Comparative Analysis of Iron to Oxygen Ratios Between CIRs and the Bulk Solar Wind

Abstract:

Corotating interaction region (CIR) events accelerate particles to MeV energies. Here we investigate the seed populations of these events. In a paper in 2019, Robert Allen remarks on a notable enhancement in the iron-oxygen ratio in CIR and stream interaction region (SIR) events during the declining phase of the solar cycle. In this study, we investigate this ‘lagging’ enhancement by attempting to analyze the seed populations of the CIR and SIR events during this time. We use data from the WIND EPACT-STEP instrument to compare the 0.5 to 2.0 MeV iron to oxygen ratios in 77 CIR and SIR events between 1995 and 2018 with quiet-time Fe/O ratios for measurements upstream of each of these events. In doing this, we found a loose positive correlation between the quiet-time Fe/O ratio and the event Fe/O ratio. We also found that the Fe/O ratios in each of the CIR/ SIR events was much higher, on average, than that of the bulk solar wind. This could mean that the bulk solar wind is acting as a majority of the seed population for CIR and SIR events. However, the enhancement in Fe/O when compared to the ‘quiet’ solar wind leads us to believe that the sole seed population for these events is not the bulk solar wind.