Forecasting SEP Events During Solar Cycles 23 and 24 Using Interpretable Machine Learning

ABSTRACT Prediction of the Solar Energetic Particle (SEP) events garner increasing interest as space missions extend beyond Earth's protective magnetosphere. These events, which are, in most cases, products of magnetic reconnection-driven processes during solar flares or fast coronal-mass-ejection-driven shock waves, pose significant radiation hazards to aviation, space-based electronics, and particularly, space exploration. In this work, we utilize the recently developed dataset that combines the Solar Dynamics Observatory/Helioseismic and Magnetic Imager's (SDO/HMI) Space weather HMI Active Region Patches (SHARP) and the Solar and Heliospheric Observatory/Michelson Doppler Imager's (SoHO/MDI) Space Weather MDI Active Region Patches (SMARP). We employ a suite of machine learning strategies, including Support Vector Machines (SVM) and regression models, to evaluate the predictive potential of this new data product for a forecast of post-solar flare SEP events. Our study indicates that despite the augmented volume of data, the prediction accuracy reaches 0.7 0.1, which aligns with but does not exceed these published benchmarks. A linear SVM model with training and testing configurations that mimic an operational setting (positive-negative imbalance) reveals a slight increase (+0.04 0.05) in the accuracy of a 14-hour SEP forecast compared to previous studies. This outcome emphasizes the imperative for more sophisticated, physics-informed models to better understand the underlying processes leading to SEP events. INTRODUCTION Solar Energetic Particle (SEP) events are one of the manifestations of solar activity that may significantly impact the conditions of the space environment. For example, the large solar particle event of September 2017 emphasized a significant surge in the charged and neutral particle flux that was able to reach Mars' surface (Zeitlin et al. 2018). While the doses from this specific event were below NASA's stipulated radiation exposure limits for astronauts, the risk for future explorers is evident. This concern becomes particularly relevant in scenarios where human explorers might be far from their habitats on other celestial bodies, with the onset of an event leaving them vulnerable to enhanced radiation doses. Therefore, forecasting and predicting SEP events is paramount. SEP events vary in intensity, spanning from suprathermal (few keV) up to relativistic (few GeV) energies, and are accelerated near the Sun either by magnetic reconnection-driven processes during solar flares or by fast Coronal Mass Ejections (CME).