Measuring the Sources and Acceleration Mechanisms of Suprathermal Heavy Ions in Stream Interaction Regions near 1 AU

Date
2018
Authors
Filwett, Rachael Jo
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Abstract

Characterizing the sources and acceleration mechanisms of suprathermal (ST) ions is key for understanding particle acceleration and transport in the heliosphere. In this dissertation we examine the ~0.02-3.0 MeV nucleon -1 ST H-Fe ions in 41 stream interaction regions (SIRs) observed near 1 AU by Wind and ACE from January 1995 through December 2008. The SIR ST abundances vary with averaged monthly sunspot number, implying that the source population originates from prior solar and interplanetary activity. Although the mean SIR ST abundances are similar to average solar wind (SW) abundances, they are not well organized by the ion's mass-charge ratio (M/Q) or the first ionization potential (FIP), thus implying that if SIR ST ions originate from the SW then some portion of the latter must undergo pre-processing by as yet poorly understood mechanisms. Using the mean SW speed and the peak correlation time between upstream ST and SIR ST abundances we find that the acceleration location lies within ~1 AU upstream. The SIR ST energy spectra vary significantly from event-to-event, have a species-averaged spectral index steeper than E -1.5, and have species-independent rollover energies. These findings pose substantial challenges for CIR and SIR acceleration models and transport models that predict M/Q-dependent spectral rollovers due to interplanetary turbulence effects. Finally, we discuss pre-flight calibration results from a novel ST Ion Sensor (SIS) that will make high sensitivity measurements of ~3-70 keV/e ST ions and allow us to address key open questions regarding the origin and acceleration of ST ions in the heliosphere.

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Keywords
abundances, heliosphere, particle acceleration, solar wind, transport
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Department
Physics and Astronomy