Abstract

Based on the data of Maven's NGISM neutral composition and Langmuir probe electron density and temperature, we statistically analyzed the climatic variations of the Martian thermosphere and ionosphere, and found significant north-south asymmetry. In winter and summer, it mainly comes from the north-south asymmetry of solar zenith Angle. The observational data still show significant north-south asymmetry in equinox seasons. Under low solar EUV radiation, the thermosphere density in the northern hemisphere is higher than that in the southern hemisphere. With solar radiation increase, the thermosphere density in the southern hemisphere gradually exceeds that in the northern hemisphere. In addition, the southern hemisphere increases non-linearly with the increase of solar radiation, while the northern hemisphere increases linearly. The electron density in Martian ionosphere also shows significant north-south asymmetry in seasons. The electron density in the southern hemisphere is higher than that in the northern, and the electron temperature in the southern hemisphere is lower than that in the northern. The asymmetries in the ionosphere and thermosphere between the northern and southern hemispheres are likely related to significant differences in Mars' north-south topography or to north-south asymmetries in the residual magnetic field. After preliminary analysis, we found that the north-south asymmetry of Mars' remaining magnetic field would intensify the hemispheric asymmetry of the ionospheric electron density, but have no effect on the thermospheric neutral density. The hemispheric asymmetry may be mainly related to the significant difference in Mars' north-south topography.