Superposed Epoch Analysis of Stream Interaction Regions at 1 au During Solar Minimum With Turbulence Geometry Decomposition: Implications for Galactic Cosmic Ray Transport

Abstract In the inner heliosphere, stream interaction regions (SIR), where fast and slow solar wind streams meet, modulate the intensity of galactic cosmic rays (GCR) on the timescale of a few days. We perform a superposed epoch analysis (SEA) of solar wind, magnetic field, and high‐energy particle count rate data from the Advanced Composition Explorer to calculate the average bulk and turbulent features of SIRs associated with strong GCR depressions, as well as a mean percentage change profile for the galactic proton flux during these events. In particular, we split the power of nearly incompressible magnetic turbulence throughout the SIR epoch into the common slab and 2D modes, since these contribute to energetic particle diffusion in different directions relative to the background, time‐averaged field. We use the SEA results to compute parallel and perpendicular diffusion coefficients for GCRs during the passage of an average SIR and discuss our findings in the context of the particle observations and prior research. Our results suggest that GCR depletions through an SIR are primarily driven by a sharp decrease in the diffusion coefficients.