太阳风中α粒子与质子温度比受太阳活动周调制的证据
Evidence for Solar-Cycle Modulation of the Alpha-to-Proton Temperature Ratio in Solar Wind
中文总结 AI 辅助
本研究利用Wind航天器近三十年原位观测，首次证实太阳风α粒子-质子温度比存在太阳活动周调制，揭示不同速度风区的加热特性差异，表明1 AU处离子质量比例加热受太阳风源区周变调制。
中文摘要 AI 辅助
过去已有研究探讨了碰撞年龄$(A_c)$对α粒子-质子温度比$(T_α/T_p)$的影响，但该比值随太阳活动周的调制规律此前尚未得到探究。我们利用Wind航天器近三十年的原位观测数据，在不同太阳风速度区间和太阳活动相位下，揭示了$T_α/T_p$与$A_c$的太阳活动周调制特征。结果显示，在速度$<400$ km s$^{-1}$的慢太阳风中，$A_c$通常大于1，此时$T_α/T_p$接近1，表明频繁的库仑碰撞有效消除了温度差异。相比之下，在速度$>500$ km s$^{-1}$的快太阳风中，$A_c$通常小于1，质量比例加热效应最为显著，$T_α/T_p$常超过4。中速风区间（$400$-$500$ km s$^{-1}$）则呈现出慢风与快风群体太阳周依赖特性之间的渐变过渡。这种行为反映了从太阳活动极小期极冕洞的高速流主导，到极大期更稠密的慢风主导的转变。这些结果表明，1天文单位处的离子质量比例加热并非仅由局地碰撞物理过程决定，还受到太阳风源区随太阳活动周变化的显著调制。
英文摘要
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 of $T_α/T_p$ and $A_c$ 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 $<400$ km s$^{-1}$, where $A_c$ happens to be typically $>1$, the ratio $T_α/T_p$ stays close to unity. This suggests frequent Coulomb collisions efficiently iron out temperature differences. In contrast, the fast wind with velocity $>500$ km s$^{-1}$, where $A_c$ happens to be typically $<1$, mass-proportional heating is most pronounced, with $T_α/T_p$ often exceeding 4. The intermediate speed regime ($400$-$500$ km 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.
