Plasma ejections and shock waves in the solar atmosphere

Recent space observations have revealed that the solar atmosphere is much more dynamic than had been thought and is full of plasma ejections and shock waves. It is interesting to note that as observational accuracy becomes better and better, more and more tiny jets, shocks, and small flares (microflares and nanoflares) have been found. It is also interesting to note that the structure and dynamics of these tiny phenomena are often similar to those of larger phenomena. This led us to develop a unified model that explains both large-scale and small-scale eruptions observed in the solar atmosphere, in which magnetic reconnection plays a key role. In this paper, we review plasma ejections and shock waves observed in the solar atmosphere and discuss how these dynamic phenomena have been studied using magnetohydrodynamic (MHD) simulations. We also report recent solar observational projects in Japan; one of them is a space mission called Hinode (previously called Solar-B) of JAXA/ISAS with US/UK/ESA collaboration, and the other is the solar magnetic activity research telescope (SMART) built at Hida Observatory of Kyoto University.