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

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. Plain Language Summary: Around Earth, the movement of high‐energy particles coming from outside of our solar system is significantly influenced by structures of plasma flowing from the Sun in regions where faster, hotter flows catch up to slower, denser streams. We perform a statistical analysis of spacecraft data to find the average profile of various large and small scale quantities around these structures. In particular, we study the turbulence, that is, the mechanism by which large‐scale waves transfer energy to small‐scale fluctuations in a fluid, as a function of time within these structures by assessing the relative contribution to the total magnetic turbulent energy from the two most common types of turbulence found in space plasmas near Earth. With the information we obtain, we can estimate how quickly the energetic particles diffuse through these structures along different directions and evaluate the validity of several theories regarding their movement during these events. Our findings support the idea that the intensity reduction of very high‐energy charged particles measured through the structures can be explained by the change in diffusion properties. Key Points: During solar minimum, galactic cosmic rays (GCR) are primarily modulated by stream interaction regions (SIR) in the inner heliosphereThrough a superposed epoch analysis, we characterize the bulk and turbulent properties of SIRs associated with strong GCR depressionsWe find a significant decrease in the diffusion coefficients at and through the interface between slow and fast streams [ABSTRACT FROM AUTHOR]