What do halo CMEs tell us about solar cycle 25?

TL;DR

This study analyzes halo CMEs during solar cycles 23-25 to infer that solar cycle 25 is likely similar to or slightly stronger than cycle 24, based on CME and solar wind properties.

Contribution

It provides a comparative analysis of halo CME occurrence rates and solar wind parameters across three solar cycles to predict the strength of cycle 25.

Findings

HCME occurrence rate normalized to sunspots is higher in cycles 24 and 25 than in 23.

Solar wind pressure in cycle 25 is ~35% lower than in cycle 23.

Solar energetic particle events and geomagnetic storms in cycle 25 are similar to cycle 24.

Abstract

It is known that the weak state of the heliosphere due to diminished solar activity in cycle 24 back-reacted on coronal mass ejections (CMEs) to make them appear wider for a given speed. One of the consequences of the weak state of the heliosphere is that more CMEs appear as halo CMEs (HCMEs), and halos are formed at shorter heliocentric distances. Current predictions for the strength of solar cycle (SC) 25 range from half to twice the strength of SC 24. We compare the HCME occurrence rate and other properties during the rise phase of cycles 23, 24, and 25 to weigh in on the strength of SC 25. We find that HCME and solar wind properties in SC 25 are intermediate between SCs 23 and 24, but closer to SC 24. The HCME occurrence rate, normalized to the sunspot number, is higher in SCs 24 and 25 than in SC 23. The solar wind total pressure in SC 25 is ~35% smaller than that in SC 23. Furthermore, the occurrence rates of high-energy solar energetic particle events and intense geomagnetic storms are well below the corresponding values in SC 23, but similar to those in SC 24. We conclude that cycle 25 is likely to be similar to or slightly stronger than cycle 24, in agreement with polar-field precursor methods for cycle 25 prediction