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

TL;DR

This study addresses how coronal propagating disturbances (PDs) trace the magnetic topology of the low corona by cross-comparing PD velocity fields derived from HRIEUV (174 Å) and AIA (171 Å). Using Time-Normalised Optical Flow (TNOF) with height-optimised Carrington mapping, the authors extract velocity fields from a quiet-Sun region containing a filament channel and an equatorial coronal hole, and they quantify how PD speeds and patterns differ with viewing height. The key findings show good overall agreement between the two viewpoints, with the coronal hole exhibiting higher PD speeds and long, cross-hole velocity lines consistent with closed-loop connectivity, while the filament shows PDs aligned along its spine; PFSS models support some of these topologies but fail to reproduce filament field geometry. These results demonstrate the viability of multi-view PD velocity mapping to constrain coronal magnetic topology and motivate applying this approach to additional datasets and integrating complementary diagnostics to achieve a 3D perspective.

Abstract

Small-scale propagating disturbances (PD) are ubiquitous in the solar corona. Time-Normalised Optical Flow (TNOF) is a method developed for mapping PD velocity fields in time series of Extreme-Ultraviolet (EUV) images. We show PD velocity fields of a quiet Sun (QS) region containing a small coronal hole (CH) and filament channel (FC) jointly observed by Extreme Ultraviolet Imager (EUI) aboard the Solar Orbiter and Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The QS observations acquired on 28 October 2023 in 174A channel of High Resolution EUV Imager (HRIEUV) of EUI and 171A channel of AIA are used. During the time of the observations, the separation angle between Solar Orbiter and SDO was approximately 26\de. A novel image alignment analysis shows that the dominant formation heights are 11.4Mm for HRIEUV and 4Mm for AIA. Despite this height difference, the PD velocity fields obtained from the observations from the two instruments are in good agreement across the region. In the QS the median PD speed is around 6.7 and 7.4\kms\ for HRIEUV and AIA respectively, with maximum speeds of around 40\kms. The small equatorial CH is a region dominated by a low temperature of $\approx$0.8MK and is host to high PD speeds, with a median speed of 17\kms. The velocity field bridges coherently across the CH from neighbouring QS regions from east to west, thus the CH must 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 may be due to the longevity of the CH, allowing time for interchange reconnection with neighbouring closed-field regions. The FC is observed to be multithermal, with a narrow central strip of high emission at both low (0.8MK) and high (2.5MK) temperatures and low emission at warm (1.2MK) temperature. The FC has PD speeds similar to those of the QS.

Figures (12)

• Figure 1: Left: AIA 171Å full-disk image on 2023 October 28 14:04UT with the ROI boxed in red. This image has been processed using Multiscale Gaussian Normalisation (MGN). morgan_2014_multiscale Right: Illustration from the Solar-MACH tool gieseler_2023_solarmach where the location of the Earth/SDO marked by (1) and Solar Orbiter marked by (2) relative to Sun is shown.
• Figure 2: (a) TSM or the magnitude of the translational pixel shift between the HRIEUV and AIA images after remapping to Carrington longitude-latitude coordinates, as a function of height for HRIEUV ($x$-axis) and AIA ($y$-axis). These heights describe the surface used to map to spherical coordinates, and are shown in both $R_{\odot}$ and Mm. The cross shows the minimum of the surface. (b) and (c) show TSM as a function of height for cuts passing through the minimum point, shown by the dotted horizontal and vertical lines in (a).
• Figure 3: The ROI as observed by (a) HRIEUV and (b) AIA. For display purposes, these images have been processed using MGN. The images are mapped into Carrington coordinates to better compare features observed from the two viewpoints. The yellow contour bounds a transequatorial CH, and the filament is labelled with a cyan contour. (c) A comparison of the segmented filament and CH regions from both instruments with the filament in dark blue contours (HRIEUV) and cyan (AIA), and the CH in orange (HRIEUV) and yellow (AIA).
• Figure 4: Results of a Differential Emission Measure (DEM) analysis of the ROI at four selected temperatures (a) 0.8, (b) 1.2, (c) 1.6, and (d) 2.5 MK. These plots show the Fractional Emission Measure (FEM), which is the emission at a given temperature divided by the total emission (integrated over all temperatures) at that pixel expressed as a percentage as shown in the colour bars.
• Figure 5: The TNOF velocity vector field for the (a) HRIEUV 174Å and (b) AIA 171Å channel. The fieldlines have a rainbow colour scheme to indicate propagation direction, with a field line starting with the colour red, and advancing through yellow, green, and ending in blue. The background image is the original intensity image with MGN processing.