Significant Enhancement of Turbulence Cascade Rates Downstream of Quasi–perpendicular Bow Shock at Mars

Compressible plasma turbulence is prevalent in planetary plasma environments. However, our current understanding of turbulence injection and dissipation in the highly-compressible magnetosheath is still quite limited. Previous studies have suggested that pickup ion instabilities originating from the far-extended neutral exospheres of Mars may contribute to energy injection, leading to the frequent observation of plateau-like spectral characteristics in the Martian magnetosheath. Nonetheless, it remains unclear how the turbulence cascade rates vary with local parameters related to the bow shock geometry and pickup ions. In this investigation, we conduct a joint analysis of Tianwen-1 and MAVEN data to unveil spectral characteristics and the varying turbulence cascade rates under different bow shock geometries. By employing the exact laws of compressible magnetohydrodynamics turbulence, we observe a systematic increase in cascade rates with the shock normal angle. As the geometry transitions from quasi-parallel to quasi-perpendicular, the ratio between the turbulence cascade rates of the upstream solar wind and the downstream magnetosheath increases by 20-30 times. Furthermore, we find that the turbulence cascade rate of cases exhibiting plateau-like spectral shapes increases more significantly with the shock normal angle compared to those without plateau-like features. Our findings offer new insights into understanding turbulence injection and dissipation downstream of collisionless super-critical bow shocks in space and astrophysical plasmas.