Yohkoh/SXT soft x-ray observations of sudden mass loss from the solar corona

With soft X-ray imaging we can study the entire coronal volume, except for cold inclusions such as prominences, as a function of time. This should allow us to observe the origins of coronal mass ejections. We report here an initial survey of the Yohkoh/SXT observations at the times of reported or apparent mass ejections: three LDE flare events and two large-scale arcade formations. For each of the events we can easily detect sudden coronal dimming, which we interpret as the launch interval of a CME. In one of the flare events we have found a well-defined plasma cloud, apparently formed from a set of loop structures, which rises and disappears during the growth phase of the flare emission. Its mass amounted to some 4×1014 g with a density of 3×108 cm−3 and a temperature of 2.8 MK before its disappearance.