Velocity Fields in the Solar Corona during Mass Ejections as observed with UVCS–[ITAL]SOHO[/ITAL]

Abstract

This Letter presents the observations of the first two coronal mass ejections (CMEs) obtained with the Ultraviolet Coronagraph Spectrometer of SOHO. Both CMEs were observed at high spectral resolution in the ultraviolet domain. The first event on 1996 June 6-7 was observed in H I Lyα λ1216 and Lyβ λ1026, O VI λλ1032 and 1037, Si XII λλ499 and 521 and imaged within 1.5 and 5 R☉. The second event on 1996 December 23 was observed in several H I lines and cool lines such as C III λ977, N III λλ990-992, and O V λ630. The analysis of line profiles has allowed us to determine the line-of-sight velocities of the extended corona during a mass ejection. In particular there is evidence for mass motions consistent with untwisting magnetic fields around an erupted flux tube in one of the events and line of sight velocities of 200 km s-1 in the early phase of the second event presumably related to the expansion of the leading arch of the transient.