Anomalously low C{sup 6+}/C{sup 5+} ratio in solar wind: ACE/SWICS observation

Journal Article · Fri Mar 25 04:00:00 EDT 2016 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.4943807· OSTI ID:22590899

Landi, E.; Kocher, M.; Lepri, S. T.; Fisk, L. A.; Zurbuchen, T. H. ^[1]

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1. Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, 48105 (United States)

The Carbon and Oxygen ionization states in the solar wind plasma freeze-in within 2 solar radii (R{sub s}) from the solar surface, and then they do not change as they propagate with the solar wind into the heliosphere. Therefore, the O{sup 7+}/O{sup 6+} and C{sup 6+}/C{sup 5+} charge state ratios measured in situ maintain a record of the thermal properties (electron temperature and density) of the inner corona where the solar wind originates. Since these two ratios freeze-in at very similar height, they are expected to be correlated. However, an investigation of the correlation between these two ratios as measured by ACE/SWICS instrument from 1998 to 201l shows that there is a subset of “Outliers” departing from the expected correlation. We find about 49.4% of these Outliers is related to the Interplanetary Coronal Mass Ejections (ICMEs), while 49.6% of them is slow speed wind (V{sub p} < 500 km/s) and about 1.0% of them is fast solar wind (V{sub p} > 500 km/s). We compare the outlier-slow-speed wind with the normal slow wind (defined as V{sub p} < 500 km/s and O{sup 7+}/O{sup 6+} > 0.2) and find that the reason that causes the Outliers to depart from the correlation is their extremely depleted C{sup 6+}/C{sup 5+} ratio which is decreased by 80% compared to the normal slow wind. We discuss the implication of the Outlier solar wind for the solar wind acceleration mechanism.

• OSTI ID: 22590899
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 1720; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ACCELERATION
ASTROPHYSICS
CARBON IONS
CHARGE STATES
COMPARATIVE EVALUATIONS
CORRELATIONS
ELECTRON DENSITY
ELECTRON TEMPERATURE
HELIOSPHERE
IONIZATION
MULTICHARGED IONS
PLASMA
SOLAR WIND
THERMODYNAMIC PROPERTIES