Nanoflare heating in the quiet corona: evidence and problems Original Research Article

The content of coronal material in the quiet Sun is not constant, as soft X-ray (SXR) and high-temperature EUV line observations have shown. The observed temporal variations in SXR and EUV flux are interpreted as heating events showing many analogies to flares occurring in active regions. Compared to a large flare in an active region, the thermal energy input of a heating event in the quiet corona is 6 or more orders of magnitude smaller. Heating events in the quiet corona are therefore often called microflares or nanoflares. The total heating rate of nanoflares in the quiet corona has been investigated in several works by many different authors: Do nanoflares provide enough energy to heat the quiet corona? The results of the different studies are controversial. In this review, recent observational studies on nanoflare heating in the quiet corona and their different results are compared and discussed.