Turbulence and Polytropic Changes across Interplanetary Shocks Observed by the Parker Solar Probe

Abstract Interplanetary shocks play a critical role in solar wind dynamics, influencing the properties of turbulence and thermodynamic processes. In this study, we statistically analyze changes in turbulence characteristics and polytropic indices across 37 quasi-perpendicular shocks observed by the Parker Solar Probe. By examining the power spectral densities of plasma and field fluctuations, we find that downstream fluctuation spectra in the inertial range are generally steeper and exhibit higher amplitudes than those upstream, indicating the generation and amplification of turbulence by interplanetary shocks. In contrast, changes in plasma cross helicity, residual energy, and relative density fluctuations across shocks depend on upstream fluctuation properties and tend to moderate the upstream states, suggesting a downstream mixing of different fluctuation modes driven by turbulence–shock interaction. Both compressible and incompressible turbulence cascade rates increase across shocks, with the increase being more significant for the compressible cascade rate. In addition, we find that the polytropic index is typically lower downstream of shocks, which is consistent with enhanced turbulent cascade rates and indicative of modified thermodynamic behavior associated with turbulent heating. These results provide new observational constraints on turbulence–shock coupling in the inner heliosphere and offer insights into the interpretation of shock jump conditions in turbulent solar wind environments.