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 orientation. The physical reasons behind the perpendicular-parallel shock asymmetry remain inadequately explained. The effects of ion-scale dynamics have not been adequately addressed in both previous observational data and numerical simulations. Using global multifluid simulations, we demonstrate that the electric field strength differs significantly between the two types of BS, resulting in their asymmetric positions relative to the planet. The quasi-perpendicular BS generates a stronger Hall electric field, which decelerates the solar wind at a greater distance from Venus. In contrast, the weaker electric field at the quasi-parallel BS only effectively slows down the solar wind closer to the planet, leading to further compression of the induced magnetosphere and an enhanced ambipolar electric field due to increased electron pressure gradients. The differential energy transfer from the solar wind at the two BS types contributes to the asymmetry in plasma flow and magnetic field accumulation downstream. These findings provide new insights into the plasma dynamics around unmagnetized planets and highlight the role of electric field structure in shaping the induced magnetosphere of Venus.