Flux Enhancements of Field‐Aligned Low‐Energy O<sup>+</sup> Ion (FALEO) in the Inner Magnetosphere: A Possible Source of Warm Plasma Cloak and Oxygen Torus

Oxygen (O + ) ions in Earth's magnetosphere have attracted the attention of space physicists since they were discovered. The attraction mainly comes from their fundamental role in both the local and global dynamics of the magnetosphere. As an example of the former, we note that the presence of O + ions will largely change the local mass density and consequently modify the characteristics of and excitation conditions for various magnetospheric waves, like Alfven waves [e.g., Fraser et al., 2005] and electromagnetic ion cyclotron waves [e.g., Lee et al., 2019]. For the latter, it has been well established that O + ions usually dominate the energy density of the storm-time ring current and thus are believed to be the primary plasma species responsible for storm evolution [e.g., Daglis, 1997;Fu et al., 2001]. Besides, it has been proposed that O + ions might affect the global solar wind-magnetosphere coupling by modifying the dayside reconnection rate [e.g., Borovsky et al., 2008;Yu & Ridley, 2013], although this point has not been fully confirmed.The importance of O + ions stimulated extensively studies on their origination. In the light of the charge state, they are believed to have an Earth origination rather than the Sun. However, debates continue to this day on the more specific sources and their relative importance. At present, the most important source is suggested to be the high latitude ionosphere, which can be further divided into three regions: the dayside cusp, the polar cap, and the auroral oval [e.g., Chappell et al., 1987;Kronberg et al., 2014]. In general, forced by magnetospheric convection, ions from the high latitude ionosphere are first transported to the nightside magnetotail and then (part of them) convected back to the inner magnetosphere [e.g., Slapak & Nilsson, 2018]. Because of their magnetotail history, these ions are usually regarded as a nightside source of the inner magnetosphere. Obviously, ions would take a long time to arrive the inner magnetosphere in such a circulation. In addition to the nightside source, ionospheric O + outflows (IOOs) directly injected into the dayside [e.g.,

Section: Statisticsmentioning

confidence: 99%

mentioning

confidence: 99%

Ionospheric Oxygen Outflows Directly Injected Into the Inner Magnetosphere: Van Allen Probes Statistics

Liu

Zong

2022

“…In addition, bounce echoes of ionospheric outflows have been observed in the inner magnetosphere (e.g., Gkioulidou et al., 2019; Nosé et al., 2022). These echoes, along with corresponding primary beams, have facilitated the identification of a novel outflow oxygen ion population in a statistical manner (Z.‐Y.…”

Section: Introductionmentioning

confidence: 99%

Ion Acceleration and Corresponding Bounce Echoes Induced by Electric Field Impulses: MMS Observations

Li,

Liu,

Zong

et al. 2024

Dayside magnetosphere interactions are essential for energy and momentum transport between the solar wind and the magnetosphere. In this study, we investigate a new phenomenon within this regime. Sudden enhancements of ion fluxes followed by repeating dropouts and recoveries were observed by Magnetospheric Multiscale on 5 November 2016, which is the very end of the recovery phase from a moderate geomagnetic storm. These repetitive flux variations display energy‐dispersive characteristics with periods relevant to ion bounce motion, suggesting they are corresponding echoes. Alongside the flux variations, bipolar electric field impulses originating from external sources were detected. We traced the source region of the initial injection and found it is located near the spacecraft's position. To elucidate the underlying physics, a test‐particle simulation is conducted. The results reveal that radial transport resulting from impulse‐induced acceleration can give rise to these echoes. Observations demonstrate dayside magnetosphere interactions are more common than we previously considered, which warrants further research.

Assessing the Sources of the O⁺ in the Plasma Sheet

Liao,

Kistler,

Mouikis

et al. 2024

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 YGSM‐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 RE, 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.