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

Creators: Alonso Guzmán, J. G.¹; Ghanbari, K.^{1, 2}; Florinski, V. A.^{1, 2}; Leske, R. A.³; Zhao, L.‐L.^{1, 2}; Zhu, X.²; Silwal, A.¹; Subashchandar, N. S. M.¹

1. University of Alabama in Huntsville
2. Center for Space Plasma and Aeronomic Research, Huntsville, AL, USA
3. California Institute of Technology

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.

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Acknowledgement

J.G.A.G. is supported by NASA Grant 80NSSC24K0568. V.A.F. acknowledges support from NASA Grant 80NSSC20K0786 and NSF Grant 2009871. R.A.L. acknowledges support from NASA Grant 80NSSC23K0543. L.Z., X.Z., A.S., and N.S.M.S. acknowledge partial support by NASA awards 80NSSC20K1783 and 80NSSC23K0415. A.S. is partially supported by NASA Grant 80NSSC24K1867. J.G.A.G would like to thank Swati Sharma for her prompt and generous responses to his frequent requests for literature review material.

Data Availability

We obtained our data for instruments onboard the ACE directly from the ACE Science Center (https://izw1.caltech.edu/ACE/ASC/index.html). For the solar wind bulk quantities, we used 64s Level 2 (Verified) data from the Magnetic Field Experiment (MAG) (C. Smith et al., 1998) and the Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) (McComas et al., 1998) instruments. For the cosmic rays, we used 1-hr Level 3 (Contributed) data from the CRIS (Stone et al., 1998) instrument. Specifically, at the time of submission of this manuscript, it is the first entry under the category “Cosmic rays, Particle fluences, other Items.” The code used to perform the data analysis (Alonso Guzman, 2025) is freely available on GitHub (https://github.com/jgaloguz/SIR-analysis-tools).

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JGR Space Physics - 2025 - Alonso Guzmán - Superposed Epoch Analysis of Stream Interaction Regions at 1 au During Solar.pdf

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