The climate impact of hypersonic transport

At speeds roughly between five and ten thousand km/h, hypersonic aircraft offer the promise of an extremely fast means of transport. Growing concerns about climate warming, however, direct attention to sustainability. This thesis focuses on atmospheric composition and radiation changes by considering a range of individual hypersonic aircraft designs on trajectory and route network level.

State-of-the-art Earth system models are used for simulations, and results calculated with the EMAC model are subsequently compared with simulations performed elsewhere with the LMDZ-INCA model. The comparison to a third model, i.e. WACCM, with a very similar – but independent – model setup allows even further clarification. For model validation satellite measurements (ozone, water vapor) and aircraft measurements (ozone, water vapor, temperature) are taken into account.

After the introduction in the first chapter, the second chapter is a general description of the Earth system including anthropogenic perturbations, in particular perturbations from subsonic, supersonic and hypersonic aircraft emissions followed by a detailed explanation of methods and the EMAC model setup in the third chapter. A new research finding in the context of middle atmospheric chemistry is the increased methane and nitric acid oxidation following hypersonic emissions. This effect results in a (photo-)chemical net production of water vapor and eventually increases water vapor perturbations further, which is described in detail in chapter 4. In chapter 5 an analysis of atmospheric dynamics and transport of emitted trace gases in the middle atmosphere underlines the importance of the Brewer-Dobson circulation and shows the impact of polar stratospheric clouds on water vapor perturbations during polar winter. The evaluation of multiple hypersonic aircraft designed for different cruise altitudes shows that their climate impact increases with cruise altitude and can be approximately 10-20 times as much as a conventional aircraft (chapter 6). Emissions at different hypersonic cruise altitude and latitude regions show that the climate impact can vary more with latitude of emission than with altitude of emission (chapter 7). With rf_of_hypersonic_trajectories() a software was developed to estimate the climate impact of aircraft design and flight trajectory/network options in seconds based on robust results from Earth system modelling. Using the software it is shown that a cruise altitude optimization loop can reduce the overall climate impact of a state-of-the-art aircraft design (chapter 8).

There are two methodological highlights to mention in the context of the EMAC model. The first is a new MESSy submodel H2OEMIS, which was created as part of this thesis. H2OEMIS is an interface to include water vapor emissions in EMAC model simulations, which was not possible before. This submodel will generally be of interest for future evaluations of e.g. any vehicles emitting water vapor and the impact of volcanic eruptions with EMAC. The secondmethodological highlight is the application of a novel speed-up technique during simulation runs, which reduces the simulated years by twothirds. To conclude the summary, the four following points are important to take away. This thesis brought

• A new research finding on middle atmospheric chemistry: The identification of a chemical feedback that enhances the water vapor perturbation lifetime albeit an increasing chemical water vapor destruction
• A robust estimate of the climate impact of hypersonic aircraft for both specific aircraft designs and general atmospheric and radiative sensitivities showing a large altitude and latitude dependence
• An easily accessible tool for researchers and companies to estimate the climate impact of new hypersonic aircraft designs with low cost and low time
• An estimate how the development of hypersonic aircraft would contribute to a road map to a climate optimal aircraft industry compared to conventional aircraft