Simulating the Ring-shaped Line-of-sight Flows in Prominence-cavity Systems

Abstract Line-of-sight oriented flows with several red and blue Doppler-shifted rings in coronal cavities have been observed by the Coronal Multi-channel Polarimeter (CoMP) but rarely explained. In this paper, we perform pseudo-3D simulations with a Titov–Démoulin-modified magnetic flux rope (MFR) to study the corresponding flows in coronal cavities by forward modeling. Two types of field-aligned flows are found. The first type is converging flows, which are located in the magnetic field lines near the MFR axis, converging toward the magnetic dips and driven by the filament condensation, corresponding to the inner flows. The second type is unidirectional flows, which are located in the magnetic field lines near the MFR boundary, flowing from one footpoint to the other, and are driven by the asymmetric heating, corresponding to the outer flows. These inner and outer flows naturally form a nested structure with a velocity of several km s −1 , leading to the formation of multiple rings observed in the cavity view. Synthetic Doppler images indicate two to four rings in our simulations, which is consistent with most of the observational situations by CoMP.