Lidar observations of persistent gravity waves with periods of 3-10 h in the Antarctic middle and upper atmosphere at McMurdo (77.83°S, 166.67°E)

Persistent, dominant, and large-amplitude gravity waves with 3-10 h periods and vertical wavelengths ∼20-30 km are observed in temperatures from the stratosphere to lower thermosphere with an Fe Boltzmann lidar at McMurdo, Antarctica. These waves exhibit characteristics of inertia-gravity waves in case studies, yet they are extremely persistent and have been present during every lidar observation. We characterize these 3-10 h waves in the mesosphere and lower thermosphere using lidar temperature data in June from 2011 to 2015. A new method is applied to identify the major wave events from every lidar run longer than 12 h. A continuous 65 h lidar run on 28-30 June 2014 exhibits a 7.5 h wave spanning ∼60 h, and 6.5 h and 3.4 h waves spanning 40 and 45 h, respectively. Over the course of 5 years, 323 h of data in June reveal that the major wave periods occur in several groups centered from ∼3.5 to 7.5 h, with vertical phase speeds of 0.8-2 m/s. These 3-10 h waves possess more than half of the spectral energy for ∼93% of the time. A rigorous prewhitening, postcoloring technique is introduced for frequency power spectra investigation. The resulting spectral slopes are unusually steep (-2.7) below ∼100 km but gradually become shallower with increasing altitude, reaching about -1.6 at 110 km. Two-dimensional fast Fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20-30 km across periods of 3.5-10 h. These statistical features shed light on the wave source and pave the way for future research.