The effects of atmospheric dust and solar radiation on the dayside ionosphere of Mars derived from 17 years of Mars Express radio science observations

This work combines 17 years of Mars Express radio science (MaRS) observations with proxies for insolation and local/global atmospheric dust to investigate the combined and individual effects on the dayside ionosphere of Mars from the top down to the ionospheric base. The increase in insolation from orbital apocenter to pericenter in combination with Mars‘ dust cycle causes an average rise of the whole photochemically dominated region of the dayside ionosphere, ranging from 13 km at the ionospheric base up to 22 km above the main peak during conditions without a global dust storm. The declining phase of the 2018 global dust storm was observed by MaRS on the southern hemisphere and close to pericenter. The observed lifting effect on the whole photochemically dominated region of the ionosphere from the increased insolation and the high local and global atmospheric dust levels exceeds that seen by MaRS from similar seasons during years without a global dust storm. The average ionospheric peak altitude at the subsolar point rises for increasing levels of local atmospheric dust until a maximum elevation is reached. This maximum depends on the available insolation at the top of the planetary atmosphere. Further increases of the local atmospheric dust levels do not lead to a further rise of the average ionospheric peak altitude in the investigated data set. This indicates a limit for the warming/expansion of the lower neutral atmosphere and the consecutive lifting of the ionosphere based on the available insolation and explains why regional dust storms can cause a similar lifting of the ionospheric main peak region as global dust storms. © 2023 Elsevier Inc. All rights reserved.
The Mars Express Radio Science Experiment (MaRS) was funded by BMWi Berlin via the Deutsches Zentrum für Luft- und Raumfahrt (DLR) under the Grant 50QM1802. Support for Mars Express Radio Science at Stanford University was provided by NASA through a JPL Contract. Support for the Multimission Radio Science Support Team was provided by NASA/JPL. Portions of this research were performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with NASA. We thank everyone involved in the Mars Express project at ESTEC, ESOC, ESAC, JPL, and the ESTRACK and DSN ground stations for their continuous support. K. P., M. P. and S. T. acknowledge funding for this project by the Deutsche Forschungsgemeinschaft (DFG) under Grant PE 3225/2-1, PA 525/25-1 and TE 664/4-1. F.G.G. acknowledges financial support from the grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033.