Modelling the transport of relativistic solar protons along a heliospheric current sheet during historic GLE events

TL;DR

This study uses 3D simulations to investigate how the heliospheric current sheet influences the transport of relativistic solar protons during historic GLE events, improving understanding and modeling of these high-energy phenomena.

Contribution

The paper introduces a 3D test particle simulation approach focusing on the HCS's role in GLE proton transport, highlighting its significance in 71% of analyzed events.

Findings

Active regions near the HCS are more likely to produce GLEs.

The HCS significantly influences proton transport and observed intensities.

Including the HCS improves the accuracy of GLE intensity models.

Abstract

There are many difficulties associated with forecasting high-energy solar particle events at Earth. One issue is understanding why some large solar eruptive events trigger ground level enhancement (GLE) events and others do not. In this work we perform 3D test particle simulations of a set of historic GLEs to understand more about what causes these powerful events. Particular focus is given to studying how the heliospheric current sheet (HCS) affects high-energy proton transport through the heliosphere following an event. Analysis of $\geq$M7.0 flares between 1976$-$2020 shows that active regions located closer to the HCS ($<$10$^{\circ}$) are more likely to be associated with a GLE event. We found that modelled GLE events where the source region was close to the HCS also led to increased heliospheric transport in longitude and higher count rates (when the Earth was located in the drift direction). In a model that does not include perpendicular diffusion associated with turbulence, the HCS is the dominant mechanism affecting heliospheric particle transport for GLE 42 and 69, and varying other parameters (e.g. a narrow, 10$^{\circ}$, or wider, 60$^{\circ}$, injection width) causes little change. Overall in our model, the HCS is relevant in 71$\%$ of our analysed GLEs and including it more accurately reproduces observed intensities near Earth. Our simulations enable us to produce model profiles at Earth that can be compared to existing observations by the GOES satellites and neutron monitors, as well as for use in developing future forecasting models.