Van Allen Probes Observations of Oxygen Ions at the Geospace Plume

• Main Authors: Foster, John C (Contributor), Erickson, Philip J (Author)
• Other Authors: Haystack Observatory (Contributor)
• Format: Article
• Language: English
• Published: Frontiers Media SA, 2021-08-10T21:58:53Z.
• Subjects: Article
• Online Access: Get fulltext

 The geospace plume couples the ionosphere, plasmasphere, and magnetosphere from sub-auroral regions to the magnetopause, on polar field lines, and into the magnetotail. We describe Van Allen Probes observations of ionospheric O+ ions at altitudes of 3-6 R[subscript E] in the near vicinity of the geospace plume in the noon and post-noon sector. The temporal variation of warm ion fluxes observed as a function of time on a moving spacecraft is complicated by changing spacecraft position and complex ion drift paths and velocities that are highly sensitive to ion energy, pitch angle and L value. In the "notch" region of lower density plasma outside the morning-side plasmapause, bi-directionally field aligned fluxes of lower energy (<5 keV) ions, following corotation-dominated drift trajectories from the midnight sector, are excluded from geospace plume field lines as they are deflected sunward in the plume flow channel. In general, O+ at ring current energies (∼10 keV) is bi-directionally field aligned on plume field lines, while lower energy O⁺(<3 keV) are absent. The observation of ion plumes with energies increasing from ∼1 keV- > 20 keV in the dusk sector outer plasmasphere is interpreted as evidence for localized ionospheric O+ outflow at the outer edge of the geospace plume with subsequent O+ acceleration to >50 keV in <30 min during the ions' sunward drift.