Relationship between X-class Flares and Geomagnetic Effects

A statistical study has been performed on all the geomagnetic storm events caused by Coronal Mass Ejections (CMEs) which are associated with flares from January 2010 to December 2012. The following results are obtained. The sources of the CMEs mentioned above are distributed mainly from 45°E to 45°W on the solar surface, accounting 78.95% of the total events, and most of them are distributed in the western hemisphere, thus the sources of CMEs located in the western hemisphere are more likely to cause geomagnetic effects. The X-class flares are more likely to be associated with geomagnetic effects, and geomagnetic storms will be observed in two or three days after the eruption of 60% of X-class flares, while the flares of other classes have a much lower probability to associate with geomagnetic effects, less than 10% for all of them. By analyzing all the X-class flares erupted during this period on the solar disk, it is found that for the X-class flares located from 45°E to 45°W in heliographic longitude, if there are no large-scale disturbances on the solar surface nor the accompanied CMEs during the eruptions, the probability of occurrence of geomagnetic storms after the flares will be very small. Therefore, a new method to forecast the geomagnetic storms by analyzing the observed solar image data has been proposed.