Far‐Ultraviolet Spectra of Fast Coronal Mass Ejections Associated with X‐Class Flares

Abstract

The Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory satellite has observed very fast coronal mass ejections (CMEs) associated with X-class flares. These events show spectral signatures different from those seen in most other CMEs in terms of very rapid disruption of the pre-CME streamer, very high Doppler shifts, and high-temperature plasma visible in the [Fe XVIII] emission line. This paper describes three very similar events on 2002 April 21, July 23, and August 24 associated with X-class flares. We determine the physical parameters of the pre-CME streamers and discuss the geometric and physical nature of the streamer blowouts. In the April 21 event, the hot plasma seen as [Fe XVIII] is not related to the structure seen in [Fe XXI] by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) instrument at lower heights. It has the form of a rapidly expanding fan, quite likely a current sheet. In the August event, on the other hand, the [Fe XVIII] is probably a bubble of hot plasma formed by reconnection in the wake of the CME. C III emission from the July 23 flare is detected as stray light in the UVCS aperture. It precedes the hard X-ray brightening by about 2 minutes.