Correlation between sunspot number (Rz) and shock events during the solar cycle 24.

Abstract

The correlation between Rz and shock events is investigated using the temporal profiles of Rz and Aa geomagnetic index. By evaluating the activity of shock events according to the classification of Legrand et Simon (1989) and Zerbo et al. (2012), the study revealed a very low correlation between shock events and Rz. A consideration of coronal mass ejections (CMEs) data isolated fourteen (14) cases of sudden storm commencement (SSC) that were not caused by CMEs. The elimination of these cases resulted in a good correlation between Rz and magnetic cloud activity and between Rz and shock events. The correlation coefficient between Rz and shock activity has changed but remains low. That between shock events is constant. These results, clearly below those of Zerbo et al. (2012) for cycles 11 to 23, could be explained by the low agitation of shock events during cycle 24.