CORONAL HEATING BY NANOFLARES - INDIVIDUAL EVENTS AND GLOBAL ENERGETICS

Various mechanisms have been proposed to heat the solar corona, but no ne have been completely successful in accounting for its observed char acteristics. Recently a further candidate has been advanced; namely, s tochastic heating via a large number of tiny impulsive energy-release events, the so-called nanoflares. In this paper we develop a simple se mianalytical model to describe the temporal evolution of the nanoflare plasma and to determine the response of magnetic flux tubes of differ ent sizes to typical nanoflare energy releases. This allows us to show how the repeated occurrence of low-energy events in an originally coo l loop may eventually build up a high-temperature plasma- a nanoflare- heated corona. We also calculate the average nanoflare rate of occurre nce, as a function of loop size, required to keep the plasma at corona l temperatures. The collective effect of this minievent population is shown to account for the observed coronal temperature and global emiss ion measure. The present estimates may be used as guidelines for defin ing the requisites of future experiments aimed at observationally test ing the nanoflare heating hypothesis.