Multiscale Helicity Condensation and Filament Channel Formation
Abstract
Solar eruptive events ranging from small-scale jets to global-scale coronal mass ejections are associated with filaments and their underlying filament-channel magnetic structures. In previous work, we have demonstrated that sheared-arcade filament channels can be formed via the process of helicity condensation. Magnetic twist, representing helicity, is transported across unipolar regions in response to reconnection induced by small-scale, close-packed, surface flows (e.g., the granulation or supergranulation) that possess a vortical component of motion. The small-scale twists induced by the flows inverse-cascade to the largest scales and boundaries of the unipolar regions, i.e., to the polarity inversion lines (PILs). If the flows have a preferred sense of rotation, clockwise or counter, they inject a net helicity into the magnetic field, as well as transport it so that it condenses into filament channels at the PILs. We now have examined how the helicity condensation mechanism is modified when the small-scale flows have no preferred sense of rotation, and large-scale flows are solely responsible for introducing net helicity into the corona. On the Sun, differential rotation is well-known to be a prodigious generator of helicity. Our new simulation results show that a large-scale shear flow produces structure with large-scale magnetic twist, but this twist concentrates near the PILs to form filament channels only when small-scale vortical flows also are present. We conclude that the key role of the vortical flows is to transport the injected net helicity and condense it at the PILs. The source of the net helicity, on the other hand, can be flows at any scale. We refer to this extended concept as multiscale helicity condensation: it is a more general, hence more robust, explanation for the formation of filament channels on the Sun. Our work was supported by NASA's H-ISFM, H-SR, and LWS TR&T programs.
- Publication:
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American Astronomical Society Meeting Abstracts #234
- Pub Date:
- June 2019
- Bibcode:
- 2019AAS...23410602D