STEREO Observations of Energetic Ions in Corotating Interaction Regions During the May 2007 Solar Events

Abstract

Elemental composition and energy spectra of ∼ 0.1 -1.0 MeV/n heavy ions were analyzed in two corotating interaction region (CIR) events starting on 18 May (CIR1), and 24 May (CIR2), 2007, that occurred during two weak solar energetic particle (SEP) events. The data were taken by the Suprathermal Ion Telescope (SIT) instruments onboard STEREO-A and B. The ion intensity increases related to the CIR2 were much more pronounced compared to those associated with the CIR1, although the total pressure, the magnetic field magnitude and the speed difference between high and slow solar wind were less enhanced. We found that the ratio of CIR2 to CIR1 helium fluence decreases with energy as a power -law below ∼ 1 MeV/n. The energy spectra of hydrogen and helium inside the CIR2 region are much softer compared to the spectra observed in the CIR1 region. Based on these findings, we argue that the larger intensities in the CIR2 event could be due to an additional source population. The elemental abundances in CIR2 and the high-speed stream of the CIR1 region have a SEP-like composition. The energy spectra of hydrogen and helium inside the CIR2 were close to the preceding SEP event spectra. The similarity in the elemental abundances and in the spectral slopes suggests that the seed population of CIR2 are ions from the preceding SEP event. For the CIR1 event the ions seem to be contaminated by SEPs.

Acceleration of Energetic Ions in Corotating Interaction Region near 1.5 au: Evidence from MAVEN

“…Double power laws are fitted, one with E −1.88 for flux below 0.2 MeV and the second one with E −2.78 for the flux between 0.2 to 3 MeV. These spectral indices are similar to those reported by Bučík et al (2009) for the May 2007 events. To see whether we can expect higher energy particles at the energy ranges of GOES, the ACE spectrum is extrapolated to 30 MeV with the same power law.…”

On acceleration of <1 MeV/n He ions in the corotating compression regions near 1 AU: STEREO observations

“…For this event the boundaries of the CIR were not clear due to preceding ICME. In addition, the CIR associated ion intensity was affected by the 23 May 2007 SEP event (Bučík et al, 2009). We searched for other STEREO SEP and CIR events coincidences.…”

Spatial and temporal variations of CIRs: Multi-point observations by STEREO

“…Bučík et al, 2009a;Rouillard et al, 2008;Jian et al, 2009;Gó mez-Herrero et al, 2009;Dresing et al, 2009;Bučík et al, 2009b;Mason et al, 2009;Simunac et al, 2009;Tappin and Howard, 2009;Leske et al, 2010;Wood et al, 2010).…”