Active region blinkers: Transient events in the solar atmosphere

As part of the St. Andrews/RAL Loops Campaign, the NIS instrument on CDS was used to study a small active region between 14^th and 15^th November 1996. High cadence observations over a wide range of temperatures reveal many examples of temporally well-defined, localised increases in intensity in the brightest regions. This is particularly the case for the transition region line (O V 629.73Å). Two such events are presented here that show a substantial increase in emission. It is found that these impulsive events effect the plasma temperature over two orders of magnitude (chromospheric to coronal), the event lifetimes being hundreds of seconds. The calculated Doppler velocities range from 30 to 70 km s^-1 in O V 629.73Å, comparable with blinkers. Also, there is an apparent line broadening connected with the events. The fact that the brightenings enhance the emission in coronal lines (up to 2.5 × 10⁶ K) presents the possibility that these type of transient phenomena could be observed by SXT on Yohkoh. A crude calculation of the thermal energy content suggests that these events may be indicative of low energy, discrete heating in the corona, the energy released being of the order of 10²⁴ erg.