Project C09:
Role of the representation of gravity waves for
downward transport into the UTLS

Brief Summary

The composition of the UTLS is determined by the mixture of air masses that traveled along different pathways. Next to direct stratosphere-troposphere exchange across the tropopause, and shallow transport from the tropics within the lower stratosphere, air is transported downward from the deep stratosphere and the mesosphere. This air is chemically processed (in particular due to the intense photochemistry), and moreover may carry signatures of emissions within the middle atmosphere. These emissions range from natural sources, such as meteoric dust, to anthropogenic contributions, like materials released during the ablation of space debris. To quantify the impact of such emissions, it is crucial to better understand and simulate the downward transport into the UTLS, where both aerosol and gas-phase substances have their strongest radiative effects. This project aims to quantify the downward transport into the UTLS, focusing on the sensitivity of transport to small-scale processes. This encompasses the role of gravity waves in driving the mean overturning circulation, and thus downwelling from the upper stratosphere and mesosphere, and the impact of gravity wave breaking on turbulent mixing. To achieve this, gravity-wave-resolving simulations with UA-ICON will be compared to coarse resolution simulations using conventional and advanced gravity wave parameterizations, the latter building on the developments in Phase 1 by Project B06. The project will quantify the sensitivity of downward transport from the mesosphere and upper stratosphere to the UTLS, as measured by transport times and the distribution of selected realistic tracers. The results of the project will be an important step towards a better quantification and understanding of the role of middle atmospheric emissions for climate.

Transport times in the middle atmosphere: Left: climatological mean residence time (i.e., average transport time an air parcel at the given location remains in the stratosphere; in colors) and age-of-air (i.e., average transport time of an air parcel from its entry into the stratosphere to the given location; black contours). Data from EMAC simulations (residence times derived by Pletzer and Grewe, 2024). Right: Fractional release of CH4 at southern high latitudes as function of month of year (colored contours), together with relative difference of age-of-air derived from SF6 to ideal age-of-air (black contours, ranging from 0.01 to 1).

Project Poster

Evaluation Poster Phase I in 2025

Members

Publications

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