Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
Volume 118, Issue 7, Pages 4441-4464Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/jgra.50371
Keywords
heavy ions; ion energization; ring current; O plus dynamics; storm; substorm
Categories
Funding
- Van Allen Probes
- JHU/APL [937836, 967399]
- NASA [NAS5-01072]
- RBSP-ECT
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In situ observations and modeling work have confirmed that singly charged oxygen ions, O+, which are of Earth's ionospheric origin, are heated/accelerated up to >100keV in the magnetosphere. The energetic O+ population makes a significant contribution to the plasma pressure in the Earth's inner magnetosphere during magnetic storms, although under quiet conditions, H+ dominates the plasma pressure. The pressure enhancements, which we term energization, are caused by adiabatic heating through earthward transport of source population in the plasma sheet, local acceleration in the inner magnetosphere and near-Earth plasma sheet, and enhanced ion supply from the topside ionosphere. The key issues regarding stronger O+ energization than H+ are nonadiabatic local acceleration, responsible for increase in O+ temperature, and more significant O+ supply than H+, responsible for the increase in O+ density. Although several acceleration mechanisms and O+ supply processes have been proposed, it remains an open question what mechanism(s)/process(es) play the dominant role in stronger O+ energization. This review paper summarizes important previous spacecraft observations, introduces the proposed mechanisms/processes that generate O+-rich energetic plasma population, and outlines possible scenarios of O+ pressure abundance in the Earth's inner magnetosphere.
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