Signatures of magnetic reconnection and observed EUV emission line profiles in an active region Original Research Article

We report on observations with SUMER on SOHO of high-velocity events, also called explosive events. The high spatial and spectral resolutions of SUMER allow simultaneous observations of EUV emission lines formed at different temperatures within the transition region. Complex line profiles with three separate line components appear to be a characteristic feature of many high-velocity events based on a survey of Si IV λ1393 observations. The present study is based on 551 spectra of the active region NOAA 7995 obtained on 17 November 1996. We find that the complex line profiles of explosive events may be represented by a composite line profile consisting of three Gaussian line components. Both positive and negative line-of-sight velocities are found to be significantly larger at 6.3 ×105 K than at 1.5 – 1.7 ×105 K. We briefly confront the observations with signatures predicted from magnetic reconnections, disturbances originating in the corona and flows in an extremely structured transition region.