Heavy-ion dominance near Cluster perigees

TitleHeavy-ion dominance near Cluster perigees
Publication TypeJournal Article
Year of Publication2015
AuthorsFerradas, CP, Zhang, J-C, Kistler, LM, Spence, HE
JournalJournal of Geophysical Research: Space Physics
Paginationn/a - n/a
Date Published10/2015
Keywordscharge exchange; Cluster; heavy ions; inner magnetosphere; plasma sheet; ring current
AbstractTime periods in which heavy ions dominate over H+ in the energy range of 1-40 keV were observed by the Cluster Ion Spectrometry (CIS)/COmposition DIstribution Function (CODIF) instrument onboard Cluster Spacecraft 4 at L-values less than 4. The characteristic feature is a narrow flux peak at around 10 keV that extends into low L-values, with He+ and/or O+ dominating. In the present work we perform a statistical study of these events and examine their temporal occurrence and spatial distribution. The observed features, both the narrow energy range and the heavy-ion dominance, can be interpreted using a model of ion drift from the plasma sheet, subject to charge exchange losses. The narrow energy range corresponds to the only energy range that has direct drift access from the plasma sheet during quiet times. The drift time to these locations from the plasma sheet is > 30 hours, so that charge exchange has a significant impact on the population. We show that a simple drift/loss model can explain the dependence on L-shell and MLT of these heavy-ion-dominant time periods.
Short TitleJ. Geophys. Res. Space Physics

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