Effect of Some Solar Energetic Events on Cosmic Ray (CR) Ground Level Enhancement (GLE)

Okpala Kingsley Chukwudi,Abejoye Sylvester Ajisafe,Tsor James

doi:10.11648/j.ijass.20200801.11

Abstract

Ground Level Enhancements (GLEs) are sudden and short-lived increases in cosmic rays intensities registered by neutron monitors and usually associated with powerful solar explosive events. This work examines the key features of forty-nine (49) Ground level enhancement (GLE) events with a view to understanding the possible link to their solar sources. These constitute the 22nd -71st GLE as recorded by the Oulu Neutron monitor. We have computed the increase rates of the GLE and have compared them with the associated solar activity parameters. It is observed that GLEs are more associated with Solar flares than CMEs during the minimum and ascending phase of the 11 year solar cycle when compared with GLEs that occurred during the maximum phase of the solar cycle. In general, more GLE events were associated with solar flares originating from the Northern hemisphere of the solar disk as compared with the southern hemisphere flares. 80% of GLE with percentage increase rate (PIR) <10% were linked with strong flares. There was no/weak statistical association between intensity of solar energetic events (solar flares, CMEs, etc) and increase rate of GLE. The harder solar energetic fluxes seem to be responsible for GLEs with high PIR and that the softer fluxes may be responsible for those with low PIR. These results have important implications for our present understanding of potential solar drivers of the GLEs.

Highlights

Ground level enhancement (GLE) are a consequence of the most energetic (~GeV) solar particles accelerated during solar explosive events such as flare processes and coronal mass ejections (CMEs)
For those with percentage increase rate (PIR) < 10%, we found that majority (78%) of the GLEs were associated with brighter flare, 9% were observed to associate with normal flare whereas, 13% GLEs were discovered to be associated with faint flare
For the events with PIR 10%, we found that majority (94%) of GLEs were associated with strong flare, while only 6% were observed to be associated with common flare

Summary

Introduction

Ground level enhancement (GLE) are a consequence of the most energetic (~GeV) solar particles accelerated during solar explosive events such as flare processes and CMEs. The primary cosmic rays initiate a complicated nuclearelectromagnetic –moun cascade in the atmosphere generating large variety of secondary particles resulting in an ionization of the ambient air. Impulsive SEP events without accompanying shocks and energetic storm particle events detected by spacecrafts near earth are concrete proof for the reality of flares and shock acceleration processes [14]. In addition both processes (SEP and flares) are expected to operate during major eruptions such as those involved in GLE events.

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