The Peculiar Behavior of Halo Coronal Mass Ejections in Solar Cycle 24

Abstract

We report on a remarkable finding that the halo coronal mass ejections (CMEs) in cycle 24 are more abundant than in cycle 23, although the sunspot number in cycle 24 has dropped by about 40%. We also find that the distribution of halo-CME source locations is different in cycle 24: the longitude distribution of halos is much flatter with the number of halos originating at central meridian distance >/=60 degrees twice as large as that in cycle 23. On the other hand, the average speed and the associated soft X-ray flare size are the same in the two cycles, suggesting that the ambient medium into which the CMEs are ejected is significantly different. We suggest that both the higher abundance and larger central meridian longitudes of halo CMEs can be explained as a consequence of the diminished total pressure in the heliosphere in cycle 24 (Gopalswamy et al. 2014). The reduced total pressure allows CMEs expand more than usual making them appear as halos.

12 pages, 5 figures, accepted for publication in the Astrophysical Journal Letters, April 7, 2015

References in corpus (3)

• Anomalous Expansion of Coronal Mass Ejections during Solar Cycle 24 and its Space Weather Implications
• Spatial Relationship between Solar Flares and Coronal Mass Ejections
• Width of Radio-Loud and Radio-Quiet CMEs

Cited by in corpus (5)

• A Statistical Study of CME Properties and of the Correlation Between Flares and CMEs over Solar Cycles 23 and 24
• The 2012 July 23 Backside Eruption: An Extreme Energetic Particle Event?
• Importance of CME Radial Expansion on the Ability of Slow CMEs to Drive Shocks
• Mass Loss via Solar Wind and Coronal Mass Ejections During Solar Cycle 23 and 24
• Active Longitude and Coronal Mass Ejection Occurrences