Evidence for distinctive changes in the solar wind helium abundance in cycle 24

Abstract

The relative abundance of alpha particles with respect to proton, usually expressed as $A_{He}$ = ($n_{\alpha }/n_p$)*100, is known to respond to solar activity although changes in its behaviour in the last four solar cycles are not known. In this letter, by systematically analysing inter-calibrated $A_{He}$ data obtained from the first Lagrangian point of the Sun-Earth system, we show that $A_{He}$ variations are distinctively different in solar cycle 24 as compared to the last three cycles. The frequency of $A_{He}$ = 2-3% events is significantly higher in slow/intermediate solar winds in cycle 24 as opposed to the dominance of the typical $A_{He}$ = 4-5% events in the previous three cycles. Further, the occurrence of $A_{He}$ $\ge$ 10% events is significantly reduced in cycle 24. Not only that, the changes in delay of $A_{He}$ with respect to peak sunspot numbers are less sensitive to changes in solar wind velocity in cycle 24. The investigation suggests that the coronal magnetic field configuration started undergoing systematic changes starting from cycle 23 and this altered magnetic field configuration affected the way helium got processed and depleted in the solar atmosphere.

References in corpus (3)

• Predicting solar cycle 24 with a solar dynamo model
• Element Abundances: A New Diagnostic for the Solar Wind
• Helium Variation Across Two Solar Cycles Reveals A Speed-Dependent Phase Lag

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• A holistic approach to understand Helium enrichment in Interplanetary coronal mass ejections: New insights
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• The Evolution of Heavy Ion Abundances with Solar Activity
• Helium Abundance Periods Observed by the Solar Probe Cup on Parker Solar Probe: Encounters 1-14
• New insights on the behaviour of solar wind protons and alphas in the Stream Interaction Region in solar cycle 23 and 24
• On the Regulation of the Solar Wind Helium Abundance by the Hydrogen Compressibility