Spatial and temporal variations of solar coronal loops

Skylab EUV observations of an active region near the solar limb with both hot and cool loops present were analyzed. The observed intensity variations for hot loops were small, typically a few percent over a period of 30 min. The cool loops exhibited stronger variations, sometimes appearing and disappearing in 5 to 10 min. Most of the cool material observed in the loops appeared to be caused by the downward flow of coronal rain and by the upward ejection of chromospheric material in surges. The frequent EUV brightenings observed near the loop footpoints appear to have been produced by both in situ transient energy releases and the infall/impact of coronal rain. The mean energy input required to balance the radiative and conductive cooling of the hot loops is approximately 0.003 erg/cu cm/s.