SOHO EIT observations of extreme-ultraviolet "dimming" associated with a halo coronal mass ejection

A solar flare was observed on 1997 April 7 with the Soft X-ray Telescope (S XT) on Yohkoh. The flare was associated with a "halo" coronal mass ejection (CME). The flaring region showed areas of reduced soft X-ray (SXR) brightn ess-"dimmings"-that developed prior to the CME observed in white Light and persisted for several hours following the CME. The most prominent dimming r egions were located near the ends of a preflare SXR S-shaped (sigmoid) feat ure that disappeared during the event, leaving behind a postflare SXR arcad e and cusp structure. Based upon these and similar soft X-ray observations, it has been postulated that SXR dimming regions are the coronal signatures (i.e., remnants) of magnetic flux ropes ejected during CMEs. This Letter r eports new observations of coronal dimming at extreme-ultraviolet (EUV) wav elengths obtained with the Extreme-ultraviolet Imaging Telescope (EIT) on t he Solar and Heliospheric Observatory (SOHO). A series of EIT observations in the 195 Angstrom Fe XII wavelength band were obtained simultaneously wit h SXT during the 1997 April 7 flare/CME. The EIT observations show that reg ions of reduced EW intensity developed at the same locations and at the sam e time as SXR dimming features. The decrease in EW intensity (averaged over each dimming region) occurred simultaneously with an increase in EUV emiss ion from flaring loops in the active region. We interpret these joint obser vations within the framework of flux-rope eruption as the cause of EUV and SXR coronal dimmings, and as the source of at least part of the CME.