Martian Ionospheric Magnetic Fluctuations Below 200 km

We conduct a search for 5-16 Hz magnetic waves below 200 km and within the Martian ionosphere using data from multiple instruments onboard the Mars Atmosphere and Volatile EvolutioN mission spacecraft. We present a case study and an analysis of the 54 identified events to establish trends. Nearly half the wave events occur near the cusps of strong crustal magnetic fields (CMFs). The stronger regions have fewer events and may be a result of stronger CMFs preventing draped field lines from reaching lower altitudes. A majority of the observed magnetic waves occur on the nightside, are associated with greater fluxes of electrons traveling downward along the local magnetic field compared to those traveling upward, and correspond to increases in thermal plasma density. These aspects indicate electron precipitation was present during these wave events. We conclude that the waves are observed under magnetic field conditions favorable for the penetration of electrons and waves into the lower ionosphere, but that the electron precipitation cannot solely account for the waves or plasma changes.