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Abstract On 24 April 2023, an ICME reached Earth's orbit. The solar wind density dropped to 0.3 amu/cc while the IMF strength was about 25 nT. As a result, the solar wind flow transitions to a sub‐Alfvénic state with an Alfvén Mach number of 0.4. We carry out global magnetohydrodynamic simulations to investigate the responses of Earth's magnetosphere to the ICME ejecta. The results show the formation of Alfvén wings as the solar wind becomes sub‐Alfvénic. Furthermore, the sub‐Alfvénic period was characterized by the dominance of the IMF component, causing the Alfvén wings to extend toward the dawn and dusk flanks. We investigate the global magnetospheric convection of this sub‐ Alfvénic case and find that the overall convection is mediated by the Alfvén wings, while the magnetic field convection in inner magnetosphere is similar to the super‐Alfvénic case. 

Abstract To study the average contributions of the cusp outflow through the lobes and of the nightside auroral outflow to the O⁺in the plasma sheet (PS), we performed a statistical study of tailward streaming O⁺in the lobes, plasma sheet boundary layer|the plasma sheet boundary layer (PSBL) and the PS, using MMS/Hot Plasma Composition Analyzer (HPCA) data from 2017 to 2020. Similar spatial patterns illustrate the entry of cusp‐origin O⁺from the lobes to the PS through the PSBL. There is an Y_GSM‐dependent energy pattern for the lobe O⁺, with low‐energy O⁺streaming closer to the tail center and high energy (1–3 keV) O⁺streaming near the flanks. Low energy (1–100 eV) O⁺from the nightside auroral oval is identified in the near‐Earth PSBL/PS with high‐density (>0.02 cm⁻³), and energetic (>3 keV) streaming O⁺with similar density (∼0.013 cm⁻³) is observed further out on the duskside of the PSBL/PS. The rest of the nightside auroral O⁺in the PSBL is mixed with O⁺coming in from the lobe, making it difficult to distinguish the source. We estimated the contributions of the different sources of H⁺and O⁺ions through the PS between 7 and 17 R_E, using estimates from this work and data extracted from previous studies. We conclude that, during quiet times, the majority of the near‐Earth PS H⁺are from the cusps, the polar wind and Earthward convection from the distant tail. Similarly, while the O⁺in the same region has a mixed source, cusp origin outflow provides the highest contribution. 

Recently it has been identified that our Moon had an extensive magnetosphere for several hundred million years soon after it was formed when the Moon was within 20 Earth Radii (R_E) from the Earth. Some aspects of the interaction between the early Earth-Moon magnetospheres are investigated by mapping the interconnected field lines between the Earth and the Moon and investigating how the early lunar magnetosphere affects the magnetospheric dynamics within the coupled magnetospheres over time. So long as the magnetosphere of the Moon remains strong as it moves away from the Earth in the antialigned dipole configuration, the extent of the Earth’s open field lines decreases. As a result, at times it significantly changes the structure of the field-aligned current system, pushing the polar cusp significantly northward, and forcing magnetotail reconnection sites into the deeper tail region. In addition, the combined magnetospheres of the Earth and the Moon greatly extend the number of closed field lines enabling a much larger plasmasphere to exist and connecting the lunar polar cap with closed field lines to the Earth. That configuration supports the transfer of plasma between the Earth and the Moon potentially creating a time capsule of the evolution of volatiles with depth. This paper only touches on the evolution of the early Earth and Moon magnetospheres, which has been a largely neglected space physics problem and has great potential for complex follow-on studies using more advanced tools and due to the expected new lunar data coming in the next decade through the Artemis Program. 

Collisionless magnetic reconnection typically requires kinetic treatment that is, in general, computationally expensive compared to fluid-based models. In this study, we use the magnetohydrodynamics with an adaptively embedded particle-in-cell (MHD-AEPIC) model to study the interaction of two magnetic flux ropes. This innovative model embeds one or more adaptive PIC regions into a global MHD simulation domain such that the kinetic treatment is only applied in regions where the kinetic physics is prominent. We compare the simulation results among three cases: (1) MHD with adaptively embedded PIC regions, (2) MHD with statically (or fixed) embedded PIC regions, and (3) a full PIC simulation. The comparison yields good agreement when analyzing their reconnection rates and magnetic island separations as well as the ion pressure tensor elements and ion agyrotropy. In order to reach good agreement among the three cases, large adaptive PIC regions are needed within the MHD domain, which indicates that the magnetic island coalescence problem is highly kinetic in nature, where the coupling between the macro-scale MHD and micro-scale kinetic physics is important.