The east-west asymmetry in Coronal Mass Ejections: evidence for active longitudes

Abstract. Various manifestations of solar activity are not uniformly distributed with heliographic longitude. By using east-west asymmetry in the occurrence rate of CMEs (coronal mass ejections), the longitudinal dependence in SOHO LASCO 1996-2004 data has been studied in this work. The solar rotation periodicity has been found, indicating the presence of active longitudes, whose phase is reversed twice during the studied period. It is more prominent in the Southern Hemisphere. The east-west asymmetry is also present when calculated for longer time periods. Sometimes (particularly during low solar activity), there is an alternation of the eastern and western domination every six months. Taking into account the orbital revolution of the Earth about the Sun, this indicates the existence of enhanced activity, fixed in space (not undergoing Carrington rotation). Moreover, there is about a 3.7% overall excess of western events, lasting for the entire reported time, suggesting some bias in the observations. A hypothesis to explain this phenomenon is proposed.