## Helium Variation Across Two Solar Cycles Reveals A Speed-Dependent Phase Lag

28 Jun 2019  ·  Alterman B. L., Kasper Justin C. ·

We study the relationship between solar wind helium to hydrogen abundance ratio ($A_\mathrm{He}$), solar wind speed ($v_\mathrm{SW}$), and sunspot number (SSN) over solar cycles 23 and 24. This is the first full 22-year Hale cycle measured with the Wind spacecraft covering a full cycle of the solar dynamo with two polarity reversals... While previous studies have established a strong correlation between $A_\mathrm{He}$ and SSN, we show that the phase delay between $A_\mathrm{He}$ and SSN is a monotonic increasing function of $v_\mathrm{SW}$. Correcting for this lag, $A_\mathrm{He}$ returns to the same value at a given SSN over all rising and falling phases and across solar wind speeds. We infer that this speed-dependent lag is a consequence of the mechanism that depletes slow wind $A_\mathrm{He}$ from its fast wind value during solar wind formation. read more

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Space Physics Solar and Stellar Astrophysics