Utilizing airborne lidar observations for the exploration of gravity waves in the middle atmosphere

Knobloch, Stefanie (2024): Utilizing airborne lidar observations for the exploration of gravity waves in the middle atmosphere. Dissertation, LMU München: Fakultät für Physik

Abstract

The Airborne Lidar for Middle Atmosphere research (ALIMA) was first deployed for the exploration of gravity waves during the Southern Hemisphere Transport, Dynamics, and Chemistry – Gravity Waves campaign in September 2019. The thesis assesses the hypothesis that airborne lidar observations are well-suited for the explorations of gravity waves in the middle atmosphere and analyzes ALIMA observations. Observations from six nighttime research flights in the vicinity of the Southern Andes, the Drake’s passage and the Antarctic Peninsula are evaluated, as well as, data from the ECMWF Reanalysis v5 and idealized simulations are used. The airborne operation of ALIMA enables the investigation of horizontal scales of gravity waves. In order to perform a spectral analysis of the observations from ALIMA, it is first necessary to determine errors and uncertainties in the observations and data processing, as well as to characterize the dynamic situation during the observations. The thesis demonstrates that ALIMA achieves an accuracy of ±1 K and a precision of 1 K to 6 K in temperature measurements, primarily depending on the altitude. Contributions from photon noise, background photons, atmospheric transmission, and temperature retrieval from photon data are tested using additional lidar simulations. The comparison of high-resolution idealized simulations with the results of the temperature retrieval shows that the fundamental assumption of a hydrostatic equilibrium of the retrieval in the presence of non-hydrostatic gravity waves is not met, leading to an underestimation of temperature perturbations of 5 % to 20 %. Tierra del Fuego is identified as main excitation region of orographic gravity waves during September 2019 due to the shift of the polar front jet further polewards as usual. The gravity wave activity is characterized around the stratospheric polar vortex which is strongly influenced by the 2019 Southern Hemisphere sudden stratospheric warming. Thus, no distinct relationship between gravity wave activity and the strong winds at the edge of the stratospheric polar vortex is apparent. Novel horizontal wavenumber spectra derived from the airborne lidar observations are presented. The horizontal wavenumber spectra indicate a dependence of the horizontal scales which follows a −5/3 power law in the middle atmosphere and which is partly influenced by the 2019 sudden stratospheric warming. The spectral energy decreased by 25 % in the mesosphere due to reduced gravity wave activity.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 28. Juni 2024
• 1. Bericht­erstatter:in: Rapp, Markus