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EP: Fachverband Extraterrestrische Physik
EP 9: Poster
EP 9.14: Poster
Wednesday, March 22, 2023, 17:30–19:00, HSZ OG1
Flux-rope nonequilibrium in the slow-rise phase of solar eruptions — •Bernhard Kliem — Universität Potsdam, Institut für Physik und Astronomie
Solar eruptions are nearly always preceded by a slow-rise phase that comprises an ascent of the eventually erupting filament (or prominence) in the corona and a slow increase of the soft X-ray flux. This is a distinct phase characterized by intermediate velocities of typically several 10 km s−1 (in active regions up to ∼ 100 km s−1), 1–2 orders of magnitude faster than the quasi-static evolution during energy storage, which scales with the driving photospheric velocities, and 1.5–3 orders of magnitude below the coronal Alfvén velocity, VA, which is the scaling parameter of eruption speeds and their upper limit. Proposed mechanisms of this phase range from distributed small-scale (“tether-cutting”) reconnection events in sheared field to a nonequilibrium and even ideal magnetohydrodynamic instability of a flux rope. I present simulations of flux cancellation that show the formation of a flux rope, a quasi-static evolution with a rise speed similar to the imposed photospheric driver, then a slightly faster rise, gradually accelerating up to ≈ 10−2 VA, and eventually the eruption of the rope by onset of the torus instability. The flux rope is shown to be in a nonequilibrium state during the slow rise.