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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/acp-2020-458
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-458
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  09 Jul 2020

09 Jul 2020

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This preprint is currently under review for the journal ACP.

Impact of Lagrangian Transport on Lower-Stratospheric Transport Time Scales in a Climate Model

Edward J. Charlesworth1, Ann-Kristin Dugstad1, Frauke Fritsch2, Patrick Jöckel2, and Felix Plöger1,3 Edward J. Charlesworth et al.
  • 1Forschungszentrum Jülich, IEK-7 Stratosphäre, Germany
  • 2Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Germany
  • 3Institut für Atmosphären- und Umweltforschung, Universität Wuppertal, Germany

Abstract. We investigate the impact of model trace gas transport schemes on the representation of transport processes in the upper troposphere and lower stratosphere. Towards this end, the Chemical Lagrangian Model of the Stratosphere (CLaMS) was coupled to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and results from the two transport schemes were compared. Advection in CLaMS was driven by the EMAC simulation winds and thereby the only differences in transport between the two sets of results were caused by differences in the transport schemes. To analyze the time scales of large-scale transport, multiple tropical-surface-emitted tracer pulses were performed to calculate age of air spectra, while smaller-scale transport was analyzed via idealized, radioactively-decaying tracers emitted in smaller regions (nine grid cells) within the stratosphere. The results show that stratospheric transport barriers are significantly stronger for Lagrangian EMAC-CLaMS transport due to reduced numerical diffusion. In particular, stronger tracer gradients emerge around the polar vortex, at the subtropical jets, and at the edge of the tropical pipe. Inside the polar vortex, the more diffusive EMAC flux-form semi-Lagrangian transport scheme results in a substantially higher amount of air with ages from 0 to 2 years (up to a factor 5 higher). In the lowermost stratosphere, air is much younger in EMAC, owing to stronger diffusive cross-tropopause transport. Conversely, EMAC-CLaMS shows a summertime lowermost stratosphere age inversion – a layer of older air residing below younger air (an eave). This pattern is caused by strong poleward transport above the subtropical jet, and is entirely blurred by diffusive cross-tropopause transport in EMAC. Potential consequences from the choice of the transport scheme on CCM and geoengineering simulations are discussed.

Edward J. Charlesworth et al.

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Edward J. Charlesworth et al.

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Latest update: 29 Sep 2020
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Short summary
Modeling the stratosphere requires models with good representations of chemical transport. To do this, nearly all models divide the atmosphere into boxes. This creates some unwanted problems. However, the only other option is to divide the atmosphere into balloons, and this method is very complicated. Here, we use a model which uses this balloon-like method to estimate the impacts of this method on chemical transport. We find significant differences in sensitive regions of the stratosphere.
Modeling the stratosphere requires models with good representations of chemical transport. To do...
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