The Impact and Mechanism of the Magnetic Inclination Angle on O⁺ Escape from Mars

Abstract

Ion escape from the atmosphere to space is one of the most likely reasons to account for the evolution of the Martian climate. Based on three-dimensional multifluid magnetohydrodynamic simulations, we investigated the impact of the magnetic inclination angle on O+ escape at low altitudes of 275–1000 km under the typical solar wind conditions. Numerical results showed that an outward ion velocity in the direction opposite to the electromagnetic (EM) force results in weak outward flux and leads to ions becoming trapped by the horizontal magnetic field lines at the local horizontal magnetic equator. Much of the EM force can be attributed to the Hall electric force. In the region of high absolute magnetic inclination angle, the outward ion velocity has the same direction as the EM force, which increases the outward flux and causes ions to diffuse upward along open magnetic field lines to higher altitude. In addition, the EM force is mainly provided by the electron pressure gradient force and the motional electric force. Global results for the magnetic inclination angle indicate that the strong crustal field regions in the southern hemisphere are mainly occupied by magnetic field lines with high absolute magnetic inclination angle, while horizontal field lines are dominant in the northern hemisphere, which leads to a higher O+ escape rate in the Martian southern hemisphere than in the northern, from altitudes of 275 to 1000 km. This is a significant advance in understanding the impact and mechanism of the Martian magnetic field directions on ion escape.

Influence of the Martian crustal magnetic fields on the Mars-solar wind interaction and plasma transport

“…Owing to the north-south asymmetry in the distribution of crustal fields on Mars, the magnetic structures also differ significantly between north and south. In the presence of strong crustal sources, enhanced closed and open fields occur in the southern hemisphere, which exert an influence even at high altitudes, controlling plasma motion and altering the position of the plasma boundary (Fang et al, 2017;Li et al, 2022a;Li et al, 2022b). In contrast, because of the lack of strong crustal fields in the northern hemisphere, the plasma environments are similar to those on unmagnetized planets, with the magnetic structure and plasma motion primarily controlled by the draped IMF.…”

“…Red/Blue points represent the case with/without the crustal fields. Frontiers in Astronomy and Space Sciences frontiersin.org magnetic field lines on the dayside may promote upward plasma motion and increase the ion loss rate (Li et al, 2022a), Table 1 indicates that the reduction in the global loss rate is strongly related to the reduction in the tailward flux.…”

“…As strong crustal field sources are primarily distributed in the Southern Hemisphere, the distribution of the magnetic topology presents an obvious north-south asymmetry. On the day, different magnetic field lines control the horizontal or radial plasma transport, altering the planetary ion escape rates and the location of the plasma boundaries (Matta et al, 2015;Dubinin et al, 2019;Li et al, 2022a). The plasma transport process is important in the ionosphere of Mars.…”

Effects of Force in the Martian Plasma Environment With Solar Wind Dynamic Pressure Enhancement

“…Also, the 1‐D neutral density profile used in S. Li et al. (2022), as shown in Figure 1a, has been adopted in our model as an initial input. Therefore, the influence of the asymmetric distribution of neutral density to Martian plasma environment is not included.…”

X-Ray Morphology Due to Charge-exchange Emissions Used to Study the Global Structure around Mars

“…The Navier-Stoker equations for each species are augmented by the interaction of electromagnetic effects. The physical detail for this 3D MHD model can be found in the studies of Li et al (2020Li et al ( , 2022.…”