2:00 PM - 2:15 PM
[PCG25-12] Global characterization of wave perturbations in the middle atmosphere on Mars
Keywords:Mars, mesosphere, thermosphere, waves, tides
In order to clarify a global characteristic of waves and its upward propagating processes, we use IUVS stellar occultation measurements to characterize a global distribution of waves in the middle atmosphere between 24 March 2015 and 12 April 2018 for two Martian Years. This study first revealed global characteristics of wave perturbations in the night side temperature profiles derived from MAVEN/IUVS stellar occultations at 20 - 160 km altitudes on Mars. The peak amplitudes of waves on Mars exceed 20 % which is larger than those in Earth’s mesosphere/thermosphere (~5-13 %). Perturbations were found to be notably large in summer hemisphere at Ls = 0-180. These waves can be interpreted as resulting from superposed harmonics of internal gravity waves and thermal tides. The superposition of thermal-tides and small-scale perturbations generate extensive instability layer around 70 - 100 km, which potentially causes wave-breaking and turbulences. Vertical wavenumber spectral density in the Martian middle atmosphere shows a power-law dependence with the logarithmic spectral slope of -3. This is similar to the features seen in the Earth’s atmosphere. The spectral density in southern hemisphere at Ls = 225-315 tends to follow the semi-empirical spectrum of saturated gravity waves on the high-wavenumber side. The spectral power at high-wavenumbers is lower at 80 - 160 km than that at 20 - 80 km. This suggests that the strong radiative damping by CO2 15-micron could effectively dissipates shorter waves. Instead, the spectral power at low-wavenumbers suggests the amplitude growth with height of unsaturated waves toward upper thermosphere.