Subflares and surges in AR 2744 during the Solar Maximum Mission

Active region NOAA 2744, which was at S25, had its central meridian passage on Oct 23 1980 and was relatively quiet according to H alpha, UV and X-ray observations made by the Solar Maximum Mission (SMM), The region was also observed by the Marshall Space Flight Center (MSFC) vector magnetograph. During its disk passage only subflares and surges were detected. Their locations appeared to be governed by the magnetic topology. On October 21 a miniflare occurred close to the separator between the two main sunspots. On October 22 the emergence of a small region of parasitic polarity in the existing magnetic field appeared to be responsible for three subflares and subsequent surges. We discuss the energy budget for plasmas at temperatures in the 10(4) K, 10(5) K and 10(6) K ranges in the context of surge-trigger mechanisms. On October 21 the energy deposition driving the surges did not produce a high temperature plasma. By October 22 the active region had evolved and the surges were now associated with some high temperature plasma. However, the energy radiated at transition region temperatures would be larger than that estimated in X-rays depending on the dilution factor. This would imply a continuous influx of energy in order to sustain the long duration surge (30 min) rather than a simple, impulsive energy input. If the electron density in the 10(4)-10(5) K plasma is taken as similar to 10(12) cm(-3) the diameter of individual surge loops should only be similar to 40 km. The relevance of our results to (a) reconnection and (b) gradient pressure driven models for surges is discussed.