A decade of solar Type III radio bursts observed by the Nancay Radioheliograph 1998-2008

Abstract

We present a statistical survey of almost 10 000 radio Type III bursts observed by the Nancay Radioheliograph from 1998 to 2008, covering nearly a full solar cycle. In particular, sources sizes, positions, and fluxes were examined. We find an east-west asymmetry in source positions which could be attributed to a 6(+/-)1 degree eastward tilt of the magnetic field, that source FWHM sizes s roughly follow a solar-cycle averaged distribution dN/ds = 14 {\nu}^{-3.3} s^{-4} arcmin^{-1} day^{-1}, and that source fluxes closely follow a solar-cycle averaged dN/dS_{\nu} = 0.34 {\nu}^{-2.9} S_{\nu}^{-1.7} sfu^{-1} day^{-1} distribution (when {\nu} is in GHz, s in arcmin, and S_{\nu} in sfu). Fitting a barometric density profile yields a temperature of 0.6 MK, while a solar wind-like (\propto h^{-2}) density profile yields a density of 1.2x10^6 cm^{-3} at an altitude of 1 RS, assuming harmonic emission. Finally, we found that the solar-cycle averaged radiated Type III energy could be similar in magnitude to that radiated by nanoflares via non-thermal bremsstrahlung processes, and we hint at the possibility that escaping electron beams might carry as much energy away from the corona as is introduced into it by accelerated nanoflare electrons.