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Paper: New Insights on Penumbra Magneto-Convection
Volume: 526, Solar Polarization Workshop 8
Page: 261
Authors: Bello González, N.; Jurčák, J.; Schlichenmaier, R.; Rezaei, R.
Abstract: Fully-fledged penumbrae are a well characterised phenomenon from an observational point of view. Also, MHD simulations reproduce the observed characteristics and provide us with insights on the physical mechanisms possibly running behind the observed processes. Yet, how this penumbral magneto-convection sets in is still an open question. Due to the fact that penumbra formation is a relatively fast process (of the order of hours), it has eluded its observation with sufficient spatial resolution by both space- and ground-based solar observatories. Only recently, some researchers have witnessed the onset of both orphan and sunspot penumbrae in detail. We are one of those. In July 2009, we observed the early stages of the NOAA 11024 AR leading sunspot while developing its penumbra. The spectro-polarimetric dataset lead us to new observational findings. In this contribution, we put into context our and other authors' results to draw the overall picture of sunspot formation. Most important, the comparison on the properties of different types of penumbrae lead us to the conclusion that the formation of penumbrae is not just one mechanism. While the sole cause necessary for penumbral magneto-convection is a stably inclined magnetic field, observations show that inclined fields can be caused by flux emergence, to form orphan penumbrae, or by field lines transported down from upper photospheric layers, to form sunspot penumbra. This conclusion, together with the recent findings by Jur\čák and collaborators on a canonical value of the vertical component of the magnetic field blocking the action of penumbral magneto-convection in umbral areas, is a crucial step forward towards the understanding of the coupling of solar plasmas and magnetic fields in penumbral atmospheres.
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