Impulsive coronal heating during the interaction of surface magnetic fields in the lower solar atmosphere

Abstract

Coronal plasma in the cores of solar active regions is impulsively heated to more than 5 MK. The nature and location of the magnetic energy source responsible for such impulsive heating is poorly understood. Using observations of seven active regions from the Solar Dynamics Observatory, we found that a majority of coronal loops hosting hot plasma have at least one footpoint rooted in regions of interacting mixed magnetic polarity at the solar surface. In cases when co-temporal observations from the Interface Region Imaging Spectrograph space mission are available, we found spectroscopic evidence for magnetic reconnection at the base of the hot coronal loops. Our analysis suggests that interactions of magnetic patches of opposite polarity at the solar surface and the associated energy release during reconnection are key to impulsive coronal heating.

Propagating brightenings in small loop-like structures in the quiet-Sun corona: Observations from Solar Orbiter/EUI

“…The light curves from the two opposite ends of the loop, that is, from B1 and B3, show rising trends well before the propagating brightenings from B2 actually reached them. This suggests the following scenario: although the main reconnection takes place near the apparent loop apex, the footpoints become excited simultaneously, which is similar to the near-simultaneous footpoint brightenings observed in active region core loops (see Chitta et al 2020). It is also possible, however, that (undetected) fainter propagating brightenings from L16, page 3 of 8 B2 have excited the footpoints B1 and B3.…”

“…Because they are nearly ubiquitous, these brightenings were initially thought to be potential candidates for coronal heating (Hudson 1991). However, further investigations indicate that significantly more (∼100 times) of these events would be required in order to account for the necessary energy budget (Aschwanden et al 2000b;Chitta et al 2021a). White boxes outline the locations of the six events studied here.…”

“…On the other hand, analyzing Hi-C data, Winebarger et al (2013) reported localized plasma flows at high speeds (between 90-290 km s −1 ) within small loops that are embedded inside a moss region. Recently, a statistical study of EUV bursts in quiet-Sun regions has been presented in Chitta et al (2021a). The detection of these burst-like features was primarily constrained by the coarser spatial resolution of the AIA data (about 900 km) used in that study.…”

Three-dimensional magnetic reconnection in astrophysical plasmas

“…For observed parameter values, the energy release is sufficient to heat the chromosphere and corona and can account for a range of observed dynamic effects. More recently, the model has been supported and extended by an analysis of reconnection at a 3D separator current sheet [67], as well as by numerical simulations [131] and observations of heating in the core of ARs in bright loops with flux cancellation at their footpoints [132].…”

Formation of solar coronal loops through magnetic reconnection in an emerging active region

“…Chen et al (2014) presented a model for the formation of coronal loops in an emerging AR, where the loop formation is triggered by an increase in the upward-directed Poynting flux at the loop footpoints as a result of the advection of the photospheric magnetic field. The relationship between impulsive coronal heating in ARs and magnetic field evolution at the solar sur-face was investigated by Chitta et al (2018) and Chitta et al (2020). They found that the energy released through interactions between the opposite magnetic polarities in the photosphere could be responsible for the coronal emission in the cores of ARs.…”