The State of the Heliosphere Revealed by Limb Halo Coronal Mass Ejections in Solar Cycles 23 and 24

Abstract

We compare the properties of halo coronal mass ejections (CMEs) that originate close to the limb (within a central meridian distance range of 60 to 90 deg) during solar cycles 23 and 24 to quantify the effect of the heliospheric state on CME properties. There are 44 and 38 limb halos in the cycles 23 and 24, respectively. Normalized to the cycle-averaged total sunspot number, there are 42 percent more limb halos in cycle 24. Although the limb halos as a population is very fast (average speed 1464 km s-1), cycle-24 halos are slower by 26 percent than the cycle-23 halos. We introduce a new parameter, the heliocentric distance of the CME leading edge at the time a CME becomes a full halo; this height is significantly shorter in cycle 24 (by 20 percent) and has a lower cutoff at 6 Rs. These results show that cycle-24 CMEs become halos sooner and at a lower speed than the cycle-23 ones. On the other hand, the flare sizes are very similar in the two cycles, ruling out the possibility of eruption characteristics contributing to the differing CME properties. In summary, this study reveals the effect of the reduced total pressure in the heliosphere that allows cycle-24 CMEs expand more and become halos sooner than in cycle 23. Our findings have important implications for the space-weather consequences of CMEs in cycle 25 (predicted to be similar to cycle 24) and for understanding the disparity in halo counts reported by automatic and manual catalogs.

13 pages, 4 figures, one table, accepted for publication in Astrophys. J Lett. on June 10, 2020

References in corpus (5)

• Anomalous Expansion of Coronal Mass Ejections during Solar Cycle 24 and its Space Weather Implications
• Major Solar Eruptions and High Energy Particle Events during Solar Cycle 24
• The Peculiar Behavior of Halo Coronal Mass Ejections in Solar Cycle 24
• Large Solar Energetic Particle Events Associated with Filament Eruptions Outside of Active Regions
• Many-body forces in the equation of state of hyperonic matter

Cited by in corpus (7)

• Collection, Collation, and Comparison of 3D Coronal CME Reconstructions
• What do halo CMEs tell us about solar cycle 25?
• Effect of the Weakened Heliosphere in Solar Cycle 24 on the Properties of Coronal Mass Ejections
• Solar Activity and Space Weather
• Kinematic study of radio-loud CMEs associated with solar flares and DH type II radio emissions during solar cycles 23 and 24
• Drop of solar wind at the end of the 20th century
• Characteristics and evolution of sheath and leading edge structures of interplanetary coronal mass ejections in the inner heliosphere based on Helios and Parker Solar Probe observations