The Total Electron Content of the Martian Ionosphere From MRO/SHARAD Observations

The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter (MRO), used to search for subsurface water ice, requires corrections to range delays and image distortions caused by radiowave propagation through the Martian ionosphere. These corrections yield a phase parameter that is linearly correlated with values of the total electron content (TEC), defined as the integral of the electron density profile N-e(h). This new database has been validated using previous observational patterns of TEC magnitudes and variability versus latitude, local time, and season. The SHARAD TEC data span the years 2007 to 2014, providing the first opportunity to study solar cycle effects upon daytime TEC magnitudes. A parameterization of TEC versus solar zenith angle and solar flux, within the context of photochemical equilibrium theory, provides a flexible TEC module for the Mars Initial Reference Ionosphere (MIRI) model. A high spatial resolution study of TEC variability in the southern hemisphere confirmed a previously tentative conclusion about daytime TEC morphology controlled by the local inclination angles of crustal magnetic fields.