Solar Prominence Merging

Abstract

In a recent paper, we described MHD simulations of the interaction between a pair of distinct prominences formed by the photospheric line-tied shearing of two separated dipoles. One case was typical of solar observations of prominence merging, in which the prominences have the same axial field direction and sign of magnetic helicity. For that configuration, we reported the formation of linkages between the prominences due to magnetic reconnection of their sheared fields. In this paper, we analyze the evolution of the plasma-supporting magnetic dips in this configuration. As the photospheric flux is being progressively sheared, dip-related chromospheric fibrils and high-altitude threads form and develop into the two prominences, which undergo internal oscillations. As the prominences are stretched farther along their axes, they come into contact and their sheared fluxes pass each other, and new dips form in the interaction region. The distribution of these dips increasingly fills the volume between the prominences, so that the two progenitors gradually merge into a single prominence. Our model reproduces typical observational properties reported from both high-cadence and daily observations at various wavelengths. We identify the multistep mechanism, consisting of a complex coupling between photospheric shear, coronal magnetic reconnection without null points, and formation of quasi bald patches, that is responsible for the prominence merging through dip creation. The resulting magnetic topology differs significantly from that of a twisted flux tube.