Comparison of the Ionospheric Dynamo Current of Mars Above InSight and Zhurong Landing Sites: A Modeling Study

Previous observational studies suggest that the surface time-varying magnetic field of Mars originates in large part from the dynamo currents in the Martian ionosphere. However, whether there are significant differences in the strength, configuration, diurnal, and seasonal variations of the dynamo currents above different regions need to be further studied. In this study, using the ionospheric parameters from Mars Climate Database version 5.3 (MCD v5.3) and 7 years of MAVEN magnetic field measurements, we compare the ionospheric dynamo currents above the landing sites of InSight (4.50 degrees N, 135.62 degrees E) and Zhurong (25.07 degrees N, 109.90 degrees E) and the resulting surface magnetic variations at the two landing sites by conducting a modeling study. We find that the average dynamo current as well as its diurnal magnetic field amplitude on the Martian surface is significantly stronger at InSight than that at Zhurong due to the stronger background magnetic field strength and more perpendicular angle between magnetic field and neutral wind vectors in the dynamo region, though the conductivities is always weaker over InSight landing site. The seasonal variation of the current intensity (represented by differences between northern winter and summer solstices) is prominent over InSight than that over Zhurong because the heliospheric distance effect-resulted conductivity difference is the dominate factor for the seasonal variations over InSight while both the heliospheric distance and solar zenith angle (SZA) contribute to the current intensity at different Ls over Zhurong. The two factors partially offset each other and lead to a smaller seasonal variation. The role of crustal field, as well as the latitude effects on dynamo currents is also discussed. This study provides an attempt to promote the understanding of the solar wind-induced magnetosphere-ionosphere-surface coupling process. Ionospheric dynamo current is the result of the coupling between solar wind-magnetosphere-ionosphere-atmosphere, and is one of the important sources of the time-varying magnetic field on the surface of the terrestrial planets such as Earth and Mars. Earth's ionospheric dynamo current, also known as Sq current, exhibits longitudinal, latitudinal, local time, and seasonal variations based on magnetic field measurements from large amount of the geomagnetic observatories and satellites. Unlike the Earth, InSight and Zhurong are the only two lander/rover, which can measure the surface magnetic field and reflect the Martian ionospheric dynamo current. It is suggestive to compare the differences of the dynamo currents and the resulting surface magnetic field at the two landing sites. Unfortunately, due to the limited exploration duration at each location (similar to 40 min), it is difficult to determine an accurate external magnetic field on the Martian surface from Zhurong magnetometer. Wind-driven dynamo current modeling is a powerful tool to investigate the difference in the dynamo current and surface magnetic field at the two landing sites. This study comprehensively investigates and compares the dynamo current intensities and seasonal variations, and the reasons for the differences between InSight and Zhurong landing sites. We compare the Martian ionospheric dynamo current over InSight and Zhurong landing sites through modeling The current and surface field are significantly stronger over InSight due to strong |B| and more perpendicular B-V angle Weaker seasonal variation appears at Zhurong due to offset between the heliospheric distance and solar zenith angle at solstices