Transequatorial magnetic flux loops on the Sun as a possible new source of geomagnetic storms

Abstract

Some intense geomagnetic storms have no clear solar activity several days prior to their onset (SSC). On the other hand, some of such storms are associated with an unmistakable indication of magnetic flux ropes in interplanetary space. We found that some of such SSC geomagnetic storms occurred several days after the passage of transequatorial loops on the central part of the solar disk; transequatorial magnetic loops connect sunspot groups between the northern and southern hemispheres and at times show some brightening activity for a day or so. Since transequatorial loops must have the IMF Bz component, we examined them as a new possible source of geomagnetic storms, in addition to solar flares and filament disappearances.