The Backreaction of the Reduced Heliospheric Pressure on CMEs and Its Implications for the Strength of Solar Cycle 25

We investigated the abundance of halo coronal mass ejections (CMEs), solar flares, and solar wind conditions that occurred during the first 49 months of solar cycles 23-25.We find that the halo CME abundance has an inverse relation with the solar cycle strength.The reduced heliospheric total pressure, whose backreaction on CMEs allows them to expand more, resulted in the higher halo CME abundance in the weaker cycle 24.This trend continues in cycle 25, indicating that this cycle is also weak.Related effects in weaker cycles are the wider longitudinal distribution of halo CME sources and the halo formation closer to the Sun at lower CME speeds.The size of soft X-ray flares is similar and the flare abundance is not significantly different in the three cycles, indicating that the weakened state of the heliosphere affects CMEs, but not flares.These results imply that cycle 25 is weaker than cycle 23 but similar in strength to cycle 24.