The Emergence of Kink-Unstable Magnetic Flux Tubes and the Origin of delta -Configuration Sunspots

Details The Emergence of Kink-Unstable Magnetic Flux Tubes and the Origin of delta -Configuration Sunspots The Emergence of Kink-Unstable Magnetic Flux Tubes and the Origin of delta -Configuration Sunspots

May 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...194.5903f&link_type=abstract

American Astronomical Society, 194th AAS Meeting, #59.03; Bulletin of the American Astronomical Society, Vol. 31, p.918

Astronomy and Astrophysics

Astronomy

Scientific paper

The so-called delta -configuration sunspots are an unusual class of compact sunspots in which umbrae of opposite polarities are gathered closely in a common penumbra, and the polarity order is often inverted from Hale's polarity law. One appealing suggestion for the origin of the delta -spots, is that they are formed through the emergence of flux tubes that have become kinked (or knotted) due to the onset of the current driven kink instability. In this talk I present 3D simulations of the non-linear evolution of the helical kink instability of twisted magnetic flux tubes rising buoyantly through an adiabatically stratified layer. We study the kink evolution of buoyant flux tubes with a range of different initial twist. We find that in order for the tube to develop significant kinking during its rise, the initial twist of the tube needs to be close to or greater than the critical limit for the onset of the kink instability. If the initial twist is sufficiently super-critical such that the e-folding period of the fastest growing kink mode is small compared to the rise time of the tube, we find that sharp bending and distortion of the tube develop. Due to the effect of gravitational stratification, the kinked flux tube arches upward and evolves into a buckled loop with a local change of tube orientation at the loop apex that exceeds 90(deg) from the original direction of the tube. I will discuss the similarities and differences between the structure of the buckled emerging flux loop and the magnetic field morphology of several delta -spots.

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