Explosive events in the solar atmosphere seen in extreme-ultraviolet emission lines

¹ Instituto Nacional de Astrofisica, Optica y Electrónica, Puebla, Mexico e-mail: mend@inaoep.mx
² Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany

Received: 15 May 2004
Accepted: 5 October 2004

Abstract

We present observations of explosive events (EEs) in the solar atmosphere obtained with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) in the wavelength range from about 750 Å to 790 Å. Prominent spectral lines in this range are emitted by ions which have temperatures of maximum ionic abundances between ⁵ K and  K in ionization equilibrium, and are therefore expected to be formed in the transition region (TR) and in the low corona. The aim of this work is to investigate whether the EEs originate in a limited range of temperatures or in a wide interval. We analyzed the behaviour of several emission lines during 114 EEs. In many events, the radiance increased first in lines with formation temperatures near ⁵ K. A number of events produced profiles that clearly revealed blue and red components, in addition to the central line. In general, both the radiance and the line-of-sight (LOS) velocity of the blue component are larger than those of the red one. From an inspection of the profiles that did not show all three spectral components, we found, in all the cases, that the lowest temperature line showed a red shift whereas the highest temperature was characterized by a blue shift. The inverse situation was not observed. We interpret these results as an indication that most of the EEs originate at intermediate temperatures of the TR as fast reconnection jets.