A Statistical Study of the Vertical Scale Height of the Martian Ionosphere Using MAVEN Observations

The Vertical Scale Height (VSH) is a crucial parameter that describes the shape of the ionospheric electron density profile. Evidence suggests a complex relationship between VSH and the thermal structure and dynamics of the ionosphere. A statistical study was conducted on the VSH at low altitudes (175 km) and high altitudes (300 km) in the Martian ionosphere, using data from the MAVEN observations from 2014 to 2023. The results suggest that the influence of the crustal magnetic field on VSH175 is more pronounced than on VSH300. VSH175 shows a minor peak around -20 degrees latitudes, which is more than 7% higher than the average value, and an increasing trend with latitude in the northern hemisphere. VSH300 is higher in the southern hemisphere than in the northern hemisphere, especially in summer, by approximately 42.1%. Regarding the local time variation of VSH, we observed an increasing trend from midnight to morning and a decreasing trend from dusk to midnight in almost all conditions. The local time variation of VSH also exhibits seasonal and latitudinal dependence. These variations have different levels of consistency with the gradient of the electron temperature (Te) and the collision frequency between charged particles and neutrals. Specifically, the correlation coefficient between VSH175 and the collision frequency between charged particles and neutrals reaches as high as 0.93 in the northern hemisphere winter and southern hemisphere summer. The correlation coefficient between VSH300 and the gradient of the Te reaches up to 0.72 in the southern hemisphere equinox. The ionosphere is produced by photo-ionization of the Martian upper atmosphere. The Vertical Scale Height (VSH) is a parameter that describes how quickly the electron density in the ionosphere changes with height. It is closely linked to the thermal structure and dynamics of the ionosphere. Our research focuses on how the crustal magnetic field affects the VSH on Mars and looks at variations with latitude and local time at low altitudes (175 km) and high altitudes (300 km) using MAVEN observations. We find that high VSH values at 175 km align with areas of strong crustal magnetic fields on Mars. There are significant latitudinal and daily variations in the VSH of the Martian ionosphere. Latitudinal variation is mainly manifested as hemispherical asymmetry, which may be related to Martian topography. The daily variations are influenced by the temperature gradient and the collision frequency between charged particles and neutrals. These effects also have dependences on altitude and season. The crustal magnetic field of Mars has a significant effect on Vertical Scale Height (VSH) at low altitudes Our analysis revealed evident diurnal and latitudinal variations in the VSH of the Martian ionosphere The thermal structure and dynamics contribute differently to local time variation of the VSH at different heights