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- Title
Sustained Oxygen Spectral Gaps and Their Dynamic Evolution in the Inner Magnetosphere.
- Authors
Chao Yue; Xu-Zhi Zhou; Bortnik, Jacob; Qiu-Gang Zong; Yuxuan Li; Jie Ren; Reeves, Geoffrey D.; Spence, Harlan E.
- Abstract
Van Allen Probes observations of ion spectra often show a sustained gap within a very narrow energy range throughout the full orbit. To understand their formation mechanism, we statistically investigate the characteristics of the narrow gaps for oxygen ions and find that they are most frequently observed near the noon sector with a peak occurrence rate of over 30%. The magnetic moment (µ) of the oxygen ions in the gap shows a strong dependence on magnetic local time (MLT), with higher and lower µ values in the morning and afternoon sectors, respectively. Moreover, we find through superposed epoch analysis that the gap formation also depends on geomagnetic conditions. Those gaps formed at lower magnetic moments (µ < 3,000 keV/G) are associated with stable convection electric fields, which enable magnetospheric ions to follow a steady drift pattern that facilitates the gap formation by corotational drift resonance. On the other hand, gaps with higher µ values are statistically preceded by a gradual increase of geomagnetic activity. We suggest that ions within the gap were originally located inside the Alfven layer following closed drift paths, before they were transitioned into open drift paths as the convection electric field was enhanced. The sunward drift of these ions, with very low fluxes, forms a drainage void in the dayside magnetosphere manifested as the sustained gap in the oxygen spectrum. This scenario is supported by particle-tracing simulations, which reproduce most of the observed characteristics and therefore provide new insights into inner magnetospheric dynamics.
- Subjects
RADIATION belts; VAN Allen radiation belts; GEOMAGNETISM; MAGNETOSPHERE; SOLAR magnetism
- Publication
Journal of Geophysical Research. Space Physics, 2021, Vol 126, Issue 4, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2020JA029092