Statistics of quiet Sun extreme ultraviolet intensities

The frequency distribution of the extreme ultraviolet (EW) emission line in tensities in the quiet Sun has in the past often been modelled using two Ga ussians. This gives adequate fits to observed distributions of average stat istical significance. In this paper we test this and other distribution fun ctions against observed distributions with exceptional statistical signific ance. The data were obtained in a number of spectral lines observed with tw o extreme ultraviolet spectrometers on board the Solar and Heliospheric Obs ervatory (SOHO). In this way, the influence of spatial resolution and other instrument-specific parameters can be identified. The observations span a period of more than two years and provide a very large data set of radiance measurements of the quiet Sun at or near solar disk centre. We show that t he frequency distribution of the radiance is best modelled by a lognormal d istribution. The fact that the radiance distribution of the quiet Sun inclu ding the network and the intranetwork is better reproduced by a single logn ormal distribution function than by two Gaussians suggests that the same he ating processes are acting in both types of features. The parameters of the lognormal fit show a clear temperature dependence, wi th the transition region lines exhibiting the largest skewness of the distr ibution and the chromospheric intensity distributions being the most symmet ric.