Perpendicular-Parallel Asymmetry of Venus Bow Shock Under Different Parker Spiral Angles

Several typical asymmetries in the Venusian bow shock (BS) location, including the magnetic north-south asymmetry, the pole-equator asymmetry, and the perpendicular-parallel asymmetry, have been proven to be controlled or affected by the interplanetary magnetic field (IMF) orientation. The physical reasons behind the perpendicular-parallel shock asymmetry remain inadequately explained. Effects of ion-scale dynamics have not been adequately addressed in both previous observational data and numerical simulations. Our newly developed multi-fluid Hall-MHD model, which incorporates the convection, Hall, and ambipolar electric fields in the ion transport and magnetic induction equations, effectively captures the ion-scale dynamic effects, providing a more comprehensive understanding of the underlying processes. The model self-consistently reproduce the plasma boundaries and regions of Venus at Parker spiral angle of 15°, 36°, and 90° . The simulation results show that the subsolar standoff distance and the asymmetry of bow shock are mainly dominated by the ambipolar and Hall electric fields. As the increase of Parker spiral angle, the ambipolar electric field weakens due to that the magnetic barrier becomes wider. And intensity of the Hall electric field is significantly enhanced to affect the structure of BS and eliminate the perpendicular-parallel asymmetry. There is also an obvious perpendicular-parallel asymmetry in energy transfer rate when the Parker spiral angle is less than 90°. Our findings highlight the necessity of incorporating ion-scale dynamics into the analysis of BS asymmetry changes, offering valuable insights into the complex interactions within space plasma environments.