Spatio‐Temporal Variability of Topside Layers in Mars’ Dayside Ionosphere Using Near‐Simultaneous Mars Express and MAVEN Conjunctions

Abstract This study investigates the spatio-temporal variability of topside ionospheric layers over the strong crustal magnetic fields and an unmagnetized region in the southern hemisphere of Mars with multipoint observations between Mars Express (MEX) and Mars Atmosphere and Volatile EvolutioN (MAVEN) very close in time and space. We identified 79 events between 2014 and 2021 when both spacecraft trajectories nearly overlapped. Four of these events, all from 2015 and in the dayside ionosphere, are selected: three occur over crustal field regions and one over an unmagnetized region. We analyze the ionosphere using radar sounding observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on MEX and compare them to in situ ionospheric measurements by the Langmuir Probe and Waves instrument on MAVEN. From across the four events of this study, a comparison of observations from both spacecraft shows the potential motion of topside ionospheric layers, which exhibited maximum displacements of 2.4 $2.4$° in latitude (149.4 km), 5.4° in east longitude (337.6 km), and up to 28 km in altitude over a span of 8–43 min. The electron densities of some of these structures increase by up to a factor of 2.6 during the same period of time. In this study, we demonstrate small and rapid variability occurring in the topside ionosphere of Mars, which was only possible to observe thanks to multispacecraft and near-simultaneous observations.