Implications of the abundance of halo coronal mass ejections for the strength of solar cycle 25

TL;DR

This study compares halo CME activity across solar cycles 23, 24, and 25, finding similarities between cycles 24 and 25, suggesting that solar cycle 25 is likely similar or slightly stronger than cycle 24.

Contribution

It provides the first comparative analysis of halo CME abundance and properties across three consecutive solar cycles, informing predictions of cycle 25's strength.

Findings

Halo CME abundance is similar in cycles 24 and 25.

Weaker cycles show increased halo CME expansion due to lower heliospheric pressure.

Cycle 25 is predicted to be similar or slightly stronger than cycle 24.

Abstract

We assess the relative strength of solar cycle (SC) 25 with respect to SCs 23 and 24 based on the abundance of halo coronal mass ejections (CMEs). We make use of the halo CME database (https://cdaw.gsfc.nasa.gov/CME_list/halo/halo.html) to compare the halo CME abundance during the first four years in each of SCs 23 to 25. The main result is that in several aspects such as the abundance, occurrence rate, source locations, and halo heights, halo CMEs are similar between SCs 24 and 25 but different from SC 23. This result follows from the fact that weaker cycles have low heliospheric total pressure, whose backreaction on CMEs allows them to expand more and hence enhancing the chance of becoming a halo. The solar cycle variation of halo CME properties is consistent with the precursor-based cycle prediction methods that indicate SC 25 is similar to or only slightly stronger than SC 24.