed of 17 kms ⁻¹. The velocity field bridges coherently across the CH from neighbouring QS regions from east to west, and the CH must therefore be overlaid by a system of long, low-lying closed magnetic loops. This unexpected configuration is supported by a potential field (PF) magnetic model and might be caused by the longevity of the CH, which allows time for interchange reconnection with neighbouring closed-field regions. The FC is observed to be multi-thermal, with a narrow central high-emission strip at low (0.8 MK) and high (2.5 MK) temperatures and low emission at a warm (1.2 MK) temperature. Despite this distinct temperature profile, the PDs speeds in the FC are similar to those of the QS. The TNOF velocity field shows that PDs tend to flow into the FC from neighbouring regions before they align along the FC in a coherent direction. This means that PDs within filaments are driven by external sources. The vector field is consistent with a highly non-potential barbs-and-spine tubular magnetic field; the PF model fails to replicate this configuration. We conclude that longer magnetic loops are required for higher PDs speeds, as observed for CH here, and that the smaller loop systems of the QS and FC generally lead to lower speeds. These multi-instrument results show that the TNOF method can confidently be used as a diagnostic tool for the kinematics of PDs, and it highlights its potential for probing the coronal magnetic field orientation, particularly in highly non-potential regions, where extrapolation models may fail.