THE CONNECTION BETWEEN CORONAL BRIGHT POINTS AND THE VARIABILITY OF THE QUIET-SUN EXTREME-ULTRAVIOLET EMISSION

We determine the characteristics of the significant variable EUV emission from the quiet Sun by analyzing the EUV/Skylab data recorded at six wavelengths simultaneously scanning the chromosphere to the corona, from a coronal hole and a quiet region. We adopt the criterion that changes in the intensity of emission in consecutive spectroheliograms, 5.5 minute apart, are significant if larger than sigma (where sigma is the root mean square deviation from the mean in a source free region). We find that, in both regions studied, the significant variable emission is preferentially localized in EUV bright points which form the enhanced EUV emission from the quiet Sun. The spatial density of the enhanced and variable emission has a marked temperature dependence. We interpret the minimum at 3 x 10(5) K as evidence for two favored temperature distributions of closed magnetic field structures in the quiet Sun, one below 3 x 10(5) K and one at coronal temperatures, implying that not all structures in the quiet Sun necessarily reach coronal temperatures. The enhanced emission occupies between 10% and 25% of the solar surface, depending on the temperature, while the variable emission covers a smaller fraction, between 5% and 15% of the solar surface. These estimates are likely to vary with the solar cycle, since the number of bright points is known to be solar cycle dependent. The spatial density of the variable emission derived in this study represents the spatial density of random fluctuations and is an upper limit if the actual spatial scale of the variability is less than the 5" spatial resolution of the data. The radiative energy losses associated with the variable emission are a significant fraction (about 40%) of the corresponding losses from the enhanced emission. These losses, which provide a lower limit to the energy input into the variable and enhanced emission, are much smaller than the heating budget requirements of the quiet Sun.