Corotating Shock Waves and the Solar-Wind Source of Energetic Ion Abundances: Power Laws in A/Q

TL;DR

This study reveals that energetic ion abundances in corotating interaction regions follow a power-law dependence on A/Q, reflecting the solar wind composition and providing insights into shock acceleration processes.

Contribution

It demonstrates that ion abundances in CIRs mirror solar wind A/Q ratios with a power-law dependence, linking shock acceleration to solar wind composition.

Findings

Ion abundances follow a (A/Q)^a power law with a negative a.

The A/Q dependence decreases with distance from shocks.

In a special case, abundances directly reflect the fast solar wind.

Abstract

We find that element abundances in energetic ions accelerated by shock waves formed at corotating interaction regions (CIRs) mirror the abundances of the solar wind modified by a decreasing power-law dependence on the mass-to-charge ratio A/Q of the ions. This behavior is similar in character to the well-known power-law dependence on A/Q of abundances in large gradual solar energetic particles (SEP). The CIR ions reflect the pattern of A/Q, with Q values of the source plasma temperature or freezing-in temperature of 1.0 - 1.2 MK typical of the fast solar wind in this case. Thus the relative ion abundances in CIRs are of the form (A/Q)**a where a is nearly always negative and evidently decreases with distance from the shocks, which usually begin beyond 1 AU. For one unusual historic CIR event where a ~ 0, the reverse shock wave of the CIR seems to occur at 1 AU, and these abundances of the energetic ions become a direct proxy for the abundances of the fast solar wind.