13 Oct 2022
13 Oct 2022
Status: this preprint is currently under review for the journal ACP.

Case study on the influence of synoptic-scale processes on the paired H2O-O3 distribution in the UTLS across a North Atlantic jet stream

Andreas Schäfler1, Michael Sprenger2, Heini Wernli2, Andreas Fix1, and Martin Wirth1 Andreas Schäfler et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 2Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland

Abstract. During a research flight of the Wave-driven ISentropic Exchange (WISE) campaign, which was conducted over the eastern North Atlantic on 1 October 2017, the composition of the Upper Troposphere and Lower Stratosphere (UTLS) across the North Atlantic jet stream was observed by airborne, range-resolved Differential Absorption Lidar (DIAL) profiles. We investigate how the high variability in the paired H2O and O3 distribution along the two-dimensional lidar cross section is affected by synoptic-scale weather systems, as revealed by the Lagrangian history of the observed air masses. To this aim, the lidar observations are combined with 10-day backward trajectories along which meteorological parameters and derived turbulence diagnostics are traced. The transport and mixing characteristics are then projected to the vertical cross sections of the lidar measurements and to the H2O–O3 phase space to explore linkages with the evolution of synoptic scale weather systems and their interaction. Tropical, midlatitude and arctic weather systems in the region of the jet stream and the related transport and mixing explain the complex H2O and O3 distribution to a large extent: O3-rich stratospheric air from the high Arctic interacts with midlatitude air from the North Pacific in a northward deflected jet stream associated with an anticyclone over the US and forms a filament extending into the tropopause fold beneath the jet stream. In the troposphere, lifting related to convection in the innertropical convergence zone (ITCZ) and two tropical cyclones continuously injected H2O into dry descending air from the tropical Atlantic and Pacific forming filamentary H2O structures. One tropical cyclone that transitioned into a midlatitude cyclone lifted moist boundary layer air explaining the highest tropospheric H2O values. During the two days before the observations the air with mixed tropospheric and stratospheric characteristics experienced frequent turbulence along the North Atlantic jet stream indicating a strong influence of turbulence on the formation of the Extratropical Transition Layer (ExTL). This investigation highlights the complexity of stirring and mixing processes and their close connection to interacting tropospheric weather systems from the tropics to polar regions, which strongly influenced the observed fine-scale H2O and O3 distributions. The identified non-local character of mixing should be kept in mind when interpreting mixing lines in tracer–tracer phase space diagrams.

Andreas Schäfler et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-692', Anonymous Referee #1, 10 Nov 2022
  • RC2: 'Comment on acp-2022-692', Anonymous Referee #2, 16 Nov 2022

Andreas Schäfler et al.

Andreas Schäfler et al.


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Short summary
In this study airborne lidar profile measurements of H2O and O3 across a midlatitude jet stream are combined with analyses in tracer–trace space and backward trajectories. We highlight that transport and mixing processes in the history of the observed air masses are governed by interacting tropospheric weather systems on synoptic time scales and play a key role for the high variability in the paired H2O and O3 distributions near the tropopause.