Enhanced Non-Thermal Line Broadening inside Coronal Cavities above Solar Prominences revealed by Spectral Imaging CoronaGraph

TL;DR

This work addresses how non-thermal line broadening and velocity structure manifest inside coronal cavities associated with solar prominences. Using spectroscopic imaging from the Spectral Imaging Coronagraph (SICG) and CHASE, together with SDO/AIA, the authors map Doppler shifts and non-thermal velocities in two cavities, deriving temperatures via DEM and interpreting line broadening in terms of wave/turbulence activity. They find asymmetric, ring-like Doppler patterns and significantly higher non-thermal velocities inside cavities—especially in cores above prominences—consistent with enhanced MHD waves and turbulence, likely driven by prominence–corona interactions and magnetic flux-rope topology. These results provide direct evidence for intensified fluctuations within cavities and demonstrate the diagnostic power of SICG for probing pre-eruption coronal dynamics and heating processes.

Abstract

Coronal cavities, often associated with prominences, are crucial structures in understanding coronal heating and the eruption mechanism of Coronal Mass Ejections (CMEs). Previous studies have identified their lower density, higher temperature, and flux rope structures. However, spectroscopic observations are still relatively scarce. In this study, we utilize the newly developed Spectral Imaging Coronagraph (SICG), Chinese H$α$ Solar Explorer (CHASE), and AIA/SDO to analyze the morphology, temperature, Doppler shift, and non-thermal velocity of two coronal cavities observed on November 13, 2024. We find that coronal cavities are distinctly visible in SICG \ion{Fe}{14} 5303~Å and AIA 193~Å, whereas they are nearly absent in SICG \ion{Fe}{10} 6374~Å and AIA 171~Å. The spectroscopic measurements show that the two coronal cavities display asymmetric, ring-like structures in the \ion{Fe}{14} 5303~Å Doppler shift maps. The non-thermal velocities inside coronal cavities are significantly higher than those of the surrounding streamer areas. In addition, the core regions of coronal cavities, located directly above the prominences, exhibit the highest non-thermal velocities and Doppler velocities. Our results suggest the presence of waves and turbulence in coronal cavities, which are likely more intense than those in the adjacent streamer regions. We suggest that the interaction and exchange between the cold, dense prominence materials and the hot, low-density coronal materials are the main drivers of the waves and turbulence inside coronal cavities.

Figures (4)

• Figure 1: Coronal images taken by SICG and SDO/AIA on November 13, 2024. The AIA 171 Å and AIA 193 Å images are shown in panels (a) and (b). The Fe10 6374 Å and Fe14 5303 Å central wavelength images are shown in panels (c) and (d). The white boxes highlight the position of the two coronal cavities. The images have been processed to enhance contrast and highlight fine structures inside the coronal cavity and surrounding regions.
• Figure 2: The spectral properties of the north-east coronal cavity. The central wavelength intensity, Doppler velocity, and non-thermal velocity maps of the north-east coronal cavity derived from SICG Fe14 5303 Å are shown in panels (a), (b), and (c). The AIA 193 Å image is shown in panel (d). The HIS H$\alpha$ line-center image is shown in panel (e), illustrating the spatial relationship between the coronal cavity, core region, and prominence. In panels (d) and (e), the positions of the SICG occulter are indicated by white dash-dotted lines. In panels (a), (b), (c), (d), and (e), the boundaries of the coronal cavities and core regions are marked with dashed lines, and the white boxes denote streamer regions near the coronal cavities. The histograms of non-thermal velocity distributions for streamers (blue), whole cavities (black, including the core), and core regions (red) are shown in panels (f).
• Figure 3: Same as Figure 2 but for the south-east coronal cavity.
• Figure A.1: The structures on SICG Fe10 6374 Å, AIA 171 Å and temperatures of north-east (top row) and south-east (bottom row) coronal cavities. The intensity maps of the SICG Fe10 6374 Å central wavelength are shown in panels (a) and (d). The AIA 171 Å images are shown in panels (b) and (e). The temperature maps derived from DEM method are shown in panels (c) and (f). In panels (b), (c), (e) and (f), the positions of the SICG occulter are indicated by white/black dash-dotted lines. The boundaries of the coronal cavities and core regions are marked with dashed lines, and the white boxes denote streamer regions near the two cavities.