Spatial Variability and Correlation Lengths Within Stream Interaction Regions at 1 au: Comparison Between ACE and Wind

Abstract Understanding the spatial variability and correlation lengths throughout Stream Interaction Regions (SIRs) has importance both for fundamentally understanding the structuring of the solar wind and SIRs and for space weather operations. SIR observations from Advanced Composition Explorer and Wind are utilized to characterize the spatial variability of these structures and to compute correlation lengths of the solar wind speed and magnetic field magnitude for different regions of the SIR. In general, the probability of agreement between time‐shifted magnetic field magnitudes and solar wind speeds decreases with increasing spacecraft separation, with this degradation being more pronounced in the magnetic field magnitude. While the slow compressed region of the SIR has the steepest decline in agreement for the magnetic field magnitude, it is the shallowest decline for the percent agreement of solar wind speed. Despite these trends, the correlation length is longest in the slow compressed region for both magnetic field magnitude and solar wind speed, with the magnetic field magnitude generally having a longer correlation length than speed. These findings are consistent with current sheet layering within the compressed regions of the SIR and impacts of large‐amplitude Alfvénic fluctuations within the compressed and pristine fast solar wind. These results also further demonstrate the limitations of treating structures in the solar wind as laminar slabs, rather than being highly structured and variable, which may have impacts on uncertainties in space weather forecasting.