Preprint
Evidence for Solar-Cycle Modulation of the Alpha-to-Proton Temperature Ratio in Solar Wind
arXiv
arXiv
08/11/2026
DOI: 10.48550/arxiv.2608.10819
Abstract
The influence of collisional age(A_(c))on the alpha-to-proton temperature ratio(T_(α)/T_(p))has been explored in the past. However, the modulation of this ratio with respect to the solar cycle has remained unexplored so far. We show solar-cycle modulation ofT_(α)/T_(p)andA_(c)using nearly three decades of in-situ observations from Wind spacecraft across distinct solar wind speed regimes and solar activity phases. Our results reveal that in the slow solar wind with velocity<400km s ⁻¹ , whereA_(c)happens to be typically>1 , the ratioT_(α)/T_(p)stays close to unity. This suggests frequent Coulomb collisions efficiently iron out temperature differences. In contrast, the fast wind with velocity>500km s ⁻¹ , whereA_(c)happens to be typically<1 , mass-proportional heating is most pronounced, withT_(α)/T_(p)often exceeding 4. The intermediate speed regime ( 400 - 500km s ⁻¹ ) represents a gradual transition between the slow and fast wind populations in terms of their solar-cycle dependence. This behavior reflects the changing dominance of high-speed streams from polar coronal holes during minima to denser slow wind during maxima. These results suggest that mass-proportional ion heating at 1 AU is not solely governed by local collisional physics but is significantly modulated by the solar cycle dependent variations in the solar wind sources.
Details
- Title: Subtitle
- Evidence for Solar-Cycle Modulation of the Alpha-to-Proton Temperature Ratio in Solar Wind
- Creators
- Aakash GuptaYogeshDibyendu ChakrabartyLeon OfmanGregory G Howes
- Resource Type
- Preprint
- Publication Details
- arXiv
- DOI
- 10.48550/arxiv.2608.10819
- ISSN
- 2331-8422
- Publisher
- arXiv
- Language
- English
- Date posted
- 08/11/2026
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9985218625902771
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