High-speed streams from coronal holes and coronal mass ejections around the solar minimum of cycle 22 Original Research Article

The soft X-ray telescope on board Yohkoh enables continuous observations of coronal holes and disturbances in the solar corona. Although there were recurrent high-speed streams emanated from the coronal holes around the solar minimum of cycle 22, their effect on geomagnetic disturbances seems to be weak during this period. A half of geomagnetic disturbances (Dst≧−50 nT) were associated with coronal mass ejections (CMEs). Several geomagnetic disturbances associated with both high-speed streams and CMEs had large magnitude and long duration.