In this study, we employ the combined charged particle measurements from Integrated Science Investigation of the Sun on board the Parker Solar Probe (PSP) and Energetic Particle Detector on board the Solar Orbiter (SolO) to study the composition variation of the solar energetic particle (SEP) event occurring on 2023 May 16. During the event, SolO and PSP were located at a similar radial distance of ∼0.7 au and were separated by ∼60° in longitude. The footpoints of both PSP and SolO were west of the flare region, but the former was much closer (18° versus 80°). Such a distribution of observers is ideal for studying the longitudinal dependence of the ion composition with the minimum transport effects of particles along the radial direction. We focus on H, He, O, and Fe measured by both spacecraft in sunward and antisunward directions. Their spectra are in a double power-law shape, which is fitted best by the Band function. Notably, the event was Fe rich at PSP, where the mean Fe/O ratio at energies of 0.1–10 Mev nuc−1 was 0.48, higher than the average Fe/O ratio in previous large SEP events. In contrast, the mean Fe/O ratio at SolO over the same energy range was considerably lower at 0.08. The Fe/O ratio between 0.5 and 10 MeV nuc−1 at both spacecraft is nearly constant. Although the He/H ratio shows energy dependence, decreasing with increasing energy, the He/H ratio at PSP is still about twice as high as that at SolO. Such a strong longitudinal dependence of element abundances and the Fe-rich component in the PSP data could be attributed to the direct flare contribution. Moreover, the temporal profiles indicate that differences in the Fe/O and He/H ratios between PSP and SolO persisted throughout the entire event rather than only at the start.

中文翻译：

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SolO 和 PSP 观测到 2023 年 5 月 16 日太阳高能粒子事件的成分变化


在这项研究中，我们利用帕克太阳探测器 （PSP） 上的太阳综合科学调查和太阳轨道飞行器 （SolO） 上的高能粒子探测器的组合带电粒子测量来研究 2023 年 5 月 16 日发生的太阳高能粒子 （SEP） 事件的成分变化。在该事件期间，SolO 和 PSP 位于 ∼0.7 au 的相似径向距离上，经度相距 ∼60°。PSP 和 SolO 的足迹都在耀斑区域的西边，但前者更近（18° 对 80°）。这样的观察者分布非常适合研究离子组成的纵向依赖性，而粒子沿径向的传输效应最小。我们专注于航天器在朝阳和反朝阳方向上测量的 H、He、O 和 Fe。它们的光谱呈双幂律形状，最适合 Band 函数。值得注意的是，该事件在 PSP 处富含铁，其中 0.1-10 Mev nuc-1 能量下的平均 Fe/O 比率为 0.48，高于以前大型 SEP 事件中的平均 Fe/O 比率。相比之下，在相同能量范围内，SolO 的平均 Fe/O 比率要低得多，为 0.08。两个航天器的 Fe/O 比值在 0.5 和 10 MeV nuc−1 之间几乎是恒定的。尽管 He/H 比值表现出能量依赖性，随着能量的增加而降低，但 PSP 的 He/H 比值仍然比 SolO 高出约两倍。PSP 数据中元素丰度和富含 Fe 的成分的如此强的纵向依赖性可归因于直接耀斑贡献。此外，时间图谱表明，PSP 和 SolO 之间 Fe/O 和 He/H 比率的差异在整个事件中持续存在，而不仅仅是在开始时。