The Link Between Wedge‐Like and Nose‐Like Ion Spectral Structures in the Inner Magnetosphere

Abstract

The wedge‐like and nose‐like ion spectral structures, named after their characteristic shapes in the energy‐time spectrograms, appear to be distinctively different structures in the Earth's inner magnetosphere. Here. we present a case study with conjugate observations from the Arase spacecraft and the twin Van Allen Probes on July 1 and 2, 2017, which displayed the characteristic signatures of the wedge‐like and nose‐like ion structures, respectively. When the spacecraft nearly intersected at L = 2.8, the two structures overlapped with enhanced ion fluxes in the energy range of 1–10 keV. These observations suggest that the wedge‐like and nose‐like spectral signatures are merely the manifestations of one single structure along different spacecraft trajectories. This finding is further validated by the reproduction of both structures from a particle‐tracing model, which also indicates their formation processes associated with the intermittent substorm injections in the nightside magnetosphere.

Multipoint Measurement of Fine‐Structured EMIC Waves by Arase, Van Allen Probe A, and Ground Stations

“…The corresponding measurements of the omnidirectional proton fluxes by Arase/LEP‐i and RBSP‐A/ECT‐HOPE are displayed in Figures 3b and 3f. Both Arase and RBSP‐A detect ion nose structures near the inner edge of the duskside plasma sheet (e.g., Ren et al., 2021), and no periodic changes were observed in the proton distribution during the interval of the fine‐structured EMIC wave activity.…”

Statistical study of “trunk-like” heavy ion structures in the inner magnetosphere

“…In addition, Yue C et al (2021b) further investigated the MLT dependence of the sustained proton and oxygen spectral gaps and found that the different MLT distributions between proton and oxygen spectral gaps are primarily caused by the different charge exchange loss rates. Ren J et al (2021) presented a case study to show that nose-like and wedge-like spectral structures could be merely manifestations of one single structure along different spacecraft trajectories.…”

MLT‐Dependence of Sustained Spectral Gaps of Proton and Oxygen in the Inner Magnetosphere

“…The inner magnetosphere is a highly dynamic and complex system with various populations (including the coexisting and overlapping cold plasmasphere, energetic ring current, and relativistic radiation belt particles), which are governed by the time varying electric and magnetic fields (e.g., Yue, Bortnik, Chen, et al., 2017; Yue, Bortnik, Thorne, et al., 2017; Yue et al., 2016, 2018, 2019). Especially, ions with energy from 1 to 20 keV are strongly affected by the competition between electric field drifts and the magnetic gradient and curvature drifts, which may generate different type of ions spectral structures, such as “nose‐like” structures (e.g., Buzulukova et al., 2003; Ebihara et al., 2004; Fennell et al., 1998; Ferradas et al., 2016a, 2016b; Ganushkina et al., 2001; Li et al., 2000; Smith & Hoffman, 1974; Vallat et al., 2007), “wedge‐like” dispersions (e.g., Ebihara et al., 2001; Ren et al., 2020, 2021; Yamauchi et al., 2006; Zhou et al., 2020), “trunk‐like” structures (Zhang et al., 2015), low‐energy “finger” (e.g., Wang et al., 2020), and ion spectral gaps or stagnation dips (e.g., Buzulukova et al., 2002; Fennell et al., 1981; Kaye et al., 1981; Kistler & Mouikis, 2016; Kistler et al., 1989; Kovrazhkin et al., 1999; Lennartsson et al., 1979; Shirai et al., 1997; Yue et al., 2021).…”