Collision of Plasma Flows in a Current Loop
Chromospheric evaporation is one of the important mechanisms for energy transports at the rise phase of solar flares. With its high resolution, the Yohkoh SXT has ability to detect moving evaporation fronts, provided that the instrument takes images since the very beginning of a flare. This anticipation has been proven for the first time by Hudson et al. (1993), who show that the Yohkoh SXT can observe the upward-moving fronts along loop legs as it happens. In his study of the Yohkoh HXT, Sakao (1994) found that double sources are a common feature in the footpoints of a single loop. Since the HXT emissions from the footpoints vary simultaneously, it implies that accelerated electrons stream down along the loop towards both ends. By the subsequent evaporation of the lower solar atmosphere from the ends is possible to be created. The existence of such chromospheric evaporation has been modeled as one of the four phases of a flare on the basis of synthesized SXT images (Reale and Peres 1995).