Spatial Distribution of Element Abundances and Ionization States in Solar Energetic-Particle Events

TL;DR

This study uses abundance measurements from spacecraft to map the spatial distribution of element ionization states and plasma temperatures in solar energetic-particle events, revealing variations along shock waves.

Contribution

It introduces a novel method to determine ion charge states and source plasma temperatures remotely, using abundance enhancements and A/Q ratios in SEP events.

Findings

Identified a case of shock wave dispatching ions from different plasma temperatures.

Observed temperature variations over large longitudinal separations.

Demonstrated the technique's potential for remote plasma diagnostics.

Abstract

We have studied the spatial and temporal distribution of abundances of chemical elements in large "gradual" solar energetic-particle (SEP) events, and especially the source plasma temperatures, derived from those abundances, using measurements from the Wind and Solar TErestrial RElations Observatory (STEREO) spacecraft, widely separated in solar longitude. A power-law relationship between abundance enhancements and mass-to-charge ratios [A/Q] of the ions can be used to determine Q-values and source plasma temperatures at remote spacecraft with instruments that were not designed for charge-state measurements. We search for possible source variations along the accelerating shock wave, finding one clear case where the accelerating shock wave appears to dispatch ions from 3.2+-0.8 MK plasma toward one spacecraft and those from 1.6+-0.2 MK plasma toward another, 116 deg away. The difference persists three days and then fades away. Three other SEP events show less-extreme variation in source temperatures at different spacecraft, in one case observed over 222 deg in longitude. This initial study shows how the power-law relation between abundance enhancements and ion A/Q-values pro-vides a new technique to determine Q and plasma temperatures in the seed population of SEP ions over a broad region of space using remote spacecraft with instruments that were not originally designed for measurements of ionization states.