Nanoflare
Damping quickly converts energy into heat, which is conducted by free electrons along the magnetic field lines closest to the place where the nanoflare switches on.
[5] As of 2012, then-current instruments, such as the Extreme-Ultraviolet Imaging Spectrometer on board Hinode, were not adequately sensitive to the range in which this faint emission occurs, making a confident detection impossible.
Telescopic observations suggest that the solar magnetic field, which theoretically is "frozen" into the gas of the plasma in the photosphere, expands into roughly semicircular structures in the corona.
These coronal loops, which can be seen in the EUV and X-ray images (see the figure on the left), often confine very hot plasmas, with emissions characteristic of temperature of a one to a few million degrees.
These nanoflares might themselves resemble very tiny flares, close one to each other, both in time and in space, effectively heating the corona and underlying many of the phenomena of solar magnetic activity.
Episodic heating often observed in active regions, including major events such as flares and coronal mass ejections could be provoked by cascade effects, similar to those described by the mathematical theories of catastrophes.
One of the experimental results often cited in supporting the nanoflare theory is the fact that the distribution of the number of flares observed in the hard X-rays is a function of their energy, following a power law with negative spectral index.
[13] The radiation is not the only mechanism of energy loss in the corona: since the plasma is highly ionized and the magnetic field is well organized, the thermal conduction is a competitive process.
In other words, the transition region is so steep (the temperature increases from 10 kK to 1 MK in a distance of the order of 100 km) because the thermal conduction from the superior hotter atmosphere must balance the high radiative losses, as indicated to the numerous emission lines, which are formed from ionized atoms (oxygen, carbon, iron and so on).
The Alfvén waves generated by convective motions in the photosphere can go through the chromosphere and transition region, carrying an energy flux comparable to that required to sustain the corona.
The theory initially developed by Parker of micro-nanoflares is one of those explaining the heating of the corona as the dissipation of electric currents generated by a spontaneous relaxation of the magnetic field towards a configuration of lower energy.
However this heating mechanism is not very efficient in large current sheets, while more energy is released in turbulent regimes when nanoflares happen at much smaller scale-lengths, where non-linear effects are not negligible.
