The Dayside Ionosphere of Mars as Controlled by the Interplay Between Solar Wind Dynamic Pressure and Crustal Magnetic Field Strength

We investigate how the Martian dayside ionospheric structure is modified by crustal magnetic field (CMF) strength and upstream solar wind pressure by analyzing electron density data from the Langmuir Probe and Waves instrument onboard the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft. We find that the electron density above the exobase is anticorrelated with the ratio of solar wind's normal dynamic pressure (PSW perpendicular to ${P}_{\text{SW}\perp }$) to CMF magnetic pressure (PCMF ${P}_{\text{CMF}}$). We also analyze the electron density behavior across different magnetic topologies as a function of PSW perpendicular to/PCMF ${P}_{\text{SW}\perp }/{P}_{\text{CMF}}$. The extremely low electron density in the draped topology relates to ionopause-like structures. The lower electron density in the closed and open topology under higher PSW perpendicular to/PCMF ${P}_{\text{SW}\perp }/{P}_{\text{CMF}}$ may be attributed to a downward force, potentially the J x B force in the case of closed topology. This study highlights the complex interplay between solar wind and CMF in influencing the Martian dayside upper ionosphere.