On the transition region explosive events

We describe the properties of high-velocity and explosive events in the sol ar transition region determined from time series of data taken by the Trans ition Region and Coronal Explorer and the SUMER instrument on the Solar and Heliospheric Observatory (SOHO) simultaneously in several chromospheric an d transition region lines co-aligned with high-resolution Michelson Doppler Imager (SOHO) magnetograms. We outline what the various features of these events can tell us about the heating mechanisms and formation of plasma flo ws. Our results strongly support the mechanism of hydrodynamic cumulation o f energy associated with the cascade of shock waves produced by colliding a nd reconnecting flux tubes in the photospheric network (as recently discuss ed by T. D. Tarbell et al.), We find that the majority of the explosive eve nts are caused by the explosive instability occurring in the presence of th e behind-shock downflows, and less than 10% can be explained by the direct collision of shuck fronts.