Deflection of O₂ ⁺ Ion Flow by Magnetic Fields in the Martian Ionosphere

Abstract

The effect of the Martian crustal magnetic field on ion escape is the focus of considerable interest. Directions of magnetic fields near Mars determined by the interaction between Mars’ crustal and interplanetary magnetic fields have been suggested to play a significant role on ion transport around Mars. In this study we investigate the physical mechanism of deflection of O 2 + ion flow in two typical magnetic field orientations at the horizontal plane in the Martian ionosphere by performing 3D multifluid Hall magnetohydrodynamic simulations. Cross validation of the simulation results from two cases with the G110 crustal field model and equivalent source dipole model reveals that due to the Hall electric force, O 2 + ion flow tends to be accelerated eastwards in the region occupied by outward magnetic fields, and westwards in the region with inward magnetic fields. These results are helpful for understanding the impact of magnetic fields on the deflection of ionospheric ions in the Martian space environment.

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

“…In the presence of the crustal fields, the southward velocity (blue solid line) is reduced from a maximum of 8.1 km s −1 to an average value of 2 km s −1 in the southern hemisphere. This result indicates that the strong crustal source may inhibit the meridional transport and lead to the deflection of the plasma flow (Li et al 2022b). At an altitude of 500 km, the peak value 8 km s −1 of V θ at approximately (40°S, 180°W) agrees well with the numerical results reported by Liemohn et al (2017).…”

“…However, compared with the obvious relationship between V θ and the crustal field strength, the relationship between V j and the crustal field strength remains unclear. Above the altitude of 200 km, several probable mechanisms drive and influence the horizontal motion of the heavy ions, such as plasma pressure and magnetic pressure gradients (Chaufray et al 2014;Wu et al 2019), Hall electric force (Li et al 2022b), vertical and close magnetic topology near the strong crustal fields (Matta et al 2015;Wu et al 2019), and large ballistic flows along closed loops connecting day and night (Xu et al 2017a(Xu et al , 2017bWeber et al 2017). Moreover, on Venus, the momentum transfer from the solar wind is generally considered important for the ionospheric flow (Pérez-de-Tejada et al 2013).…”

“…However, local crustal magnetic fields, primarily distributed in the southern hemisphere, exert complex influence on the Marssolar wind interaction (Acuña et al 1998;Connerney et al 2005;Liemohn et al 2006;Brain et al 2007;Ma et al 2014;Xu et al 2014;Dong et al 2015), altering plasma boundary locations (Brain et al 2005;Edberg et al 2008;Xu et al 2016;Fang et al 2017). Additionally, the local crustal magnetic fields inhibit or promote the process of plasma transport (Brain et al 2006;Cao et al 2019;Li et al 2022aLi et al , 2022b.…”

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

“…Published studies have indicated that strong crustal field sources provide enhanced magnetic pressure on the dayside ionosphere, counterbalancing the forces exerted by the solar wind plasma and protecting planetary ions from the solar wind (Crider and Dana., 2002;Bertucci et al, 2003;Fang et al, 2015). Previous studies have discussed the variation in dayside radial transport under the influence of crustal fields and the influence on plasma escape (Matta et al, 2015;Li et al, 2022a;Li et al, 2022b). This study demonstrates that when the strongest crustal source faces the Sun, the shielding effect forces the planetary ions to remain in the middle-SZA areas (Lundin et al, 2011;Dubinin et al, 2019;Fowler et al, 2022).…”

“…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.…”