Variability of the quiet photospheric network

Abstract

High-resolution photographs of the photospheric network taken in the Caii K 3933 Å line and at λ4308 Å are analysed in order to study the variation, in latitude and over the sunspot cycle, of its density (the density is defined as the number of network elements - also called facular points - per surface unity). It appears that the density of the photospheric network is not distributed uniformly at the surface of the Sun: on September 1983, during the declining phase of the current activity cycle, it was weakened at both the low (equatorial) and high (polar) active latitudes, while it was tremendously enhanced toward the pole. The density at the equator is varying in antiphase to the sunspot number: it increases by a factor 3 or more from maximum to minimum of activity. As a quantum of magnetic flux is associated to each network element, density variations of the photospheric network express in fact variations of the quiet Sun magnetic flux. It thus results that the quiet Sun magnetic flux is not uniformly distributed in latitude and not constant over the solar cycle: it probably varies in antiphase to the flux in active regions.

The variation over the solar cycle and the latitude distribution of photospheric network density are compared to those of X-ray bright points and ephemeral active regions: there are no clear correlations between these three kinds of magnetic features.