Publication Date:
2017-08-08
Description:
Recent studies have utilized different charge states of oxygen ions as a tracer for the origins of plasma populations in the magnetosphere of Earth, using O + as an indicator of ionospheric-originating plasma and O 6+ as an indicator of solar wind-originating plasma. These studies have correlated enhancements in O 6+ to various solar wind and geomagnetic conditions to characterize the dominant solar wind injection mechanisms into the magnetosphere, but did not include analysis of the temporal evolution of these ions. A 6 th -order Fourier expansion model based empirically on a superposed epoch analysis of geomagnetic storms observed by Polar is presented in this study to provide insight into the evolution of both ionospheric-originating and solar wind-originating plasma throughout geomagnetic storms. At high energies (~200 keV) the flux of O + and O 6+ are seen to become comparable in the outer magnetosphere. Moreover, while the density of O + is far higher than O 6+ , the two charge states have comparable pressures in the outer magnetosphere. The temperature of O 6+ is generally higher than that of O + , because the O 6+ is injected from pre-heated magnetosheath populations before undergoing further heating once in the magnetosphere. A comparison between the model results with O + observations from the Magnetospheric Multiscale (MMS) mission and the Van Allen Probes provides a validation of the model. In general, this empirical model agrees qualitatively well with the trends seen in both datasets. Quantitatively, the modeled density, pressure, and temperature almost always agree within a factor of at most 10, 5, and 2, respectively.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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