Deflection of Global Ion Flow by the Martian Crustal Magnetic Fields

Without the protection of a global magnetic field, erosion of the Martian ionosphere by the solar wind leads to abundant loss of atmospheric particles. Although the crustal magnetic fields in the Martian southern hemisphere are strong enough to affect the dayside-induced magnetosphere, there is still limited evidence for the deflection of the solar winds by the crustal magnetic fields. With 4 years of ion data measured by the Mars Atmosphere and Volatile EvolutioN mission, we investigate the flow pattern of protons, O⁺, and ${O_2}^{+}$ when the crustal fields rotate to different local times. Our result is the first evidence that suggests the crustal magnetic fields can withstand the solar wind flows on the Martian dayside and can effectively trap heavy ions below 1000 km. The gyroradii of heavy ions in the strong crustal fields regions are one order of magnitude smaller than in other regions. The trapping effect causes different flow patterns, while the crustal fields rotate to different subsolar regions but are attenuated at higher altitudes. Observations provide essential information to investigate the effect of the crustal magnetic fields on heavy-ion flows and understand the role of the crustal magnetic fields in the interaction between the solar wind and the Martian atmosphere.