SOLARNET Conference: The Many Scales of the Magnetic Sun

On May 30, 2020, the Solar Orbiter High-Resolution Imager operating in 174 A being for the first time approximately at a half AU to the Sun, registered a large number of short, small-scale heating events, often called campfires, with rich morphology and smaller space-time characteristics than nanoflares. We estimate the thermal energy of the heating events from increases in the emission measure and temperature using methods assessing thermal energy in flares. We compare these with the characteristics of X-ray flares, in particular, those recorded by the X-ray spectrometer/telescope onboard Solar Orbiter. We found campfires emit thermal energy in picoflares range. The additional previously unaccounted energy input of is about 1% to the total required to sustain quiet solar corona power. The observed frequency distribution would have to continue to the femtoflares range to fulfill the observed heating requirement. We explain the existence of solar flares below the expected nanoflare threshold as follows. They originate in small coronal loops of 200-5000 km, smaller than considered by Parker. Some picoflares show only a partial energy release along a single loop.