Speaker: Dr. Dikshita Meggi (Leicester) Title: Martian ionospheric dynamics and the role of crustal magnetic fields Abstract: Mars, without a global dipole magnetic field, has its atmosphere directly exposed to the solar wind. Their interactions with remnant crustal magnetic fields of varying strength and inclination, mainly in the southern hemisphere, further complicate ionospheric dynamics. We exploit observations from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on Mars Express. Using selected orbits over strong crustal fields and unmagnetised regions spanning 12 years, two-dimensional maps of ionospheric variability quantifying electron density deviations from Chapman-layer behaviour are constructed. We find that topside layers are mostly confined to regions where crustal fields have horizontal inclinations or undergo drastic changes in orientation from vertical to horizontal. Spatio-temporal evolution of topside ionospheric features are then investigated using near-simultaneous observations during four MEX-MAVEN (Mars Express-Mars Atmosphere and Volatile EvolutioN) conjunctions, when both spacecraft trajectories nearly overlap in time and space. The analysed conjunction events show topside ionospheric variability, with topside layers varying in size and moving in space over 8-43 min, variability observable only through multi-spacecraft, near-simultaneous observations. Another MEX-MAVEN conjunction in the dayside ionosphere over strong crustal fields is also investigated, with MEX observing localised small-scale dynamics on short timescales of at most 7 seconds and spatial scales of a few tens of kilometres. Analysis of MAVEN magnetic field and plasma observations provides insight into the formation of this unique case with very patchy but intense ionization, suggesting that the internal structure of twisted crustal magnetic field lines may contribute to the observed ionospheric variability. Finally, current investigation focuses on ME

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