Formation and Characteristics of Filament Threads in Double-Dipped Magnetic Flux Tubes

TL;DR

This study uses numerical simulations to explore how filament threads form in double-dipped magnetic flux tubes, revealing conditions that favor their formation and explaining features of quiescent filaments.

Contribution

It introduces a novel analysis of filament formation in double-dipped flux tubes, extending the evaporation-condensation model beyond single-dip configurations.

Findings

Magnetically connected threads are more common in quiescent filaments.

Formation requires specific magnetic configurations and localized heating.

Threads in double-dipped tubes are shorter, explaining filament features.

Abstract

As one of the main formation mechanisms of solar filament formation, the chromospheric evaporation-coronal condensation model has been confirmed by numerical simulations to explain the formation of filament threads very well in flux tubes with single dips. However, coronal magnetic extrapolations indicated that some magnetic field lines might possess more than one dip. It is expected that the formation process would be significantly different in this case compared to a single-dipped magnetic flux tube. In this paper, based on the evaporation-condensation model, we study filament thread formation in double-dipped magnetic flux tubes by numerical simulations. We find that only with particular combinations of magnetic configuration and heating, e.g., concentrated localized heating and a long magnetic flux tube with deep dips, can two threads form and persist in a double-dipped magnetic flux tube. Comparing our parametric survey with observations, we conclude that such magnetically connected threads due to multiple dips are more likely to exist in quiescent filaments than in active-region filaments. Moreover, we find that these threads are usually shorter than independently trapped threads, which might be one of the reasons why quiescent filaments have short threads. These characteristics of magnetically connected threads could also explain barbs and vertical threads in quiescent filaments.