Small-Scale Activity Above the Penumbra of a Fast-Rotating Sunspot

Properties of the Umbral Filament Observed in Active Region NOAA 12529

“…In this context, one may investigate on the origin of brightenings observed along the UF, provided that this intruding structure could interact with the main flux systems of the sunspot. The observations reported by Bharti et al (2017Bharti et al ( , 2018 show jets and brightenings in the chromosphere and transition region above filamentary structures intruding sunspot umbrae. These phenomena have been interpreted as a result of magnetic reconnection taking place between the umbral field and the opposite-polarity patches observed along the penumbral-like intrusions, due to strong convective motions that enhance or even reverse the magnetic field.…”

“…These phenomena have been interpreted as a result of magnetic reconnection taking place between the umbral field and the opposite-polarity patches observed along the penumbral-like intrusions, due to strong convective motions that enhance or even reverse the magnetic field. However, the region studied by Bharti et al (2018) was observed in a δ spot, where the uncombed configuration of the penumbrae and the shear present in the interface region between the two opposite-polarity umbral cores may give rise to a complex magnetic and velocity field configuration (e.g., Cristaldi et al 2014;Shimizu et al 2014). We cannot exclude that such interactions may occur in the system we analyzed, although one has to keep in mind that AR 12529 was not flare-productive at all, in contrast to ARs studied by Kleint & Sainz Dalda (2013) and Bharti et al (2018).…”