The influence of synoptic-scale processes on the paired H2O–O3 distribution in the UTLS: case study of a North Atlantic jet stream

The distribution of H₂O and O₃ in the midlatitude UTLS is of key relevance for the Earth’s weather and climate. Tropospheric and stratospheric dynamical processes, acting on different time-scales, interact with chemistry and determine the composition of the UTLS and the extratropical transition layer (ExTL) therein. In this study, we investigate how strongly the fine-scale trace gas distribution in the UTLS/ExTL is related to interacting, tropospheric weather systems on synoptic time scales, which shape transport and mixing.

We present range-resolved, collocated lidar H₂O and O₃ measurements from a research flight during the Wave-driven ISentropic Exchange (WISE) campaign, which was conducted across a jet stream located over the eastern North Atlantic on 1 October 2017. The observations are combined with 10-day backward trajectories along which meteorological parameters and turbulence diagnostics are traced. The derived transport and mixing characteristics are projected to the vertical cross sections of the lidar measurements and to the H₂O–O₃ phase space (Tracer-Tracer space) to explore linkages with the evolution of synoptic-scale weather systems and their interaction.

We find that the formation of H₂O and O₃ filaments in the troposphere and stratosphere, the high variability of tropospheric H₂O and the formation of the ExTL mixing layer can, to a large extent, be explained by transport and mixing associated with interacting tropical, midlatitude and arctic weather systems in the region of the jet stream on synoptic time scales. The mixed ExTL air exhibits a strong influence of turbulent mixing in the jet stream during the two days before the flight. The diagnosed non-local and transient character of mixing points to the complexity of the formation and interpretation of mixing lines in T–T space.

 

The presented work is accepted for publication in ACP:

Schäfler, A., Sprenger, M., Wernli, H., Fix, A., and Wirth, M.: Case study on the influence of synoptic-scale processes on the paired H₂O-O₃ distribution in the UTLS across a North Atlantic jet stream, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2022-692, accepted, 2022.