Authors: Rubaiya Khondoker Shikha (Dept. of Space Science, UAH), Jakobus A. le Roux (Dept. of Space Science, UAH, CSPAR)

The acceleration and transport of solar energetic particles (SEPs) at quasi-perpendicular shocks frequently diverge from classical diffusion models, presenting a long-standing challenge in space physics. In this study, we investigated SEP dynamics at a 1 AU quasi-perpendicular shock detected by the ACE spacecraft on August 26, 1998 (Prete et al. 2021). To analyze this event, we applied a recently developed theory for tempered superdiffusive shock acceleration at perpendicular shocks (le Roux & Shikha, 2025), which effectively captures how particle transport transitions from superdiffusive to normal diffusive regimes near the shock boundary. By fitting the model’s analytical solutions to multi-channel SEP flux data, we identified clear signatures of superdiffusive transport. We found that the degree of superdiffusion increased at higher particle energies and, surprisingly, was more pronounced in the downstream region than upstream. To determine the physical cause of this behavior, we evaluated the statistical properties of the local magnetic field turbulence. We observed high kurtosis and heavy-tailed distributions on both sides of the shock, signaling intermittent, non-Gaussian turbulence; notably, this kurtosis was significantly higher downstream. This intensified downstream intermittency appears to drive the enhanced superdiffusive transport behind the shock. Furthermore, we mapped the specific spatial zones where SEP transport transitions back to normal diffusion, and used 2D vector plots of the magnetic topology to identify small-scale magnetic flux ropes. These coherent structures likely amplify turbulence and particle scattering, sustaining the superdiffusive transport observed on both sides. Ultimately, our results offer strong evidence for superdiffusive SEP transport at quasi-perpendicular shocks while establishing a clear link between particle propagation, turbulent intermittency, and embedded magnetic structures.