CORONAL RADIO-BURSTS - A SIGNATURE OF NANOFLARES

Coronal heating may be a result of frequent microscopic energy release s, which Parker has termed ''nanoflares.'' Since solar radio type I bu rsts, which are frequently observed at meter wavelengths, involve extr emely small amount of energy, we have determined the frequency distrib ution of the peak flux density of these bursts. The study has been per formed on 11 noise storm events observed by the Nancay Radioheliograph at 164, 237, and 327 MHz. At each frequency, and for the 11 noise sto rms, the peak flux density distribution of type I bursts can be well r epresented by a power law. The index ct of the distribution, similar t o 3, is nearly independent of the observing frequency and does not var y much from one noise storm to the other, i.e., from one active region to the other. This index is significantly steeper than that measured for various other flare phenomena (<2). There are noise storm theories and various spectral and imaging radio observations that suggest that type I bursts may be a nonthermal signature of energy release fragmen ts. If this is the case, such a steep power-law distribution is consis tent with the prediction of ''avalanche'' models developed for small e nergy release events reminiscent of nanoflares, as well as the idea th at small energy release events may contribute to the heating of an act ive coronal region.