Solar Wind Helium Abundance Heralds Solar Cycle Onset

We study the solar wind helium-to-hydrogen abundance’s (A_He) relationship to solar cycle onset. Using OMNI/Lo data, we show that A_He increases prior to sunspot number (SSN) minima. We also identify a rapid depletion and recovery in A_He that occurs directly prior to cycle onset. This A_He shutoff happens at approximately the same time across solar wind speeds (v_sw) and the time between successive A_He shutoffs is typically on the order of the corresponding solar cycle length. In contrast to A_He’s v_sw-dependent phase lag with respect to SSN (Alterman and Kasper, 2019), A_He shutofff’s concurrence across v_sw likely implies it is independent of solar wind acceleration and driven by a mechanism near or below the photosphere. Using brightpoint (BP) measurements to provide context, we infer that A_He shutoff is likely related to the overlap of adjacent solar cycles and the equatorial flux cancelation of the older, extended solar cycle during solar minima.