An Hα surge provoked by moving magnetic features near an emerging flux region

We present a detailed study of Hα surges from cotemporal high-resolution multiwavelength images of NOAA AR 8227 obtained by the 50 cm Swedish Vacuum Solar Telescope (formerly situated on La Palma, Spain) and TRACE. We find that two kinds of collisions between opposite polarity magnetic flux produce the surges. First, one edge of an emerging flux region (EFR) collides with the preexisting magnetic field and causes continual surge activities, which have already been named EFR surges by previous authors. Secondly, moving magnetic features (MMFs), which emerge near the sunspot penumbra, pass through the ambient plasma and eventually collide with the opposite polarity magnetic field of the EFR. During their passage from the sunspot penumbra to the EFR, the MMFs constantly interacted with other magnetic elements and had a close relationship and showed similar flow patterns to Ca II K bright points. These brightenings were located at the leading edges of the MMFs. Cancellation of opposite polarity magnetic flux at the surge footpoint is observed, accompanied by chromospheric and coronal brightenings. We explain the evolutionary and morphological characteristics of the multiwavelength features associated with the Hα surges in both cases by the extension of previous 2D schematic models of reconnection in surges. Furthermore, by measuring the expansion velocity and photospheric magnetic field around the surge footpoint, we estimate a dimensionless reconnection rate of 0.04 (ratio of inflow velocity to Alfvén velocity). This is sufficient to produce a significant surge that heats the chromospheric plasma to coronal temperatures.