Spatial Organization of Seven Extreme Solar Energetic Particle Events

Abstract

Abstract Emission of relativistic protons and helium responsible for extreme solar particle events (ground level enhancements (GLEs)) is often structured. We investigate its organization depending on the eruption stage characterized by the heliocentric height of associated coronal mass ejections (CMEs). Seven GLEs are considered: events on 1997 November 6, 1998 May 2, 2000 July 14, 2001 December 26, 2003 November 2, 2006 December 13, and 2012 May 17, which are half of the SOlar and Heliospheric Observatory (SOHO )-era GLEs, excluding very weak events. Count-rate profiles of the GLEs plotted as a function of the CME height reveal two types (or two components) of the high-energy particle emission. The first component rises in a step-like manner during the CME transit from 2 R ⊙ to 3 R ⊙, when the CME exits from predominantly closed coronal magnetic structures, irrespective of the CME speed (type H). This component is of coronal origin. The second component of the GLE-producing particles starts to rise when CME is at about 4 R ⊙, achieves its maximum at 6–10 R ⊙, and declines shortly after that (type J). The type J particle injection into the interplanetary space coincides with the decametric–hectometric radio burst complex that includes enhanced emission of type II and concurrent low-frequency type III bursts, indicative of the CME interaction with a streamer-like structure at a few solar radii from the Sun. Those could be delayed particles from the flare region. A possible additional contribution of the CME-bow-shock acceleration in unstructured solar wind is not large in the two considered types of events.