The global dust storms on Mars usually have significant influences on its atmosphere and ionosphere. However, the effects of dust storms on the Martian upper ionosphere are still unclear, especially in observations. In this research, the behavior of O2+, CO2+, and O+ density profiles during the 2018 global dust storm is studied based on the observations of NGIMS onboard MAVEN. The observations show increased CO2+ density, decreased O+ density, and relatively stable O2+ density at 170 km – 500 km during the dust storm, which must be the combined effects of latitude, longitude, season, local time and the dust storm. The decrease of O+ density seems to be a sudden process related to the global atmospheric circulation changes. The observations also show that the strong crustal magnetic field in the southern hemisphere might be able to promote the increase of CO2+ density above 300 km during the dust storm. Using a photochemical model, we reproduced the observed behavior of O2+, CO2+, and O+ density at 170 km to 200 km during the dust storm based on the variations of CO2 and O density profiles. With the help of MCD, the effects of latitude, longitude, season, and local time on neutral atmosphere and ionosphere are removed. Our results show a dust storm influence of O+ density decrease of ~50%, CO2+ density increase of ~100-300%, and O2+ density increase of ~50% at 170 km - 200 km. The results are consistent with the results of Fang et al. [2020].
 

Martian ionosphere; Martian dust storm; Photochemical equilibrium