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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/acp-2020-560
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-560
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  07 Jul 2020

07 Jul 2020

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This preprint is currently under review for the journal ACP.

PSCs initiated by mountain waves in a global chemistry-climate model: A missing piece in fully modelling polar stratospheric ozone depletion

Andrew Orr1, J. Scott Hosking1, Aymeric Delon2, Lars Hoffmann3, Reinhold Spang4, Tracy Moffat-Griffin1, James Keeble5,6, Nathan Luke Abraham5,6, and Peter Braesicke7 Andrew Orr et al.
  • 1British Antarctic Survey, Cambridge, UK
  • 2Ecole normale supérieure Paris-Saclay, Paris, France
  • 3Forschungszentrum Jülich, Jülich Supercomputing Centre, Jülich, Germany
  • 4Forschungszentrum Jülich, Institut für Energie und Klimaforschung, Stratosphäre, IEK-7, Jülich, Germany
  • 5National Centre for Atmospheric Science (NCAS), University of Cambridge, Cambridge, UK
  • 6Department of Chemistry, University of Cambridge, Cambridge, UK
  • 7Karlsruher Institut für Technologie, Institut für Meteorologie und Klimaforschung, Karlsruhe, Germany

Abstract. An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves. These enable stratospheric temperatures to fall below the threshold value for PSC formation in regions of negative temperature perturbations or cooling-phases induced by the waves even if the synoptic-scale temperatures are too high. However, this formation mechanism is usually missing in global chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate in detail the episodic and localised wintertime stratospheric cooling events produced over the Antarctic Peninsula by a parameterisation of mountain-wave-induced temperature fluctuations inserted into a 30-year run of the global chemistry-climate configuration of the UM-UKCA (Unified Model – United Kingdom Chemistry and Aerosol) model. Comparison of the probability distribution of the parameterised cooling-phases with those derived from climatologies of satellite-derived AIRS brightness temperature measurements and high-resolution radiosonde temperature soundings from Rothera Research Station on the Antarctic Peninsula shows that they broadly agree with the AIRS-observations and agree well with the radiosonde-observations, particularly in both cases for the “cold tails” of the distributions. It is further shown that adding the parameterised cooling-phase to the resolved/synoptic-scale temperatures in the UM-UKCA model results in a considerable increase in the number of instances when minimum temperatures fall below the formation temperature for PSCs made from ice water during late austral autumn/early austral winter and early austral spring, and without the additional cooling-phase the ice frost point is rarely exceeded above the Antarctic Peninsula in the model. Similarly, it was found that the formation potential for PSCs made from ice water was many times larger if the additional cooling is included. For PSCs made from NAT particles it was only during October that the additional cooling is required for the NAT temperature threshold to be exceeded (despite more NAT PSCs occurring during other months). The additional cooling-phases also resulted in an increase in the surface area density of NAT particles throughout the winter and early spring, which is important for chlorine activation. The parameterisation scheme was finally shown to make substantial differences to the distribution of total column ozone during October, resulting from a shift in the position of the polar vortex.

Andrew Orr et al.

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Short summary
Polar stratospheric clouds (PSCs) are clouds found in the Antarctic winter stratosphere, and are implicated in the formation of the ozone hole. These clouds can sometimes be formed/enhanced by so-called mountain-waves, formed as air passes over hills or mountains. However, this important mechanism is missing in coarse-resolution climate models, limiting our ability to simulate ozone. This study examines an attempt to include the effects of mountain-waves and their impact on PSCs/ozone.
Polar stratospheric clouds (PSCs) are clouds found in the Antarctic winter stratosphere, and are...
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