Extreme Kinematics of the 2017 September 10 Solar Eruption and the Spectral Characteristics of the Associated Energetic Particles

TL;DR

This study analyzes the extreme kinematics of the 2017 September 10 solar eruption, its associated energetic particles, and how magnetic connectivity influenced the observed properties of the ground level enhancement event.

Contribution

It provides detailed analysis of the highest observed CME acceleration and speed in the SOHO era, linking shock formation and particle release heights to magnetic connectivity.

Findings

CME had one of the highest accelerations and speeds observed.

Poor magnetic connectivity contributed to low intensity and softer spectra.

Shock formation and particle release heights are consistent with previous GLE events.

Abstract

We report on the 2017 September 10 ground level enhancement (GLE) event associated with a coronal mass ejection (CME) whose initial acceleration (~9.1km s^-2) and initial speed (~4300 km/s) were among the highest observed in the SOHO era. The GLE event was of low intensity (~4.4% above background) and softer-than-average fluence spectrum. We suggest that poor connectivity (longitudinal and latitudinal) of the source to Earth compounded by the weaker ambient magnetic field contributed to these GLE properties. Events with similar high initial speed either lacked GLE association or had softer fluence spectra. The shock-formation height inferred from the metric type II burst was ~1.4 Rs, consistent with other GLE events. The shock height at solar particle release (SPR) was ~4.4+/-0.38 Rs, consistent with the parabolic relationship between the shock height at SPR and source longitude. At SPR, the eastern flank of the shock was observed in EUV projected on the disk near the longitudes magnetically connected to Earth: W60 to W45.