MAGNETIC STRUCTURES OF SOLAR ACTIVE REGIONS, FULL-HALO CORONAL MASS EJECTIONS, AND GEOMAGNETIC STORMS

We have analyzed three active regions to investigate the relationship between magnetic configurations of active regions and geomagnetic storms. Each active region was associated with multiple full-halo coronal mass ejections (CMEs). This study demonstrates that, although full-halo CMEs may originate from the same active region, it is not necessary for them to have similar geoeffectiveness, depending on the magnetic configurations actually involved in the corresponding flare activities. This implies that (1) the flares, CMEs, and geomagnetic storms are closely related magnetically, as already suggested by many others, and (2) the occurrence of solar active regionYrelated geomagnetic storms may be determined by the magnetic fields that are involved in the corresponding solar flares. These associ-ations suggest ways to improve geomagnetic storm prediction. Subject headinggs: Sun: activity — Sun: coronal mass ejections (CMEs) 1.