Authors: Xiaohan Ma (BU), Lingling Zhao (UAH), Merav Opher(BU)

The shape and structure of the heliosphere remain subjects of ongoing debate, particularly regarding the extent of heliospheric jets and their role in generating turbulence within the heliosheath (HS). In this work, we perform power spectral density (PSD) and intermittency analyses using long-term magnetohydrodynamic (MHD) simulations to investigate the multiscale dynamics associated with co-evolving Rayleigh–Taylor (RT) and Kelvin–Helmholtz (KH) instabilities. The results reveal distinct scale-dependent spectral regimes linked to the nonlinear evolution of these instabilities. At large scales (>60–100 AU), the spectra are dominated by instability-driven structures and exhibit a pronounced spectral enhancement consistent with direct energy injection from large-scale KH waves and vortical motions. At scales of approximately 30–60 AU, the spectral index approaches a Kolmogorov-like −5/3 scaling, suggesting the development of an inertial-like range. At scales 12-24 AU, the spectra display quasi-periodic temporal variations, indicating modulation by coherent structures associated with the instability cycles. At small scales 6–12 AU, the spectra flatten again toward a −5/3 slope, consistent with the emergence of renewed turbulent-like fluctuations produced by the fragmentation and nonlinear evolution of intermediate-scale structures. Scale-dependent flatness analysis further identifies intermittent behavior (F > 3) below ~35 AU, with intermittent enhancements occurring preferentially during periods of strong RT/KH activity. Together, these results suggest that energy injected by large-scale HS instabilities is redistributed across scales through the nonlinear evolution and fragmentation of coherent structures, contributing to the development of turbulence in the heliotail.