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Energization of O + ions in the Earth's inner magnetosphere and the effects on ring current buildup: A review of previous observations and possible mechanisms
Author(s) -
Keika Kunihiro,
Kistler Lynn M.,
Brandt Pontus C.
Publication year - 2013
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/jgra.50371
Subject(s) - magnetosphere , ring current , plasma sheet , physics , population , ionosphere , plasma , atmospheric pressure plasma , atomic physics , ion , geophysics , geomagnetic storm , computational physics , solar wind , nuclear physics , demography , quantum mechanics , sociology
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 >100 keV 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.