Evolution of Solar-Wind Turbulence Correlation Lengths Across Interplanetary Shocks

Despite decades of study, questions about particle acceleration and energy cascades within the heliosphere remain open. Understanding these turbulent processes is key to understanding solar wind plasma dynamics. Interplanetary shocks provide a natural laboratory for investigating turbulent properties across the shock in upstream and downstream regions. However, conventional single-point spacecraft observations make it difficult to distinguish spatial from temporal variations, limiting direct comparisons with theoretical models.

We used the Wind, ACE, and DSCOVR missions, which are located at the L1 Lagrange point, to study turbulent scales perpendicular and parallel to the interplanetary (IP) shock normal. We estimate correlation lengths and effective Reynold numbers from the autocorrelation functions (ACFs). We show that these turbulent parameters decrease from upstream to downstream. However, an extended statistical analysis of tens of IP shocks showed little or no systematic decrease in correlation length across shocks. This can be related to the limitations of single-point measurements and to the small upstream and downstream intervals for the estimation of ACFs. To partially overcome these limitations, we identified cases in which the same turbulent structures were first observed upstream by Wind and then downstream by MMS near the subsolar point. This enabled us to better compare the properties of turbulence across the Earth’s bow shock. This multi-spacecraft configuration improves constraint on the spatial evolution of turbulence across shocks, allowing for more reliable estimates of correlation scales.