Explosive events in the solar atmosphere

Two examples of explosive events observed with SUMER in transition region spectral lines are reported here; one detected in C iv 1548 Å, in a region within the northern polar coronal hole, and the other in O vi 1032 Å, in an active region. The event measured in C iv lasted ∼ 3 min and extended approximately a region of 8 arc sec along the slit (N-S) and 8 arc sec in the E-W direction. Velocities reached around 150 km s−1 in the blue wing and 100 km s−1 in the red wing. The active region events were more energetic and in total lasted ∼ 6 min. At the point of maximum activity, a region of 8 arc sec along the slit is covered by one explosive event located in the northern section of the observed region, while in the southern section we observe two events very closely located and extended over a maximum of 14 arc sec along the slit. More precisely, in the northern section we have at least two consecutive events occurring in a short time interval (∼ 12 min) separated by ∼ 3 arc sec. In the EW direction the raster length covered by each of these events was approximately 4 arc sec. The explosive events seen in O vi showed a very complex structure of subsonic and supersonic velocity flows, both red-shifted and blue-shifted. The apparent maximum velocity reached in the blue wing was approximately 250 km s−1 and 215 km s−1 in the red wing.