Below the loops, there is a void. Yohkoh has seen many arcade events such as this one. We speculate that this is because of magnetic pressure internal to the cavity. The cylindrical configuration points to the existence of a separate domain in the form of a flux rope. This subject is fraught with confusion.
Many flares show precursors of the type seen above, i.e. a slow rise prior to the impulsive phase.
Many other flares don't. They found 8 out of 32 cases in which a pre-flare loop arguably could be seen prior to the flare itself. In the example above we have an exceptionally clear case of this. One can trace an apparently continuous development of flare brightening, following the precursor seen above, into the flare state itself.