Extreme-ultraviolet bursts and nanoflares in the quiet-Sun transition region and corona

Abstract

The quiet solar corona consists of myriads of loop-like features, with magnetic fields originating from network and internetwork regions on the solar surface. The continuous interaction between these different magnetic patches leads to transient brightenings or bursts that might contribute to the heating of the solar atmosphere. The literature on a variety of such burst phenomena in the solar atmosphere is rich. However, it remains unclear whether such transients, which are mostly observed in the extreme ultraviolet (EUV), play a significant role in atmospheric heating. We revisit the open question of these bursts as a prelude to the new high-resolution EUV imagery expected from the recently launched Solar Orbiter. We use EUV image sequences recorded by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) to investigate statistical properties of the bursts. We detect the bursts in the 171 Å filter images of AIA in an automated way through a pixel-wise analysis by imposing different intensity thresholds. By exploiting the high cadence (12 s) of the AIA observations, we find that the distribution of lifetimes of these events peaks at about 120 s. However, a significant number of events also have lifetimes shorter than 60 s. The sizes of the detected bursts are limited by the spatial resolution, which indicates that a larger number of events might be hidden in the AIA data. We estimate that about 100 new bursts appear per second on the whole Sun. The detected bursts have nanoflare-like energies of 1024 erg per event. Based on this, we estimate that at least 100 times more events of a similar nature would be required to account for the energy that is required to heat the corona. When AIA observations are considered alone, the EUV bursts discussed here therefore play no significant role in the coronal heating of the quiet Sun. If the coronal heating of the quiet Sun is mainly bursty, then the high-resolution EUV observations from Solar Orbiter may be able to reduce the deficit in the number of EUV bursts seen with SDO/AIA at least partly by detecting more such events.

Capturing transient plasma flows and jets in the solar corona

“…Coronal bright points are widely studied features in the literature (Golub et al 1974;Madjarska 2019). The data also revealed a number of transient roundish and loop-like elongated brightenings (EUV bursts or campfires; e.g., Chitta et al 2021;Berghmans et al 2021) that are distributed throughout the field of view (not marked in Fig. 1).…”

“…Sect. 1; see also Chitta et al 2021). These transient events exhibit rapid (internal) dynamics that can be seen as intensity disturbances along the brightenings in the data analyzed here.…”

“…Because these jets are characterized by their intensity enhancement with respect to the local background, it is either the segments of these jets or the whole structures themselves that could be classified as quiet-Sun EUV bursts (Chitta et al 2021) or campfires (Berghmans et al 2021), which are likely akin to small-scale bursts detected in active regions (Tiwari et al 2019). Our spatio-temporal analysis provides further insights into the dynamics and transient nature of these small-scale events.…”

“…Chitta et al 2017;Panesar et al 2018Panesar et al , 2019. There is also some evidence for a direct association of explosive events identified in spectroscopic observations and plasma jets observed in imaging observations (Innes & Teriaca 2013;Chen et al 2019;Chitta et al 2021).…”

An Analysis of Spikes in Atmospheric Imaging Assembly (AIA) Data

“…However, a search of the literature suggests that it is relatively rare for users to respike AIA data as part of their analysis. The full text of articles in the journals Solar Physics, The Astrophysical Journal, and Astronomy & Astrophysics were searched for terms such as "respike", "re-spike", and variants thereof, and only five were found: the two articles mentioned above and the articles by Li, Innes, and Ning (2016), Alissandrakis et al (2017), and Chitta, Peter, and Young (2021). This is despite the high usage of AIA data as demonstrated by the AIA instrument article (Lemen et al, 2012) having received over 2500 citations.…”