Demet Ulusen

Dynamical and magnetic field time constants for Titan's ionosphere: Empirical estimates and comparisons with Venus

plasma flow speed relative to the neutral gas speed is approximately 1 m s −1 near an altitude of 1000 km and 200 m s −1 at 1500 km. For comparison, the thermospheric neutral wind speed is about 100 m s −1 . The ionospheric plasma is strongly coupled to the neutrals below an altitude of about 1300 km. Transport, vertical or horizontal, becomes more important than chemistry in controlling ionospheric densities above about 1200–1500 km, depending on the ion species. Empirical estimates are used to demonstrate that the structure of the ionospheric magnetic field is determined by plasma transport (including neutral wind effects) for altitudes above about 1000 km and by magnetic diffusion at lower altitudes. The paper suggests that a velocity shear layer near 1300 km could exist at some locations and could affect the structure of the magnetic field. Both Hall and polarization electric field terms in the magnetic induction equation are shown to be locally important in controlling the structure of Titan’s ionospheric magnetic field. Comparisons are made between the ionospheric dynamics at Titan and at Venus.