Turbulence Properties of Corotating Interaction Regions at 1 AU: a Comprehensive Superposed Epoch Analysis

Abstract

We perform a comprehensive superposed epoch analysis (SEA) of more than 200 corotating interaction regions (CIRs) using WIND spacecraft observations at 1 AU. The stream interfaces are identified by Minimum Variance Analysis (MVA), and turbulence properties are evaluated using wavelet transforms over a wide range of temporal scales. The analysis of normalized cross helicity (${\sigma }_c$) and normalized residual energy (${\sigma }_r$) reveals distinct turbulence behaviors across frequencies. The spectral indices of both magnetic and velocity fluctuations smoothly transition from steeper in the slow wind to shallower in the fast wind, while a localized steepening of the velocity spectra near the interface indicates enhanced dissipation due to compression. Across broad frequency bands, ${\sigma }_c$ shows a clear dip at the stream interface, signifying increased inward Alfvén wave energy, whereas ${\sigma }_r$ displays a peak-valley-peak structure mainly driven by large-scale velocity shear. In lower-frequency ranges, velocity shear artificially enhances velocity fluctuation energy, producing strong peaks in ${\sigma }_r$, while higher-frequency ranges show a smooth increase of ${\sigma }_r$ from slow wind to fast wind. Nearly half of the analyzed CIRs are accompanied by a heliospheric current sheet (HCS), with many HCSs closely aligned with the stream interface, suggesting an intrinsic link between the two structures. Our findings offer valuable clues for reconciling discrepancies among earlier observational and simulation studies, and provide new insight into how compression and velocity shear modulate solar wind turbulence near CIRs.

arXiv comment15 pages, 9 figures, published on ApJ

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