Physics – Plasma Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh24b..01b&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH24B-01
Physics
Plasma Physics
[2102] Interplanetary Physics / Corotating Streams, [2114] Interplanetary Physics / Energetic Particles, [2152] Interplanetary Physics / Pickup Ions, [7845] Space Plasma Physics / Particle Acceleration
Scientific paper
Interstellar pickup He+ contributes about ~25% of the total He population in corotating interaction regions (CIRs). It has been known that He+ pickup ion density shows annual variations due to gravitational focusing of the Sun. However, the variations in the CIR energetic ions reflecting the temporal changes in the He+ pickup ions remain unproven. In this work we examine the elemental composition and energy spectra of the 0.1 - 1 MeV/nucleon heavy ions accelerated in CIRs. For the investigations we use data from the SIT (Suprathermal Ion Telescope) instruments on board the two STEREO spacecraft (S/C) acquired over the extended minimum phase of Solar Cycle 23 from January 2007 to December 2010. The two STEREO S/C are well separated in heliolongitude, and enter the helium focusing cone at different times. During the investigated period instruments on STEREO observed more than 70 CIR events, allowing one to study CIR ion abundances during solar minimum conditions with unprecedented high statistics. The observations reveal annual variations of relative ion abundances in the CIRs during the 2007-2008 period. In 2010 the elemental composition in CIRs were influenced by solar energetic particle events. We find that the CIR He/H and He/O ratios were enhanced in the period of the focusing cone traversals. By combining the SIT observations with the solar wind plasma observations from the PLASTIC instrument on the STEREO S/C we discuss the correlations between the energy spectral slopes of the suprathermal heavy ions and the He+ pickup ion count rates. In the investigated period the solar wind was dominated by stably recurring CIRs. This could lead to more uniform particle injection and acceleration conditions in the CIRs, making it possible to see the signatures of the focusing cone in the energetic ion population.
Bučík Radoslav
Klecker Berndt
Korth Alex
Mall Ulrich
Mason Glenn M.
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