EOMF-15. Surprising Results of Sensible Heat and Meteoric Na Fluxes in the Mesosphere and Lower Thermosphere Measured by Lidar at McMurdo, Antarctica
We report the first lidar observations of vertical fluxes of sensible heat and meteoric Na from 78-110 km in late May 2020 at McMurdo, Antarctica. The measurements include contributions from the complete temporal spectrum of gravity waves and demonstrate that wave-induced vertical transport associated with atmospheric mixing by non-breaking gravity waves, Stokes drift imparted by the wave spectrum, and perturbed chemistry of reactive species, can make significant contributions to constituent and heat transport in the mesosphere and lower thermosphere (MLT). A surprising discovery is the positive heat flux in the lower thermosphere (97-106 km), which contradicts conventional thinking but demonstrates the importance of the fully compressible solutions of polarization relations for mesoscale gravity waves. The measured sensible heat and Na fluxes exhibit downward peaks at 84 km that are lower by ~4 km than the peak fluxes observed at midlatitudes. This is likely caused by the strong downwelling over McMurdo in late May. The Na flux magnitude is double the maximum at midlatitudes, which we believe is related to strong inertial-period waves that are persistent in the MLT at McMurdo. To achieve good agreement between the measured Na flux and theory, it was necessary to assume that ~40% of gravity wave energy was propagating downward, especially between 80 and 90 km where the Na flux and wave dissipation were largest. These downward propagating waves are likely secondary waves generated in-situ by the dissipation of primary waves that originate from lower altitudes. The sensible heat flux transitions from downward below 90 km to upward from 97–106 km. The observations are explained with the fully compressible solutions for polarization relations of gravity waves dominated by mesoscale vertical wavelengths (λ_z>10 km).