First measurements of thermal tides in the summer mesopause region at Antarctic latitudes

1 We present the first detection of thermal tides in the middle atmosphere at polar latitudes in summer. The IAP iron lidar is in operation in Davis (69°S, 78°E), Antarctica, since December 2011 and measures temperatures in the height range 84–96 km with an accuracy of 1–3 K (after 1 hour integration) with an effective altitude resolution of 1 km. Iron densities are observed from ∼75–140 km. We analyze 171 hours of observations in the period 11–28 January, 2011, and find strong tidal modulations in Fe density and temperatures. Typical amplitudes of thermal tides are 2–4 K for both the diurnal and semidiurnal component. The diurnal tide is larger (smaller) than the semidiurnal component below (above) ∼90 km. The phase of the diurnal tide decreases with altitude by ∼1.3 h/km which corresponds to a vertical wavelength of ∼30 km. A similar phase progression is observed in Fe densities extending below and above the height range of temperature measurements. The overlay of diurnal and semidiurnal components leads to tidal modulations of up to ±6 K for temperatures, and up to ±4000/ccm (=±40%) for Fe number densities. These modulations are much larger compared to most simulations and point to some missing processes in tidal modeling.