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As incident solar wind encounters the martian upper atmosphere, it undergoes deflection particularly in the magnetosheath. However, the plasma flow exhibits asymmetrical distribution features within this transition region, which is investigated by employing a three‐dimensional Hall magnetohydrodynamic (MHD) model from an energy transfer perspective in this study. Simulation results reveal that solar wind protons transfer momentum to ionospheric heavy ions through motional electric field in the hemisphere where the motional electric field points outward from the planet. In the opposite hemisphere, solar wind flow tends to be effectively accelerated by ambipolar and Hall electric fields. The distinct dynamics of solar wind protons in both hemispheres result in the asymmetrical deflection. Furthermore, the extent of asymmetry grows as the cross‐flow component of the upstream interplanetary magnetic field increases, but diminishes as the density of the solar wind proton increases, contingent upon the energy effectively acquired from ambipolar and Hall electric fields. Plain Language Summary: Due to the lack of a global intrinsic magnetic field at Mars, the solar wind has a direct interaction with the upper atmosphere of the planet. During this interaction, heavy ions from the martian ionosphere can be accelerated by the motional electric field of the solar wind, resulting in an excess of momentum in the martian system that necessitates the deflection of solar wind protons in the opposite direction to maintain balance. In this study, we utilize a Hall‐MHD model to study the asymmetrical deflection of the solar wind in the martian magnetosheath from an energy transfer perspective. Simulation results indicate that solar wind protons tend to effectively acquire energy from the ambipolar and Hall electric fields in the hemisphere opposite to the direction of the motional electric field and transfer its energy to heavy ions through the motional electric field in the opposite hemisphere, leading to an asymmetrical deflection of the solar wind. Furthermore, the degree of asymmetry is impacted by external solar wind conditions, including the strength of interplanetary magnetic field cross‐flow component and the density of solar wind protons. These findings provide valuable insights into the flow asymmetries that arise during the interaction between Mars and solar wind. Key Points: The multi‐fluid MHD model effectively reproduces the asymmetrical deflection of solar wind flow within the magnetosheathThe asymmetrical deflection of solar wind is a consequence of the discrepancy in energy transfer patterns between the two hemispheresThe impact of the strength of interplanetary magnetic field By and solar wind density on asymmetrical deflection is individually examined [ABSTRACT FROM AUTHOR]

Attributed to the lack of an Earth-like global intrinsic dipole magnetic field on Mars, the induced electromagnetic field environment plays a crucial role in the evolution of its atmosphere. The dominant motional electric field ( E M ) induced by the bulk motion of the magnetic field within the Martian magnetosheath serves to accelerate ions toward escape velocity, thereby forming a plume escape channel. However, the distribution morphology of E M itself has received limited attention in previous research. In this study, by taking advantage of the multi-fluid Hall-MHD model cooperating with the Martian crustal field model, we focus on elucidating the physical mechanisms underlying the asymmetrical distribution of E M and examining the influence of the crustal field on this asymmetry. The results obtained from the simulation conducted in the absence of the crustal field indicate that the E M is more intense within the − Z M S E magnetosheath, where E M is directed toward Mars, primarily due to its corresponding higher velocity and a stronger magnetic field at lower solar zenith angles. The Martian crustal field has the ability to enhance the local E M around the inner boundary of the magnetosheath by amplifying both the magnetic field and its associated velocity. Accordingly, these findings provide valuable insights into the asymmetric nature of E M within the Martian magnetosheath under typical quiet-time solar wind conditions. [ABSTRACT FROM AUTHOR]

As the interplanetary magnetic field (IMF) carried by the solar wind encounters the martian atmosphere, it tends to pile up and drape around the planet, forming looping magnetic fields and inducing marsward ion flows on the nightside. Previous statistical observations revealed asymmetrical distribution features within this morphology; however, the underlying physical mechanism remains unclear. In this study, utilizing a three‐dimensional multi‐fluid magnetohydrodynamic simulation model, we successfully reproduce the asymmetrical distributions of the looping magnetic fields and corresponding marsward flows on the martian nightside. Analyzing the magnetic forces resulting from the bending of the IMF over the polar area, we find that the asymmetry is guided by the orientation of the solar wind motional electric field (ESW). A higher solar wind velocity leads to enhanced magnetic forces, resulting in more tightly wrapped magnetic fields with an increased efficiency in accelerating flows as they approach closer to Mars. Plain Language Summary: As incident solar wind interacts with Mars, the entrained interplanetary magnetic field drapes and stretches around the planet. The draped fields are orientated in opposite directions on the east and west sides of Mars, resulting in magnetic reconnection, the formation of looping magnetic fields and induced marsward plasma flows on the nightside. Statistical observations suggest an asymmetric distribution of these structures, however, the underlying physical mechanisms for this asymmetry have not been determined due to limited spatial coverage offered by the single spacecraft investigations. In this study, by taking advantage of a Hall‐MHD model, we have successfully reproduced the asymmetrical distributions and elucidated the underlying mechanisms governing these morphologies. Simulation results demonstrate that magnetic forces tend to emerge around the polar region, which are determined by the orientation of the ESW, shifting the plasma flows and magnetic fields in the direction opposite to the motional electric field. A higher solar wind velocity condition will induce amplified magnetic forces, resulting in more tightly wrapped magnetic fields and an increase in the velocity of marsward flows closer to the martian nightside. These findings provide valuable insights into the influence of the ESW and solar wind velocity on the martian induced magnetosphere. Key Points: The asymmetrical distributions of looping magnetic fields and associated marsward flows can be well reproduced by a multi‐fluid magnetohydrodynamic (MHD) modelThe impacts of the motional electric field direction and the solar wind velocity on the asymmetries are investigated, respectivelyMagnetic forces shift the magnetic fields and marsward flows toward the direction opposite to the motional electric field [ABSTRACT FROM AUTHOR]

Solar wind dynamic pressure, consisting solar wind density nsw and velocity Vsw, is an important external driver that controls Martian plasma environment. In this study, a 3D magnetohydrodynamic model is applied to investigate the separate influences of solar wind density and velocity on the Martian ionosphere. The spatial distributions of ions in the dayside and near nightside ionosphere under different nsw and Vsw are analyzed, as well as the ion transport process. We find that for the same dynamic pressure condition, the ionosphere extends to higher altitudes under higher solar wind density, indicating that a solar wind velocity enhancement event is more efficient at compressing the Martian ionosphere. A higher Vsw will result in a stronger induced magnetic field, shielding the Martian ionosphere, preventing the penetration of solar wind particles. For the same dynamic pressure, increasing nsw (decreasing Vsw) leads to a higher horizontal ion velocity, facilitating day‐to‐night plasma transport. As a result, the ionosphere extends farther into the nightside. Also, the ion outflow flux is larger for high nsw, which may lead to a higher escape rate. Moreover, the strong crustal fields in the southern hemisphere also cause significant effect to the ionosphere, hindering horizontal ion transport. An additional outflow channel is also provided by the crustal field on the southern dayside, causing different responses of flow pattern between local and global scale while the solar wind condition is varied. Plain Language Summary: Solar wind dynamic pressure is one of the main factors that influence Martian space environment. Variation in solar wind velocity and density can cause different effects to the magnetic field and plasma environment in Martian space. By using time dependent 3D multifluid MHD model, we studied the influence of individual solar wind velocity and density on the Martian ionosphere and plasma flow. We found that a higher solar wind density can cause an expansion of ionosphere and a higher outward flow of ions, while a higher solar wind velocity can decrease the horizontal ion velocity and day‐to‐night transport by enhancing the strength of induced magnetic field, thus the ionosphere extends farther into the nightside under low solar wind velocity condition. The remnant fields of Mars also cause an apparent north‐south asymmetry in the ionosphere, since strong crustal fields can deflect plasma flow, hindering horizontal plasma transport while providing an additional vertical outflow channel. Key Points: For constant solar wind pressure, the Martian ionosphere compresses as the solar wind velocity increasesFor constant dynamic pressure, higher solar wind density leads to higher horizontal ion velocity, facilitating day‐to‐night transportStrong remnant fields in the southern hemisphere uplift the Martian ionosphere and hinder horizontal ion transport [ABSTRACT FROM AUTHOR]

Owing to its unevenly distributed crustal fields, Mars acts as a unique obstacle to the solar wind. In the presence of the crustal fields, the transport of the planetary ions on the dayside ionosphere exhibits north–south asymmetry. Additionally, the heavy-ion loss in the magnetotail is affected by the crustal fields. In this paper, a three-dimensional multispecies magnetohydrodynamic model is employed to simulate Mars–solar wind interactions. Numerical results indicate that the meridional transport is dominant in most areas on the dayside ionosphere. In the presence of the crustal fields, the meridional transport on the southern hemisphere (southward transport) is reduced by more than 70% above the strong crustal sources, and the zonal velocity shows local changes inside strong and weak crustal field regions. These effects result in an increase or decrease in the number density of the heavy ions reaching the terminator, thereby influencing the thickness of the ionosphere. Decreased southward velocity leads to a reduction in the heavy-ion loss on the southern magnetotail. The radial outward flux is reduced by more than 30% for O2+ and CO2+ and by 10% for O+. This study shows that in addition to the zonal transport, the meridional transport is important for the day-to-night transport on the dayside of Mars. Collectively, the horizontal plasma transport, controlled by crustal fields, is associated with the altered ionosphere structure and reduced heavy-ion loss in the magnetotail. [ABSTRACT FROM AUTHOR]