PhD defence of Mohamed Mossad: Gravity Wave Spectra, Variability, and Interactions in the Middle Atmosphere Using Doppler Lidar Observations

Abstract:

Atmospheric gravity waves (GWs) transport energy and momentum into the middle atmosphere, where their dissipation drives the large-scale circulation. Yet their energy spectra are hard to quantify from gappy, noisy observations. This cumulative thesis characterizes GW spectra, variability and wave–mean-flow interactions at 30–70 km altitude using simultaneous temperature and wind profiles from the Doppler Rayleigh-Mie-Raman lidars at ALOMAR (69°N) and Kühlungsborn (54°N). 

Benchmarks with synthetic data show that interpolation-based Fourier spectra artificially steepen spectral slopes, whereas the Haar structure function and the uncertainty-weighted generalized Lomb–Scargle periodogram are far less biased. Applying these methods to seven years of ALOMAR soundings (2017–2023) yielded the first multi-year study of GW kinetic and potential energy spectra in the polar middle atmosphere. Winter shows broadband wave activity, whereas summer spectra exhibit broken power laws and a distinct population of near-inertial waves. The kinetic-to-potential energy ratio rises to about 20 at short vertical wavelengths, so temperature-only measurements underestimate the total GW energy. A GW-permitting UA-ICON simulation during the VortEx campaign reproduces the lidar-observed potential energy but underestimates low-frequency kinetic energy. 

A case study of the polar night jet above Kühlungsborn resolved 167 individual wave packets, showing that the jet filters GWs and that shear at its edge can excite new waves. These results provide observational benchmarks for GW parameterizations in weather and climate models.