The EUV chromospheric network in the quiet Sun

Abstract

Investigations on the structure and intensity of the chromospheric network from quiet solar regions have been carried out with EUV data obtained from the Harvard spectroheliometer on the Apollo Telescope Mount of Skylab. The distribution of intensities within supergranulation cell interiors follows a near normal function, where the standard deviation exceeds the value expected from the counting rate, which indicates fine-scale structure below the 5 arc sec resolution of the data. The intensities from the centers of supergranulation cells appear to be the same in both quiet regions and coronal holes, although the network is significantly different in the two types of regions. The average halfwidth of the network elements was measured as 10 arc sec, and was independent of the temperature of formation of the observing line for 3.8 < log T e < 5.8. The contrast between the network and the centers of cells is greatest for lines with log T e ≈ 5.2, where the network contributes approximately 75% of the intensity of quiet solar regions. The contrast and fractional intensity contributions decrease to higher and lower temperatures characteristic of the corona and chromosphere.