Kazushi Asamura

Abstract Using Arase satellite observations, this study provides a comprehensive statistical analysis of ions (H⁺, He⁺, O⁺) and electron contributions to the total ring current pressure during storms with two different drivers. The results demonstrate the effect of different solar wind drivers on the composition, energy distribution, and spatial characteristics of the ring current. Using 32 CIR‐ and 30 Interplanetary Coronal Mass Ejection (ICME)‐driven storms, we characterize the ring current pressure evolution during the prestorm, main, early‐recovery, and late‐recovery storm phases as a function of magnetic local time and L‐shell. In CIR‐driven storms, H⁺ ions are the dominant (∼70%) contributor to the total ring current pressure during main/early recovery phases and increasing to ∼80% during late recovery. In contrast, the O⁺ pressure (E = 20–50 keV) response is significantly stronger in ICME‐driven storms contributing ∼40% to the overall pressure during the main/early recovery phases and even dominate (∼53%) in certain MLT sectors. Additionally, ICME‐driven storms tend to have peak pressure at lower L‐shells (L ≈ 3–4), while CIR‐driven storms show pressure peaks at slightly higher L‐shells (L ≈ 4–5). Interestingly, electron pressure also plays a notable role in specific MLT sectors, contributing ∼18% (03–09 MLT) during the main phase of CIR‐driven storms and ∼11% (21–03 MLT) during ICME‐driven storms. The results highlight that the storm time electron pressure plays a crucial role in the ring current buildup. Another noteworthy feature of this study is that Arase's fine‐energy resolution and broad coverage enable a detailed investigation of energy‐dependent ring current dynamics.

Abstract The interaction between lunar magnetic anomalies and the solar wind plasma creates unique structures known as “lunar mini‐magnetospheres,” which reflect and partially shield the lunar surface from impinging solar wind protons. Using data from the Sub‐KeV Atom Reflecting Analyzer onboard Chandrayaan‐1, we produce new surface maps of energetic neutral atom (ENA) and reflected proton emissions. We show that solar wind proton precipitation can be reduced by up to 80% inside magnetic anomalies and increased by up to 50% on scales larger than 1,000 km around magnetic anomalies. The morphology of these proton precipitation enhancement and depletion regions varies differently as a function of upstream solar wind dynamic pressure for small, isolated anomalies compared to the large South Pole‐Aitken (SPA) magnetic cluster. In contrast to small magnetic anomalies, which are compressed and less effective at shielding the surface from the solar wind at high dynamic pressures, the SPA magnetic cluster creates a large “mini‐magnetosphere” that alters proton precipitation patterns on global‐scales (>1,000 km) inside and around the cluster. We show that this behavior may result from the interaction between protons reflected by the SPA magnetic anomaly cluster and the solar wind.