PROPERTIES OF THE QUIET SUN EUV NETWORK

Observations of the quiet Sun network in a small region at Sun centre taken with the Coronal Diagnostic Spectrometer (CDS) on board SOHO are reported for EUV lines with T-e between similar to 10(4) and 10(6) K. The changing structure of the network in the upper chromosphere, tran sition region, up to the corona was examined using intensity distribut ions which were decomposed into two normal components using a mixture- modelling technique. This enabled areas of high and low intensities to be separated, and hence averaged network properties including area, i ntensity, contrast, and fractal dimension to be derived as a function of ion temperature. The network area and emission were found to be mor e concentrated in the transition region than in the chromosphere and i n the corona, although the results for the chromospheric He lines appe ar to be affected by resonance scattering. At similar to 106 K, the ar ea and emission of bright structures dramatically increase, partly due to the appearance of small coronal loops. There is also a discrete ch ange in the fractal dimension at coronal temperatures, signifying a ch ange from network to simpler coronal structures. Furthermore, the cont rast of bright to dark regions is at a maximum for T-e similar to 2.5 x 10(5) K and falls to its lowest values for coronal temperatures. The properties of several individual network structures were found to fol low the same general behaviour as in the statistical analysis. Our res ults including physical dimensions are broadly consistent with the tra nsition region model of Gabriel, although we cannot exclude the existe nce of low-lying loops as in the model of Dowdy et al.