Solar Wind Helium Abundance Heralds the Onset of Solar Cycle 25

Abstract:

We study the solar wind helium-to-hydrogen abundance's (A_he) relationship to solar cycle onset. We identify a rapid depletion and recovery in A_he immediately prior to sunspot number (SSN) minima. This depletion happens at approximately the same time across solar wind speeds, implying that it is formed by a mechanism distinct from the one that drives A_he's solar cycle scale variation and speed-dependent phase offset with respect to SSN. As A_he's rapid depletion and recovery have already occurred and A_he is now increasing as it has following previous solar minima, we infer that solar cycle 25 has already begun.