Tidal waves and ionosphere-thermosphere coupling at Mars

We present observations of non-migrating tidal wave perturbations in the ionosphere and thermosphere of Mars using in-situ measurements of electron and neutral atmosphere (CO₂+ O) densities made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite. The electron density is measured by MAVEN's Langmuir Probe and Waves (LPW) instrument and the neutral gas densities are measured by the Neutral Gas and Ion Mass Spectrometer (NGIMS). We focus on an interval from late February 2016 into April 2016 during which a good correlation between the ionospheric and thermospheric perturbations, corresponding to strong wavenumber 1, 3 and 4 tidal variations, are observed. During this interval, MAVEN's periapsis is located ~58^o- 69^onorth latitude, Mars solar longitude (Ls) is ~114^o- ~142^o(late northern summer into fall), over a range of local times, ~1 to ~12 LT, and solar zenith angles (SZA) from ~100^oto ~50^o. This study focuses on altitudes, ~150 to 300 km, which are above the peak electron density (~120 - 130 km), but covers the altitude over which diffusive transport processes start to dominate over photochemical processes (~200 km and above). Neutral density variations are compared to those in modeled neutral atmosphere densities from the Mars Climate Database (MCD), a database of statistics compiled from the Global Climate Model (GCM) simulations of the Martian atmosphere. Strong tidal variations are also present in the MCD model at this time along MAVEN's trajectory, and are reminiscent of those seen in the measured quantities. This study is motivated by the fact that such observations provide an opportunity to study the ionosphere thermosphere coupling process at Mars in the context and timescales of tidal dynamics.