CORONAL HEATING BY NANOFLARES - INDIVIDUAL EVENTS AND GLOBAL ENERGETICS

Various mechanisms have been proposed to heat the solar corona, but none have been completely successful in accounting for its observed characteristics. Recently a further candidate has been advanced; namely, stochastic heating via a large number of tiny impulsive energy-release events, the so-called nanoflares. In this paper we develop a simple semianalytical model to describe the temporal evolution of the nanoflare plasma and to determine the response of magnetic flux tubes of different sizes to typical nanoflare energy releases. This allows us to show how the repeated occurrence of low-energy events in an originally cool loop may eventually build up a high-temperature plasma- a nanoflare-heated corona. We also calculate the average nanoflare rate of occurrence, as a function of loop size, required to keep the plasma at coronal temperatures. The collective effect of this minievent population is shown to account for the observed coronal temperature and global emission measure. The present estimates may be used as guidelines for defining the requisites of future experiments aimed at observationally testing the nanoflare heating hypothesis.