Influence of Crustal Magnetic Fields on Horizontal Plasma Transport and Ion Escape on Mars

Abstract

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 O _2 ^+ and CO _2 ^+ 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.

Keywords

• Mars
• Magnetohydrodynamical simulations
• Magnetic anomalies