Ground Level Enhancement in the 2014 January 6 Solar Energetic Particle Event

TL;DR

This paper analyzes the 2014 January 6 solar energetic particle event, which caused a small ground level enhancement, by examining CME dynamics, radio bursts, and neutron monitor data to understand its characteristics and compare it with previous GLEs.

Contribution

It provides detailed measurements of CME heights and timing related to the GLE, highlighting the event's unique features within solar cycle 24 and comparing it to past GLEs.

Findings

The GLE was primarily observed at South Pole neutron monitors.

CME height at GLE particle release was 2.96 Rs.

This GLE was one of the smallest and behind-the-limb GLEs of cycles 23 and 24.

Abstract

We present a study of the 2014 January 6 solar energetic particle (SEP) event, which produced a small ground level enhancement (GLE), making it the second GLE of this unusual solar cycle 24. This event was primarily observed by the South Pole neutron monitors (increase of ~2.5%) whereas a few other neutron monitors recorded smaller increases. The associated coronal mass ejection (CME) originated behind the western limb and had the speed of 1960 km/s. The height of the CME at the start of the associated metric type II radio burst, which indicates the formation of a strong shock, was measured to be 1.61 Rs using a direct image from STEREO-A/EUVI. The CME height at the time of GLE particle release (determined using the South Pole neutron monitor data) was directly measured as 2.96 Rs, from the STEREO-A/COR1 white-light observations. These CME heights are consistent with those obtained for the GLE71, the only other GLE of the current cycle as well as cycle-23 GLEs derived using back-extrapolation. GLE72 is of special interest because it is one of the only two GLEs of cycle 24, one of the two behind-the-limb GLEs and one of the two smallest GLEs of cycles 23 and 24.