The Pre-Penumbral Magnetic Canopy in the Solar Atmosphere

Abstract

Penumbrae are the manifestation of magnetoconvection in highly inclined (to the vertical direction) magnetic field. The penumbra of a sunspot tends to form, initially, along the arc of the umbra antipodal to the main region of flux emergence. The question of how highly inclined magnetic field can concentrate along the antipodal curves of umbrae, at least initially, remains to be answered. Previous observational studies have suggested the existence of some form of overlying magnetic canopy which acts as the progenitor for penumbrae. We propose that such overlying magnetic canopies are a consequence of how the magnetic field emerges into the atmosphere and are, therefore, part of the emerging region. We show, through simulations of twisted flux tube emergence, that canopies of highly inclined magnetic field form preferentially at the required locations above the photosphere.

Continuum Enhancements, Line Profiles, and Magnetic Field Evolution during Consecutive Flares

“…Indeed, invoking such a mechanism able to lead to the presence of highly inclined, nearly horizontal magnetic fields, for being responsible for penumbra formation (or, conversely, decay) strengthens the argument which has been proposed in recent studies concerning the development of penumbrae and penumbral-like structures, from both the observational (see, e.g. Shimizu et al 2012;Lim et al 2013;Guglielmino et al 2014;Romano et al 2013Romano et al , 2014Zuccarello et al 2014;Jurčák et al 2014Jurčák et al , 2017Murabito et al 2017Murabito et al , 2018 and the theoretical point of view (Rempel 2012;MacTaggart et al 2016), even in absence of magnetic flux variations. In this perspective, our findings indicate that the effects of magnetic reconfiguration leading to penumbral enhancements driven by flares can extend well beyond the region around the flaring PILs.…”

Properties of the Umbral Filament Observed in Active Region NOAA 12529

“…Such a mechanism has been invoked to explain the formation of regular penumbrae in sunspot (Shimizu et al 2012;Romano et al 2013Romano et al , 2014, also when the penumbra formation occurs in the region of ongoing flux emergence (Murabito et al 2017(Murabito et al , 2018, as confirmed by numerical simulations (e.g. Rempel 2012;MacTaggart et al 2016). Moreover, it seems to account for the formation of other penumbral-like structures, such as orphan penumbrae, when the emerging flux is overarched by an overlying canopy (Lim et al 2013;Guglielmino et al 2014;Zuccarello et al 2014), but also when they appear as photospheric manifestations of flux ropes trapped highly in the photosphere, corresponding to chromospheric filaments (e.g., Kuckein et al 2012a,b;Buehler et al 2016).…”

The Formation and Decay of Sunspot Penumbrae in Active Region NOAA 12673

“…They thought the chromospheric threads represent the pre-existing chromospheric horizontal field during the formation of penumbra filaments and suggested the emerging flux is trapped at the photosphere by the overlying chromospheric canopy fields. The presence of magnetic canopy fields in the chromosphere before penumbra formation may be crucial for the development of penumbra evidenced by chromospheric observations (Romano et al 2013(Romano et al , 2014Guglielmino et al 2014) and simulations (Rempel 2011(Rempel , 2012MacTaggart et al 2016). However, not all events of penumbral formation is accompanied with the overlying magnetic field before their formation.…”