Search

The forecasting of solar energetic particles (SEPs) is a prominent area of space weather research. Numerous forecasting models exist that predict SEP event properties at proton energies <100MeV. One of these models is the SPARX system, a physics-based forecasting tool that calculates >10MeV and >60MeV flux profiles within minutes of a flare being detected. This work describes SPARX-H, the extension of SPARX to forecast SEP events above 300MeV . SPARX-H predicts fluxes in three high energy channels up to several hundred MeV. Correlations between SEP peak flux and peak intensity of the associated solar flare are seen to be weak at high energies, but improved when events are grouped based on the field polarity during the event. Initial results from this new high energy forecasting tool are presented here and the applications of high energy forecasts are discussed. Additionally, the new high energy version of SPARX is tested on a set of historic SEP events. We see that SPARX-H performs best when predicting peak fluxes from events with source locations in well-connected regions, where many large SEP events tend to originate., Comment: Accepted for publication in Space Weather 13 pages, 5 figures

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., Comment: ApJ accepted

Understanding the transport of Solar Energetic Particles (SEPs) from acceleration sites at the Sun into interplanetary space and to the Earth is an important question for forecasting space weather. The Interplanetary Magnetic Field (IMF), with two distinct polarities and a complex structure, governs energetic particle transport and drifts. We analyse for the first time the effect of a wavy Heliospheric Current Sheet (HCS) on the propagation of SEPs. We inject protons close to the Sun and propagate them by integrating fully 3D trajectories within the inner heliosphere in the presence of weak scattering. We model the HCS position using fits based on neutral lines of magnetic field source surface maps (SSMs). We map 1 au proton crossings, which show efficient transport in longitude via HCS, depending on the location of the injection region with respect to the HCS. For HCS tilt angles around $30^\circ-40^\circ$, we find significant qualitative differences between A+ and A$-$ configurations of the IMF, with stronger fluences along the HCS in the former case but with a distribution of particles across a wider range of longitudes and latitudes in the latter. We show how a wavy current sheet leads to longitudinally periodic enhancements in particle fluence. We show that for an A+ IMF configuration, a wavy HCS allows for more proton deceleration than a flat HCS. We find that A$-$ IMF configurations result in larger average fluences than A+ IMF configurations, due to a radial drift component at the current sheet., Comment: 16 pages, 8 figures and 1 table, plus appendix of 2 pages, 1 figure and 1 table

Solar Energetic Particles (SEPs), a major component of space weather, propagate through the interplanetary medium strongly guided by the Interplanetary Magnetic Field (IMF). In this work, we analyse the implications a flat Heliospheric Current Sheet (HCS) has on proton propagation from SEP release sites to the Earth. We simulate proton propagation by integrating fully 3-D trajectories near an analytically defined flat current sheet, collecting comprehensive statistics into histograms, fluence maps and virtual observer time profiles within an energy range of 1--800 MeV. We show that protons experience significant current sheet drift to distant longitudes, causing time profiles to exhibit multiple components, which are a potential source of confusing interpretation of observations. We find that variation of current sheet thickness within a realistic parameter range has little effect on particle propagation. We show that IMF configuration strongly affects deceleration of protons. We show that in our model, the presence of a flat equatorial HCS in the inner heliosphere limits the crossing of protons into the opposite hemisphere., Comment: 16 pages, 15 figures, accepted for publication in The Astrophysical Journal