Shock and SEP Modeling Study for the 5 September 2022 SEP Event

TL;DR

This study combines observational data and advanced modeling to analyze the shock wave and SEP event on September 5, 2022, revealing delayed SEP onset, the role of shock flank acceleration, and minimal cross-field diffusion effects.

Contribution

It introduces a data-driven SEP simulation that accurately reproduces observed SEP features and clarifies the physical processes behind SEP acceleration and release during the event.

Findings

SEP onset delay explained by shock flank acceleration

Simulation reproduces energy spectrum and IVD observations

Cross-field diffusion has minor impact on SEP propagation

Abstract

On September 5, 2022, during Parker Solar Probe's (PSP) 13th encounter, a fast shock wave and a related solar energetic particle (SEP) event were observed as the spacecraft approached the perihelion of its orbit. Observations from the Integrated Science Investigation of the Sun (ISOIS) instrument suite show that SEPs arrived at the spacecraft with a significant delay from the onset of the parent solar eruption and that the first arriving SEPs exhibited an Inverse Velocity Dispersion (IVD) for energetic protons above $\sim$1~MeV. Utilizing data from multiple spacecraft we investigate the eruption dynamics and shock wave propagation. Our analysis includes 3D shock modeling and SEP transport simulations to examine the origins of this SEP event and explore the causes of the delayed SEP onset and the observed IVD. The data-driven SEP simulation reproduces the SEP event onset observed at PSP, its evolving energy spectrum and the IVD. This IVD is attributed to a relatively slow, ongoing particle acceleration process occurring at the flank of the expanding shock wave intercepted by PSP. This has significant implications for the role of shocks in the release of SEPs at widespread events and for methods used to infer the SEP release times. Furthermore, the match between the simulation and observations worsens when cross-field diffusion is considered, indicating that SEP diffusion had a minor effect on this event. These findings underscore the complexity of SEP events and emphasize the need for advanced modelling approaches to better understand the role of shock waves and other physical processes in SEP acceleration and release.