| Popis: |
Understanding the properties and variability of the ionosphere is vital for understanding the atmosphere of Mars. The presence and property of waves provide insight into the plasma and magnetic environment. We conducted a search for 5 - 16 Hz signals below 400 km in magnetic field data from Mars Global Surveyor (MGS), the Mars Atmosphere and Volatile Evolution (MAVEN), and Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) missions. We discuss an analysis of 54 identified MAVEN events using multiple instruments and present a case study event. 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 these 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.We then discuss our null results regarding Schumann resonances, which are electromagnetic signals generated by lightning that, if they exist on Mars, are expected to propagate at 7-14 Hz. Future studies specifically looking for Schumann resonances will require higher sensitivity instruments and would benefit from additional missions that reach into the ionosphere of Mars. Finally, we comment on the inconsistency between identifying MGS events purely via by-eye analysis versus using quantitative methods for guidance. |
