X-RAY CORONAL CHANGES DURING HALO CMES

Using the Yohkoh soft X-ray images, we examine the coronal structures associated with ''halo'' coronal mass ejections (CMEs). These may corr espond to events near solar disk center. Starting with a list of eleve n confirmed halo CMEs over the time range from December 1996 through M ay 1997 we find seven with surface features identifiable in soft X-ray s, with GOES classifications ranging from A1 to M1.3. These have a cha racteristic pattern of sigmoid --> arcade development. In each of thes e events, the pre-flare structure disrupted during the flare, leaving the appearance of compact transient coronal holes. The four remaining events had weak or indistinguishable signatures in the X-ray images. F or the events for which we could see well-defined coronal changes, we confirm our previous result that the estimated mass loss inferred from the soft X-ray dimming is a small fraction of typical CME masses [Ste rling & Hudson 1997].